7.5                                   Coats Land and Dronning (Queen) Maud Land  

The Coats Land–Dronning Maud Land area extends approximately between meridians 35º W to 45º E (see Figure 7.5.1). From west to east, the stations/bases covered in this section include:

·                         Belgrano II                  (77º 52´ 29″ S, 34º 37' 37″ W, 50 m AMSL);

·                         Halley                          (75º 35´ S, 26º 27´ W, on shelf ice);

·                         Aboa                            (73° 03´ S, 13° 25´ W);

·                         Wasa                            (73° 03´ S, 13° 25´ W);

·                         Neumayer                    (70° 39´ S, 08° 15´ W, 42 m AMSL);

·                         SANAE IV                   (71º 40´ S, 02º 50´ W, 846 m AMSL);

·                         Troll                             (72° 0´ 07″ S, 02° 32´ 02″ E, 1,298 m AMSL);

·                         Tor                                           (71° 53´ 20″ S, 05° 09´ 30″ E);

·                         Maitri                           (70º 45´ 52″ S, 11º 44´ 03″ E, 117 m AMSL);

·                         Novolazarevskaya       (70° 46´ 04″ S, 11° 50´ 54″ E, 102 m AMSL);

·                         Dakshin Gangotri        (69º 59´ 23″ S , 11º 56´ 26″ E, shelf ice);

·                         Asuka                           (71º 31´ S, 24º 07´ E, 931 m, AMSL);

·                         Syowa                          (69º 00´ S, 39º 35´ E);

·                         Dome Fuji                   (77º 19´ S, 39º 42´ E, 3,810 m AMSL);

·                         Mizuho                         (70º 42´ S, 44º 20´ E, 2,230 m AMSL).

7.5.1                            Belgrano II Station  

7.5.1.1                          Orography and the local environment

The Argentine Belgrano II Station is located at 77º 52' 29" S, 34º 37' 37'' W on the Bertrab Nunatak in Coats Land. The station is built on rock and is at an elevation of 50 m ASL and is located next to the Filchner Ice Shelf. It is about 120 km from the southern coast of the Weddell Sea and about 400 km away from the British Halley Station (see Figure 7.5.1). The station is surrounded by a huge white plateau consisting of glaciers, featureless ice and many deep crevasses. The area is subject to extreme temperatures and the region is very hostile.

7.5.1.2                          Operational requirements and activities relevant to the forecasting process

Belgrano II is the most southerly Argentine Station and is the successor to the Belgrano I Station that was established in 1955. The station is re–supplied by air so forecasts are required for flights to and from the glacier airstrip.

7.5.1.3                          Data sources and services provided

There is a full surface meteorological observing programme on the station and a resident meteorologist.

7.5.1.4                          Important weather phenomena and forecasting techniques used at the location

General overview

The area is affected by the low–pressure systems that are found in the Weddell Sea, which can either have formed as lee lows to the east of the Antarctic Peninsula or moved into the area from the South Atlantic. When the long waves are amplified and there is a steering flow from the north then lows can move down to the coast of the southern Weddell Sea and over Belgrano. Occasionally lows can cross the base of the Peninsula from the Bellingshausen Sea and onto the Ronne Ice Shelf.

Surface wind and the pressure field

Climatologically the edge of Coats Land is within the easterly flow regime that is found around much of the continent. However, offshore flow is common on many occasions, as can be seen via the coastal polynya that is often present over the southern Weddell Sea. Deep lows in the Weddell Sea can enhance the easterly flow giving gale or occasionally storm force winds. Mean‑monthly wind speeds at Belgrano II are shown in Table 7.5.1.4.1 (in Appendix 2) while mean‑monthly MSLP values at this station are shown in Table 7.5.1.4.2 (in Appendix 2).

	Key to numbered stations         1  Aboa/Wasa         2  SANAE IV         3  Troll         4  Tor         5  Dakshin Gangotri         6  Asuka         7  Mizuho          Figure 7.5.1     A map showing locations in          Coats and Dronning (Queen) Maud Lands and          adjacent areas. (Adapted from a map provided courtesy of              the Australian Antarctic Division.)

Upper wind, temperature and humidity

These fields are usually taken directly from the model fields and used to predict the winds at the aircraft flight levels if required. Adjustments to the winds can be made in the light of the satellite imagery. Because of the lack of in situ data in the area (the nearest upper–air station is Halley) the upper winds from the model should be used with care.

Clouds

Satellite imagery shows that cloud cover is rather variable around Belgrano Station with periods of extensive, non–frontal cloud or cloud associated with low–pressure systems, alternating with cloud–free interludes. During the summer months there is a plentiful supply of moisture from the coastal polynya at the edge of the ice shelf so cloud is more extensive than in winter. Cloud is monitored and predicted using satellite imagery.

Visibility: blowing snow and fog

Visibility is generally good in this area but fog can occur, especially close to the coastal lead during periods of southerly flow. Fog/low cloud can be monitored using channel 3 data from AVHRR. As elsewhere in the Antarctic, precipitation is a major factor in reducing visibility, although moderate or heavy precipitation events are fairly rare in this area.

Surface contrast including white–out

The surface contrast is rather variable around Belgrano and as with other locations depends on the amount of cloud present. Contrast is predicted using satellite imagery.

Horizontal definition

Horizontal definition is again very dependent on the amount of cloud present and can be poor because of the lack of snow–free areas and the general featureless nature of the terrain.

Precipitation

At Belgrano all the precipitation falls as snow. The area receives some clear sky precipitation as well as precipitation from low–pressure systems and non–frontal cloud. Precipitation is forecast using a combination of model output and satellite imagery.

Temperature and chill factor

At Belgrano I the January mean temperatures range from about –4^oC to –10^oC, while in July they are of the order –30^oC to –40^oC (see Table 7.5.1.4.3 (in Appendix 2)).

The extreme temperatures recorded are –2ºC and –54ºC. The near surface temperatures are strongly dependent on the cloud cover, which can be predicted in the short term by the use of satellite imagery. When quasi–stationary deep lows are present in the Weddell Sea warm air can be drawn down the eastern side of the Weddell Sea affecting Belgrano. The warmest temperatures are found when such a synoptic pattern persists for several days and there is a long fetch for the warm air.

Icing

Icing can be a problem around Belgrano because of the occurrence of cloud with supercooled water droplets. Icing is forecast using satellite imagery (especially channel 3 of AVHRR) and a knowledge of air temperatures determined from a model. When relatively warm air intrudes into the area icing can be moderate or severe because of the higher water content of the cloud.

Turbulence

There is little information available. However, as in the rest of the Antarctic, turbulence can be predicted using the model upper–level winds and from noting the locations of the jet streams.

Hydraulic jumps

No specific information on forecasting has been obtained.

Sea ice

Not relevant for Belgrano itself. However, the sea ice off the Filchner Ice Shelf and the presence of a coast polynya can have an impact on the weather of the region as a whole. The sea ice is monitored via satellite imagery.

Wind waves and swell

No relevant for this area.

7.5.2                                Halley Station  

7.5.2.1                          Orography and the local environment

Halley Station is situated at 75º 35´ S , 26º 36´ W on the Brunt Ice Shelf (see Figure 7.5.1). The ice shelf is flat and the base is situated about 25 km from the seaward edge of the shelf and about 90 km from the grounding line of the shelf where the ground begins to rise rapidly to the polar plateau. Near the base the seaward edge of the shelf is too high to allow the unloading of a ship directly onto the shelf but several indentation (locally know as creeks or bays) fill with sea ice and ships can be unloaded onto this and then the cargo can be pulled up wind tails onto the ice shelf.

7.5.2.2                          Operational requirements and activities relevant to the forecasting process

Halley Station is primarily a station for the study of meteorology and the upper atmosphere. The base is normally visited twice during the summer by a ship bringing stores and personnel. The unloading of the ship at the edge of the ice shelf is dependent on the weather and the state of the sea ice. If good sea ice is present in the creeks close to the base the journey from the ship to the base is relatively short and so less dependant on good weather. Often, however, it is necessary for the ship to moor some 60 km away at the low shelf and then the trip from the ship to the base for heavily loaded cargo sledges can take up to 12 h and is heavily weather dependent.

The station also acts as a base for British Antarctic Survey field activities in Dronning Maud Land and the eastern half of the Ronne Ice Shelf and towards the pole. The level of activity can vary a lot from year to year but always includes some flying to support the servicing of several Automatic Geophysical Observatories. It is normal for up to two twin otter aircraft to be stationed at Halley for a period during the summer season.

7.5.2.3                          Data sources and services provided

Forecasts for Halley are normally issued by the forecaster at Rothera who has responsibility for all forecasts issued for British Antarctic Survey activities. These forecasts are only available during the summer months and are normally issued in the morning, although this varies from year to year with operational requirements. An HRPT receiver is located at Halley and high resolution AVHRR imagery is available.

UK Meteorological Office forecast model fields and surface observations from the GTS are sent to Halley via an Inmarsat link. The UK Meteorological Office model is quite good at representing synoptic scale systems over the ocean and coastal regions but has more difficulty with mesoscale systems that can develop near to Halley (see below). Inland, over the high Antarctic plateau, the model has more difficulty and output must be used with more care. In all cases satellite imagery should be used to identify systems missed by the model. The surface wind on the Brunt Ice Shelf is dominated by drainage flow down the slope from the high plateau and so the surface gradient shown in the model fields is often in error.

7.5.2.4                          Important weather phenomena and forecasting techniques used at the location

General overview

Because of Halley Station’s position on the edge of the Weddell Sea the climate is largely dependent on the amount of sea ice in the Weddell Sea. During the summer, when there is little sea ice in the eastern Weddell Sea, temperatures tend to hover around freezing, but during the winter when there is little open water present temperatures can drop to –50ºC during clear calm conditions. At these times a strong surface inversion forms and the temperature just a few hundred metres above the surface can be 20–30 ºC higher. When the wind strengthens the stable boundary layer tends to break down and the temperature can rise 20–30ºC in an hour or two.

In general the weather at Halley is controlled by large synoptic scale systems that form in the circumpolar trough and track south into the Weddell Sea or lee lows that form on the east side of the Peninsula and then move slowly across the Weddell Sea.

Surface wind and the pressure field

Mean–monthly wind speeds at Halley are shown in Table 7.5.2.4.1 (in Appendix 2) while mean–monthly MSLP values at this station are shown in Table 7.5.2.4.2 (in Appendix 2).

The local orography of the plateau near to the ice shelf has a large controlling effect on the surface wind, which is predominately easterly with the strongest winds always coming from that direction. Northeasterly and southwesterly are the next favoured directions but the wind is usually weaker from these directions.

Large–scale synoptic depressions are capable of producing strong easterly winds at Halley with mean speeds of around 15 m s^–1 (~30 kt) or more. Several occasions have been reported of occlusions moving around a low in the Weddell Sea became slow–moving as they approached Halley. This gives stronger easterly winds than the gradient suggested, probably because of squeezing against the plateau to the south. This can give prolonged periods of gales and blowing and falling snow.

Strong easterly winds at Halley are often preceded by a light westerly flow, induced by the surface pressure field. This flow will advect mild air over the area, consequently the temperature difference between the Halley area and the upsloping ice sheet to the south will increase significantly. After a few days the temperature gradient becomes very tight resulting in the initiation of a katabatic wind from the east.

The eastern coast of the Weddell sea is favoured for the formation of mesocyclones, particularly when strong thermal gradients build up along the coast due to mild air being advected into the area from further north. Mesocyclones developing off the coast have been known to produce severe weather (eg Christmas 1995) at Halley and are very difficult to forecast. Fortunately, although mesocyclones are a relatively common occurrence, the severe weather is quite rare.

During periods with relatively light winds and clear skies a strong surface inversion can develop on the Brunt ice shelf. This means that the boundary layer is extremely stable and internal gravity waves can form – although these do not tend to cause operational problems for aircraft.

Upper winds, temperature and humidity

These upper–level fields are well represented by the UK Meteorological Office model and present no special forecasting problem, although adjustments may have to be made occasionally after comparison with satellite imagery. (Mean January and July upper–level wind roses for Halley Station are included in Figures A3–9 (a) and A3–9 (b) (in Appendix 3) while mean–temperature profiles for this station are also shown in Appendix 3 as Figures A3–3 (a) and (b) .

Clouds

Clouds are generally layer in form and it is not uncommon to have stratus with a base as low as 150–300 m (~500–1,000 ft). When the cloud is uniform surface contrast tends to be poor and this can made operations very difficult. When open water is present close to the coast "water sky" (the dark sea reflected in the clouds) is often seen.

Visibility: blowing snow and fog

Fog can sometimes develop over the leads in the sea ice and is occasionally advected into Halley on a light westerly or northerly wind and most fog occurs when the wind is from this direction.

The main cause of a reduction in visibility and surface contrast at Halley is blowing snow. It is normal to stop all but essential outdoor activity during heavy blowing snow.

Surface contrast

No specific information on forecasting has been obtained.

Horizontal definition

No specific information on forecasting has been obtained.

Precipitation

During the summer the precipitation is almost always in the form of snow, rain being very rare. As convective clouds are relatively rare this far south most precipitation comes from layer clouds and these can be as thin as 300 m (~1,000 ft). During the winter some of the precipitation falls as “precipitation from a clear sky” (diamond dust) although this does not add appreciable to the total yearly accumulation.

Temperature and chill factor

No specific information on forecasting has been obtained. Mean–monthly temperatures for Halley Station are shown Table 7.5.2.4.3 (in Appendix 2).

Icing

No specific information on forecasting has been obtained.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

It is thought that hydraulic jumps can form in the stable boundary layer in the zone where the katabatic airflow down the grounded continental ice meets the flat ice shelf. This can show up in infra–red satellite imagery as a dark (warm) band along the junction between the continental and shelf ice.

Sea ice

No specific information on forecasting has been obtained.

Wind waves and swell

The ice in the Weddell Sea damps out most swell long before it reaches the Brunt Ice Shelf. It is rare for there to be an area of open water large enough for wind waves to get to any significant height. However, knowledge of the wind and fetch can be used to estimate the significant wave height in any area of open water that does form if this is needed.

7.5.3                                Aboa and Wasa Bases  

7.5.3.1                          Orography and the local environment

The Swedish research station Wasa was built on Vestfjella, Dronning Maud Land (see Figure 7.5.1) during the 1988/89 Antarctica expedition. It is situated at 73 ^o 03´ S, 13 ^o 25´ W on the Basen nunatak. Nearby is the Finnish Station Aboa (established in 1988) that, together with Wasa, makes up the so–called Nordenskiöld base. The site is 120 km inland from the marine edge of the Riiser–Larsen Ice Shelf and is at an elevation of 467 m (~1,531 ft) AMSL. Wasa is operated by the Swedish Polar Research Secretariat.

7.5.3.2                          Operational requirements and activities relevant to the forecasting process

Wasa is a summer–only station, which has a helicopter landing area and forecasts are required for helicopter operations. Aboa is occupied from December to February.

7.5.3.3                          Data sources and services provided

There is no meteorological service at the station for air traffic. A Milos–type AWS is located at the station.

7.5.3.4                          Important weather phenomena and forecasting techniques used at the location

General overview

This site is just inland of the coast at an elevation of 400 m so is affected by weather systems in the Antarctic coastal region.

Surface wind and the pressure field

No specific information on forecasting has been obtained.

Upper wind, temperature and humidity.

No specific information on forecasting has been obtained.

Clouds

No specific information on forecasting has been obtained.

Visibility: blowing snow and fog

No specific information on forecasting has been obtained.

Surface contrast including white–out

No specific information on forecasting has been obtained.

Horizontal definition

No specific information on forecasting has been obtained.

Precipitation

No specific information on forecasting has been obtained.

Temperature and chill factor

No specific information on forecasting has been obtained.

Icing

Icing is potentially a problem in this area since there will be a plentiful supply of supercooled water droplets.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

There are no reports of hydraulic jumps in this area.

Sea ice

Not relevant at this location.

Wind and swell

Not relevant at this location.

7.5.4                                Atka Bay–Neumayer Station–Cape Norwegia  

7.5.4.1                          Orography and local environment

Neumayer (70° 39´ S, 008° 15´ W) is situated on the Ekström Ice Shelf at about 5 km distance from the southeastern part of Atka Bay, 42 m above sea level (see Figure 7.5.1). The Ekström Ice Shelf has a homogenous flat surface sloping gently upwards to the south. Except for some nunataks about 100 km south of Neumayer no ice–free land or mountains exist. The orographic conditions around the area of Cape Norwegia are nearly the same.

7.5.4.2                          Operational requirements and activities relevant to the forecasting process

The most intensive research activities here take place in the summer season. During this time two Dornier 224 aircraft are frequently based at Neumayer. They are used to deploy field parties; for traverses; and for logistic operations. More than 30 scientists live on the station in addition to the station crew at Neumayer and the neighbouring region during summer. The Alfred Wegener Institute for Polar Research in Bremerhaven operates one research vessel ("Polarstern", DBLK) that operates in the southern summer near Neumayer, Cape Norwegia, in the Weddell Sea and near the Peninsula. Two helicopters are stationed on board Polarstern.

7.5.4.3                          Data sources and services provided

At Neumayer Station there is a permanent satellite communication link to receive observations from the GTS and forecast charts up to 48 h from the ECMWF model once a day. Synoptic observations are made every three hours and transferred directly into the GTS by e–mail and into the Internet address at:

http://www.awi.de/MET/Neumayer/latest_obse.html.

Once a day (at about 0100 UTC) a radiosonde is launched to measure the vertical profiles of air pressure, temperature, humidity and wind vector. The resulting TEMP–CODE is available without delay at http://www.awi.de/MET/Neumayer/nrt–temp and via the GTS. By using a satellite image receiver (Sea Space) up to six passes of NOAA and DMSP satellite data are processed daily (AVHRR, SSMI), (see http://www.awi.de/MET/Neumayer/satpics/). The station meteorologist at Neumayer provides actual synoptic surface observations (METAR) and descriptions of the lower atmosphere's structure and satellite images on demand.

Polarstern's meteorological office is staffed with one meteorologist (forecaster) and one Information Technology (IT) assistant. Synoptic observations are made every three hours and transferred directly onto the GTS by a DCP. Once a day the ship–meteorological office receives via E–mail, or satellite communication, analyses and forecast charts of surface pressure, 500–hPa, and sea state, up to 144 h ahead based of the ECMWF and the DWD models. Observations from the GTS are also available via E–mail/Inmarsat. The database is complemented with synoptic data received by short–wave exchange, because of poor satellite communications at higher latitudes. One radiosonde is launched every day at noon while for flight operations other radiosondes are launched if required. The meteorologist on board is responsible for provision of all forecasts for Polarstern, Neumayer Station, and for all ship, flight, and ground operations and for field parties in the vicinity.

7.5.4.4                          Important weather phenomena and forecasting techniques used in the location  

General overview

During the summer season the weather is dominated by low–pressure systems moving across the northern Weddell Sea from the Antarctic Peninsula in an easterly direction with periods of two to seven days. Ahead of the low–pressure systems relative warm air with high humidity streams in from a northeasterly direction mostly accompanied by moderate to strong snowfall. Sometimes fog develops due to the high dew–points in relation to the cold water.

Moderate to strong southerly winds with cold, dry air and good visibility are found to the rear of the low–pressure systems with cloudy to fair sky. It can often be observed that eastward moving lows lose their speed if they move to a position under an upper low–pressure system. One of the most frequent positions where lows become stationary is situated east of Neumayer, near Novolazarevskaya: this gives mostly clear weather with katabatic flows over the Neumayer region.

The meteorologist on Polarstern produces surface pressure analyses at 0000 and 1200 UTC, and occasionally at 0600 UTC. The analyses cover the operational area of Polarstern usually including the Antarctic Peninsula, the Weddell Sea and Neumayer regions. The analysis of frontal systems is supported by satellite imagery in combination with surface observations.

Synoptic scale weather systems are quite well forecast by using the DWD and ECMWF models. Difficulties often occur when a low–pressure system is moving up against the barrier of the Antarctic Peninsula. Low–pressure developments leeward are sometimes not predicted by the model but they can be analysed well by satellite imagery. Model forecasts often produce speeds of movement of these lows that are too fast, with phase differences of more than 24 hours.

The development of polar lows is hardly ever observed during anticyclonic conditions, at the ice edge north and northwest of Neumayer region. Analysis and forecast of these systems is only possible using HRPT satellite imagery and in situ data. Especially in the summer season, the forecasting of polar lows near Neumayer is very important for flight operations, field parties or other logistic work. In polar lows, visibilities can change rapidly to poor conditions due to drifting snow and precipitation accompanied by a low cloud base.

Surface wind speed and pressure field

Mean–monthly wind speeds at Neumayer are shown in Table 7.5.4.4.1 (in Appendix 2) while mean–monthly MSLP values at this station are shown in Table 7.5.4.4.2 (in Appendix 2).

The most frequent wind directions observed are northeast to east caused by eastward moving low–pressure systems north of the Neumayer region but also by the local orography. There are two secondary maxima observed around the directions south and west–southwest, as may be seen in Figure 7.5.4.4.1 (in Appendix 2). The maximum around west–southwest is caused by high–pressure ridges swinging east from the northern Weddell Sea, while the southerly maximum is forced by katabatic flows.

Synoptic disturbances are responsible for the maximum around 90° and a wind speed about 13 m s^–1 (~25 kt). The katabatic flows tend to give a direction of around 180° and a speed of 5 m s^–1 (~10 kt). Wind speeds above 20 m s^–1 (~40 kt) are restricted to easterlies. Moderate winds between 8 and 18 m s^–1 (~16 and 35 kt) may also occur from west to southwest. Southerly winds always stay below 10 m s^–1 (~20 kt).

Wind direction and wind speed can be forecast using the hand drawn analysis of surface pressure and the model data (wind vectors or surface pressure gradients) with corrections due to local orography. In anticyclonic situations with light synoptic pressure gradients katabatic flows tend to dominate.

For the area around Cape Norwegia the easterly geostrophic wind is enhanced by katabatic winds. The increase in wind speed reaches 5 to 10 m s^–1 (~10 to 20 kt). Thus wind speeds up to 28 m s^–1 (~55 kt) are measured near the Cape. The katabatic winds can be calculated and forecast in combination with the ground temperature (sea surface temperature), the temperature on the mountain plateau and slope of the ice sheet. This katabatic effect is shown in Figure 7.5.4.4.2 and Figure 7.5.4.4.3. Figure 7.5.4.4.2 shows the frequency distribution of the measured wind forces between 24 January and 2 February 1998 on Polarstern near Cape Norwegia. The frequency distribution of wind direction for wind speeds greater or equal 14 m s^–1 (~28 kt) is shown in Figure 7.5.4.4.3. It is evident that the highest values correspond to easterly and northeasterly directions. While cruising near Cape Norwegia it is important to know that a high wind speed is generated due to the katabatic effect.

Upper wind, temperature and humidity

These fields are predicted using the model forecasts in combination with the daily radiosonde data from Neumayer and Polarstern. Usually the circumpolar vortex, with increasing westerly winds with height, prevails while an easterly wind is observed mostly in the lowest two kilometres of the troposphere. Only between November and February do easterly winds exist in levels above two kilometres.

Clouds

The cloud cover and type are mainly related to frontal systems. The heights of cloud bases are determined by a laser ceilometer. Cloud bases and tops are also calculated by analysing the latest radiosonde ascent. Cloud forecasts can be made by studying the high–resolution satellite imagery in combination with measured cloud tops and bases with consideration of the general synoptic situation.

A special effect is often observed near Neumayer Station in relation to cloud cover. On the southern flank of low–pressure systems the sky becomes suddenly filled with scattered cloud, or the sky clears in correlation with wind direction veering from 90° to 110°. This happens while mild north–northeasterly origin air masses are replaced by cold and dry air masses due to katabatic flows.

Another typical situation is often observed when frontal systems approach Neumayer Station. The start of precipitation with a descending cloud base occurs just before frontal systems reach Neumayer Station with winds backing from east to north–northeast. This is an effect caused by strong ageostrophic components in front of the low–pressure system due to the orography.

Visibility: blowing snow and fog

Visibility is an important parameter in the Antarctic region normally estimated by visual observations with sight marks but also measured on Polarstern by using a Videograph III. Fog sometimes develops near the Neumayer region on the forward side of low–pressure systems due to the high dew–point of the air over the cold water or the shelf ice. Also sea smoke exists when cold air due to katabatic flow moves over warm open water. For prediction of visibility, including fog, satellite imagery, in situ observations and radiosonde data processed with special software are used.

At Neumayer Station poor visibility conditions are mainly associated with drifting or blowing snow starting at wind speeds of more than 7 m s^–1 (15 kt). About 40% of all visual observations report these kinds of significant weather, mostly in combination with white–out. Blowing snow at Neumayer makes any air operations impossible. Even land operations are then restricted to the closest neighbourhood. Thus visibilities have to be forecast carefully.

Surface contrast including white–out

Even in summer poor surface contrast or white–out is observed in the vicinity of Neumayer. These situations are mostly accompanied by precipitation and an opaque cloud layer on the forward side of low–pressure systems. But also under high pressure poor surface contrast is possible in overcast conditions of low stratus or stratocumulus layers. On the ice shelf the surface contrast is additionally influenced by blowing snow.

A forecast of surface contrast can be done by using satellite imagery bearing in mind the general synoptic situation as well as using a regression formula (Equation 7.5.4.4.1) developed during several expeditions with Polarstern.

CON = 0.00002*VIS + 0.0634*RH + 0.0014*SUN –0.135*ICE – 0.9462*COV + 4.092656                                                                                                                      Equation 7.5.4.4.1

where VIS is the horizontal visibility in km; RH is the relative humidity in percent; SUN is the relative azimuth angle in degrees between observer and sun position; ICE and COV are cover of ice and cloud in oktas.

Surface contrast is poor for CON <= 2 and very good for CON 9 to 10. Poor surface conditions over the sea, known as "glassy sea“, are sometimes observed on Polarstern in light air with sea state like a "mirror“.

Horizontal definition

No specific information on forecasting has been obtained.

Precipitation

Precipitation is possible during all seasons of the year. Most of the precipitation is slight to moderate with snow brought by frontal systems. Either drifting or blowing snow makes the quantification very difficult. During summer drizzle and rainfall occur rarely. Even with high pressure, snow, rainfall and showers are possible in combination with low stratus.

Temperature and chill factor

Surface inversions can be detected by analysing radiosonde data. The inversions are normally created by radiative cooling in light air or by descending air masses in anticyclonic situations. The thickness of the inversions extends during wintertime approximately two kilometres while in summer it is typically less than one kilometre. Inversions caused by radiative cooling become unstable near noon. In anticyclonic situations inversions become well established and assist in maintaining cloud cover.

Forecasting of temperature during the summer season is mostly tied to the synoptic situation. In summer the temperature can be above freezing with values up to 5°C ahead of low–pressure systems or in sky clear conditions without wind. Following the passage of lows, in combination with katabatic winds, temperatures down to –25°C are observed. With wind speeds from 5 to 7 m s^–1 (~10 to 15 kt) wind chill temperatures below –50°C can be calculated using the formula of Schwerdtfeger (1984). Mean–monthly temperatures for Neumayer Station are shown in Table 7.5.4.4.3 (in Appendix 2) while the distribution of mean temperature as well as maximum– and minimum–temperature for every month is shown in Figure 7.5.4.4.4(in Appendix 2).

Icing

Icing is normally tied to frontal systems. Light, moderate and severe icing is observed in the vicinity of Neumayer. Supercooled droplets are observed only occasionally at Neumayer Station. Analysis and forecasting of this parameter is prepared by using the radiosonde data processed by special software and by use of the so called "–8D–curve" (see Section 6.6.9.1).

Turbulence

Turbulence is correlated to the general synoptic situation and the local orography. Forecasts of turbulence are provided using radiosonde data and by calculating the vertical wind profile.

Hydraulic jumps

Hydraulic jumps have not yet been investigated near Neumayer region.

Sea ice

Atka Bay is mostly covered with close fast ice (first–year and some parts multi–year–ice) with some icebergs of medium size. Only from January to March does Atka Bay experience open ice conditions, or is free of ice. Pack ice is located about 15 km north of Neumayer. Sometimes, strong southwesterly to westerly winds open a coastal polynya. The sea ice state can be well analysed with AVHRR satellite images. For example, in Figure 7.5.4.4.5 the coastal region around Neumayer can be seen. Forecasts in relation to sea ice cover in Atka Bay are done using model surface winds in combination with satellite imagery.

Wind waves and swell

In summer wave heights between one to four metres are observed in the outer Atka Bay and at the northern edge of the pack ice due to eastward moving lows north of Neumayer region. But mostly in the inner Atka Bay the sea is subdued by fast ice. Waves and swell forecasts are needed for logistic work if Polarstern is alongside the ice shelf edge. Predictions of sea state are done using model surface wind with the WMO standard wave prediction algorithm.  Model sea state forecasts can be used if no fast ice exists windward. The quality of wave forecasts from models in Antarctic waters such as in the Weddell Sea, around the Antarctic Peninsula, and in regions with sparse meteorological data, are relatively poor. Forecasts for four to six hours ahead can be produced using the techniques presented in the WMO (1988) handbook of wave analysis and forecasting.

7.5.5                                SANAE Station 

The South African National Antarctic Expedition (SANAE) Station is situated near the northeast extremity of a Peninsula that separates Jelbut Ice Shelf from Finibul Ice Shelf about 32 km to the east (see Figure 7.5.1). The station, which is now maintained by the South African Government, was formerly located at 70º 30´ S, 2º 38´ W, and was originally established in 1957 by the Norwegian government.

7.5.5.1                          Orography and Local Environment

In this section we discuss the weather regimes for two stations, the old SANAE III, and the new SANAE IV base at Vesleskarvet. SANAE III (70º 18' S, 2º 21' W, 62 m AMSL) is located on the Fimbulisen ice shelf and has been abandoned since1996. Its emergency base (known as E–Base) is now used as a logistics centre and forwarding point for cargo (to SANAE IV) during the austral summer.

SANAE IV is situated on the southern buttress of a nunatak (71º 42' S, 2º 48' W, 815 m AMSL) and has been occupied permanently since the summer of 1997/1998. Apart from some exposed rock, the southern buttress is covered by a smooth snow surface sloping towards the east. The buttress terminates in a 200 m (~260 ft) high cliff (running approximately north to south) some 50 m west of the station.

All climate data provided in this section were obtained from the South African Weather Bureau climate archives. Owing to its distance from the barrier edge and altitude, certain meteorological parameters observed at SANAE IV may differ significantly from those at SANAE III and these differences are discussed where relevant.

7.5.5.2                          Operational Requirements

A relief vessel brings fresh supplies to the base once a year (from December to February). In years when the lack of sea ice precludes building a ramp down to the bay ice, helicopters are used extensively to cargo sling supplies to the ice shelf. The helicopters also make regular flights between the ship and SANAE IV to transfer personnel and/or equipment. The annual supply of polar diesel is pumped directly from the ship into fuel bladders located on sleds. All the aforementioned tasks are highly dependent on the weather and sea conditions in the vicinity of the ice shelf.

7.5.5.3                          Data Sources and Services Provided

All upper–air measurements at SANAE stopped with the shifting of the base. The upper–air programme on the vessel SA Agulhas followed suit a few years later. From the beginning of 2000 manual surface weather observations were restarted at SANAE IV from the same location as the AWS (which reports via Argos).

Dedicated forecasts (valid up to four days ahead) are provided to assist with the logistics and are issued during hand–over and voyages to and from the ice shelf. When compiling a good forecast, an accurate surface analysis is crucial and surface charts for the Southern Atlantic are analysed at 6–hour intervals. The surface pressure field is analysed using observations from land, ships and drifting weather buoys, as well as the UKMO "first guess" pressure field and METEOSAT images. The METEOSAT imagery is particularly useful when determining the position of depressions and their corresponding frontal systems.  These images have proven to be a very useful analysis and nowcasting tool, but south of 60º S, distortion makes interpretation of the images difficult.

Surface winds are forecast using the gradient winds inferred from the European Centre for Medium Range Weather Forecasting prognostic surface pressure fields. Other forecast parameters include the expected weather and visibility. In situ surface and upper–air data (when available) are available on the GTS and are taken into consideration when issuing short–term forecasts. A very recent development in the SAWB has been the ability to display a vast array of parameters at 6–hour intervals (in plan view or the vertical) using PCGRIDDS (a PC based Gridded Information Display and Diagnostic System). World Area Forecast System data (1.25º by 1.25º horizontal resolution) is now available for the forecast area and in the future (depending on the model's accuracy), and these could assist in improving forecasts of cloud cover, precipitation probability and winds for various flight levels.

Sea conditions (swell period and height, as well as total sea) are forecast up to four days ahead using the UKMO swell model data available every 12 hours. No swell data are currently available south of 57.5º S and no forecasts for swell or wind waves are issued south of this latitude.

7.5.5.4                          Important Weather Phenomena and Forecasting Techniques

General overview

Deep synoptic–scale depressions embedded within the circumpolar trough can cause blizzards lasting up to four days and severely hamper relief operations. Generally, unsettled weather and strong winds (typically easterly) can be expected prior to and during the passage of a depression north of the station, with clearing skies and moderating winds (typically south–easterly) observed in its lee. Mesoscale low–pressure systems are not handled well by the global model, but can also have a significant impact the weather. Satellite imagery is currently the only means the SAWB has of detecting mesoscale lows and monitoring their movement.

An AWS has been operational at SANAE IV since 1997, but no climate analysis of the data has yet been undertaken. However, a subjective analysis of temperature and wind data from June 1997 through August 1999 has been made by the authors and the results are discussed where relevant. Two authors (J. Brimelow and de Broy Brooks) conducted a detailed evaluation of the ECMWF prognostic surface pressure fields and gradient winds (compared with observations made at SANAE III and IV) during February and March 1998. Some of these results, together with observations made during other relief seasons are also presented in the following sections.

Surface Winds and the pressure field

When issuing forecasts for the ice shelf, accurately forecasting the wind speed and direction is perhaps most important. This is due to their impact on the movement and break–up of the sea ice, visibility, helicopter flights, crane operation and wind–chill. During storms, sustained wind speeds as high as 28 m s^–1 (~55 kt) (with gusts exceeding 50 m s^–1 (~100 kt) are possible.

The wind speed statistics for SANAE III are summarized in Table 7.5.5.4.1 (in Appendix 2). Similarly the direction statistics are shown in Table 7.5.5.4.2(in Appendix 2). The air–flow displays a strong easterly component, with 47.7% of the winds blowing from the southeast quadrant. The most frequent and strongest winds are typically easterly, with a mean annual frequency of 16.6% and mean speed of about 24 knots. Winds from the northwest and northeast quadrant have the lowest frequency at 5.3% and 11.2% respectively. Winds from the northwest quadrant are generally the weakest, with a mean speed of approximately 6 m s^–1 (11 kt).

May is typically the windiest month, with a mean speed of 9.8 m s^–1 (~19.1 kt). The lowest mean wind speed (5.5 m s^–1 (~10.7 kt)) is observed in January. Calms occur most frequently in January and are observed an average of 14.5% days per month.

During storms, the wind speeds observed at SANAE IV are noticeably stronger than those at the coast. For the period 1997 to 1999, sustained winds greater than 33 m s^–1 (64 kt) (hurricane force) have been observed every month of the year at SANAE IV during storms associated with depressions.

Forecasting the onset and duration of strong winds is critical for relief operations and safety. The following guidelines have been determined when considering issuing a gale warning for the ice shelf:

·                         Gale–force east–northeast/east–southeast winds can be expected when a deep depression (central pressure typically lower than 980 hPa) is located between 15º W and 05º E and tracks south of 65º S.

·                         Issuing wind forecasts for the ice shelf is difficult at the best of times and this is compounded by the inferior performance of the numerical models south of 60º S. Experience and case studies have shown that with the passage of a deep low south of 65º S, the ECMWF model underestimates the wind speed at the ice shelf by 20–50% and under extreme conditions by as much as 100%. The reason for the model underestimating the speed is believed to be threefold: firstly, the model tends to place the centre of the depressions too far north; secondly, the model underestimates the intensity of the continental high and rather than concentrating the pressure gradient along the ice/sea interface, spreads the gradient across the coastal zone; and thirdly, it is possible that the katabatic wind (which has an easterly component) can be superimposed on the synoptic flow, thereby further increasing the wind speed.

·                         However, although the model does not display much skill in accurately forecasting the wind speeds during storms, it is useful for determining trends and provides valuable guidance regarding the onset and cessation of strong winds.

·                         Katabatic Winds (i): SANAE IV frequently experiences strong to gale–force south–easterly katabatic winds following the passage of depressions. Katabatic winds reaching the coast are generally weaker and of shorter duration. The following criteria have been used with a fair degree of success when determining the likelihood of a strong (> 15 m s^–1 (> ~30 kt) katabatic wind event at SANAE IV and/or the coast within 24 h following the passage of a depression: (a) passage of a slow–moving deep depression south of 65º S, followed by the formation of a ridge of high pressure west of Greenwich; (b) rapid clearance in the lee of the depression; and (c) formation of a relatively deep surface inversion (at least 1,000 ft deep).

·                         Katabatic winds (ii): Another forecast sequence that has some success involves cyclogenesis just east of Greenwich with the Polar High extending a ridge northwards of 70º S and west of Greenwich. During weakly forced synoptic conditions, i.e. weak synoptic–scale pressure gradients, a low–level temperature inversion develops over the ice shelf. Under such conditions, highly directionally consistent inversion winds are observed at SANAE IV. Preliminary analysis of the data indicates that these winds are typically 120º at 8 m s^–1 (~15 kt) during the summer months.

Upper wind, temperature and humidity

No specific information on forecasting has been obtained.

Clouds

Cloud cover is greatest in mid–summer (December to January) with a mean of 5.8 oktas. This can be attributed to the lack of pack ice and resultant increase in moisture content of the air. Cloud cover is a minimum in mid–winter (July to August), with a mean of 4.2 oktas. No climate data of cloud type or base height are currently available. During the relief period cloud base heights are estimated from the latest upper–air sounding made from the ship.

Experience has shown that the cloud cover is less at SANAE IV and the weather is likely to clear more rapidly after a storm than at the coast. This is most likely due to its distance from the coast and in turn open water.

Visibility

The most common factors responsible for reducing visibility on the ice shelf are falling snow, blowing snow and to a lesser extent fog.

Fog is rare and limited to the summer months. Conditions conducive to the formation of fog are a prolonged period (several days) of light winds having a northerly component, and the absence of sea ice. No statistics are available for the mean–monthly occurrence of fog at SANAE III. Fog is not expected to be a problem at SANAE IV, due to its altitude and distance from the coast.

Strong katabatic winds, although generally associated with clear skies, can significantly reduce the visibility due to blowing snow.

Surface contrast

Blowing snow can significantly reduce the contrast and horizontal visibility near the surface. The extent of blowing snow depends on many factors, for example the composition or texture of snow and even the amount of loose snow. As a rule of thumb, winds of around 10 m s^–1 (~20 kt) cause drifting snow and those around 15 m s^–1 (~30 kt) create blowing snow; this usually reduces the visibility sufficiently to suspend helicopter flights. Increasing cloud cover also decreases the amount of contrast, especially when the cloud cover is in the form of a uniform deck or layer.

Horizontal definition

Cloud can be responsible for obliterating the horizon, even for aircraft flying several thousand feet above the surface.

Precipitation

At SANAE III, precipitation is almost exclusively in the form of snow, with liquid precipitation very rarely observed during the summer months. The most significant precipitation events are associated with the passage of deep depressions near the station. Mesolows can also be responsible for heavy falls of snow, but their dynamics and characteristics have not yet been studied in detail at this location.

Temperature

The temperature statistics for SANAE III are displayed in Table 7.5.5.4.3(in Appendix 2). Temperatures display a marked seasonal variation, with temperatures ranging from as high as +7ºC in the summer to as low as –50ºC in the winter. The mean annual temperature is –16.9ºC. The warmest month is January (mean temperature of –3.6ºC), with July and August the coldest months (mean temperature of about –28ºC). Temperature forecasts are currently not issued during relief operations.

During the summer months, temperatures at SANAE IV tend to be a couple of degrees cooler than SANAE III, with a mean temperature of approximately –7ºC and –10ºC in January and February respectively. Temperatures have been observed to briefly go above freezing in mid–summer. A rather puzzling observation from the preliminary data analysis is that since 1997, the lowest temperature recorded at SANAE IV is only –37ºC.

Icing

No specific information on forecasting has been obtained.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

No specific information on forecasting has been obtained.

Sea ice

No specific information on forecasting has been obtained.

Wind waves and swell

No specific information on forecasting has been obtained.

7.5.6                                Troll and Tor Stations  

7.5.6.1                          Orography and the local environment

Troll (72° 00' 07'' S, 02° 32' 02'' E) and Tor (71° 53' 20'' S, 05° 09' 30'' E) are two Norwegian summer–only stations located in Dronning Maud Land at elevations of 1298 and 1625 m above mean sea level respectively. Troll is built on a solid rock surface and is 250 km from the coast. Tor is located in an area called Svarthamaren while Troll is in Jutulsessen.

7.5.6.2                          Operational requirements and activities relevant to the forecasting process

Troll was opened in February 1990 and surface meteorological observations are made at the site. Tor was established in January 1993, but no information is available about the meteorological activities.

7.5.6.3                          Data sources and services provided

Surface meteorological observations are made at Troll. No weather forecasting is carried out at either station.

7.5.6.4                          Important weather phenomena and forecasting techniques used at the location

General overview

These stations are in the transition zone between the more maritime climate in the coastal sector and the cold, continental regime of the high plateau. Major weather systems can affect the area, especially when the long waves are amplified, but the diamond dust precipitation characteristic of the interior is also experienced.

Surface wind and the pressure field

No specific information on forecasting has been obtained.

Upper wind, temperature and humidity

No radiosonde data are available for the region but upper–air conditions can be predicted using numerical weather prediction model output.

Clouds

No specific information on forecasting has been obtained.

Visibility: blowing snow and fog

No specific information on forecasting has been obtained.

Surface contrast including white–out

No specific information on forecasting has been obtained.

Horizontal definition

No specific information on forecasting has been obtained.

Precipitation

No specific information on forecasting has been obtained.

Temperature and chill factor

No specific information on forecasting has been obtained.

Icing

No specific information on forecasting has been obtained.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

No specific information on forecasting has been obtained.

Sea ice

Not relevant at this location.

Wind waves and swell

Not relevant at this location.

7.5.7                                Maitri and Dakshin Gangotri Stations  

The Indian Scientific Expedition to Antarctica has operated since 1981. For the first two years of operation, Indian scientists took surface meteorological observations during the summer period only, housed in temporary shelters on the Prince Astrid coast a few kilometres away from the open sea. During the third expedition in 1983 India established the "permanent" scientific Dakshin Gangotri (69º 59´ 23″ S, 11º 56´ 26″ E) on an ice shelf. However, as this station began sinking in the ice, a second permanent station, Maitri (70º 45´ 52″ S, 11º 44´ 03″ E, 117 m) was set up in the Schirmacher Range (see Figure 7.5.1) during the eighth Indian Expedition in 1988–89. Since 1990, all the scientific activities/observations have been carried out at Maitri, although the Dakshin Gangotri site is still used as a summer camp.

The information in this section is mostly about Maitri, however, comparisons with Dakshin Gangotri, or information about the latter station, are provided where relevant.

7.5.7.1                          Orography and local environment of Maitri

Maitri is located in the central part of Schirmacher Range, Dronning Maud Land, East Antarctica (see Figure 7.5.7.1.1). This oasis is about 16 km long stretching in an east–west direction between 70º 44´ 30″ S to 70º 46´ 30″ S and 11º 22´ 40″ E to 11º 54´ 00″ E with a maximum width of about 2.7 km in the central part. The altitude of Maitri is 117 m above sea level. There is a big glacial lake (Priyadarshini Lake) in front of the station that provides water for all domestic purposes throughout the year.

The Schirmacher oasis forms a group of low lying hills about 50 to 200 m (160 to 650 ft) high. One such small hill is located in the vicinity of Maitri by the side of Priyadarshini Lake. It is about 500 m away from the station. There is a small hillock of conical shape popularly known as SHIVA–LING surrounded by continental ice located west of Maitri at a distance of about 2.5 km. A wall of glacier ice (snout) about 6 to 7.5 m high is located towards the south at a distance of about 500 m approximately in the east – west direction. During the summer months the melt from the northern periphery of the continental ice sheet cascades gently down over the exposed bedrock.

The scientific station of Novolazarevskaya (see Section 7.5.8) is situated towards the southwest about 4 km from Maitri while "Gorge Foster", the German scientific station, is located 5 km away from Maitri towards the south–southwest. The Schirmacher Range lies in between the Wolthat Mountains about 80 km to the south and the tip of the shelf ice that is about 100 km to the north. The northern boundary of the Schirmacher oasis has an abrupt and steep fall towards the shelf ice.

7.5.7.2                          Operational requirements and activities relevant to the forecasting process

The main objectives of the meteorological programme are as follows:

·                         to build up a data set for climatology of the Antarctic;

·                         to conduct research on various aspects of weather at Antarctica and it’s influence on global weather in general and weather over the Indian sub–continent in particular;

·                         to organize an observational programme for the study of radiation budget, ozone hole phenomenon etc;

·                         to arrange real–time transmission of main hours (6 hourly) synoptic observations on the GTS.

Meteorological Observations

Along with synoptic observations, the meteorological programme also includes the study of radiation, surface ozone, atmospheric turbidity etc. Regular reception of gridded APT satellite pictures in the infra–red and visible channels from polar orbiting satellites (NOAA) and analysed weather charts from Pretoria (South Africa) help in monitoring and forecasting of weather systems approaching and affecting the station.

The facsimile equipment on board the ship (MV Polar Bird) is also of great help in monitoring the weather charts transmitted from India and Pretoria (South Africa) during the route from India (Goa) to Antarctica. The autorecorder data of temperature, wind speed, wind direction, pressure, global solar radiation and surface ozone is regularly tabulated and computed. The continuous record of surface meteorological observations at Maitri indicates that the weather over Antarctica experiences large seasonal variations.

Upper–air Observations

The upper–air programme presently consists of Radiometer Sonde ascents (RMS) and ozonesonde ascents.

Weather Sensitive Activities at the Station

The main weather sensitive activities at the station are helicopter operations during the summer period and convoy activity between station and ice shelf, almost throughout the year.

Weather in Antarctica is subjected to frequent and sudden changes. The fast deterioration of fair weather is common here. Drifting and blowing of snow and high wind gusts are typical of Antarctic conditions during blizzards. In severe cases it leads to zero visibility conditions. Helicopter operations are carried out for transportation of equipment and scientists for scientific activities. Before every helicopter flight from ship to the station and back, prevailing weather conditions are communicated to the pilot. Pilots are generally most interested in wind speed/wind direction, visibility, cloudiness etc. over the station.

Snowfall is observed mostly during the summer period but its intensity is very light and it is in the form of snowflakes (generally star shaped). As such snowfalls may not affect the field activities of the station.

From April to September the number of bad weather days increases and most of them are either due to blowing or drifting of snow. Under these conditions, working outside the laboratory is restricted depending upon the intensity of the bad weather. But during such periods, various in–house activities are arranged.

Local weather forecasts/outlooks for 24–48 hours are being provided regularly for day to day planning and execution of station maintenance, scientific and other logistic activities. The day’s weather summary is also displayed at the station for general awareness of weather to expedition members.

7.5.7.3                          Data sources and services provided

A meteorological observatory at Maitri was established in January 1990. A Stevenson screen and two wind masts were installed in front of the station. A view of the meteorological observatory is shown in Figure 7.5.7.2.1. Self–recording instruments for continuous recording of pressure, temperature, wind speed and direction, surface ozone and global solar radiation are kept inside the lab and the sensors installed outside. An APT recorder, radiosonde ground equipment, fax recorder are also kept in the laboratory. The APT omni–directional antenna and helical antenna for ozonesonde/radiometer–sonde are erected on the top of the main building.

The main source of Maitri surface data, such as temperature, pressure, wind speed and wind direction, weather (past and present), visibility, cloud type and amount etc. is the routine three hourly synoptic observation. In addition to manual observations every three hours, continuous recording of wind speed and direction, atmospheric pressure, air temperature, diffuse and direct solar radiation, is being carried out with the help of self–recording instruments. Hourly measurement of atmospheric turbidity during the summer period and for the available sunshine period during winter is done through sun–photometer. During periods of significant weather such as blizzards, hourly observations are also recorded.

For upper–air data such as temperature, pressure, humidity, vertical ozone distribution etc. the upper–air ascents from radiosondes, ozonesondes, radiometer–sondes etc. are taken weekly, fortnightly, or more frequent, as required.

Maitri is in a valley between continental ice and shelf ice, located on a narrow hill range that is 17 km long and 4 km wide, east–west oriented. Due to its location and magnetic field disturbances disabling HF communication during winter, it becomes almost impossible to receive the analysed weather charts transmitted from the Pretoria weather service. These weather charts are mainly aimed at catering to the needs of ships in southern waters: there is no analysis of systems over the Antarctic continent.

7.5.7.4                          Important weather phenomena and forecasting techniques used at the location

General overview

Maitri and Dakshin Gangotri are affected by the eastward moving depressions that are synoptic scale frontal systems. These systems move in the circumpolar trough zone that lies between 60 and 66º S meandering north and south between seasons. The large amplitude cloud bands in association with these systems move across the station, producing dramatic variation in cloud cover. The cyclonic circulation associated with these low–pressure systems is frequently also seen on the 500–hPa chart. These systems bring warm and moist air to the coastal areas of the Antarctic continent from northern latitudes. Therefore, when a depression approaches the station, pressure starts falling continuously and temperature starts rising. The rise in temperature, which can be of the order of 10ºC during a blizzard, is also due to the fact that the low level inversion is broken due to turbulence caused by increase in wind speed.

The pressure gradient in the field of the system is very steep and consequently produces very strong winds. There may or may not be precipitation. It is very difficult to judge whether there is precipitation or not due to drifting snow. After the system moves away, the opposite sequence of changes occur: pressure increases (often steeply); temperature falls; wind becomes light or calm; and the sky clears.

On some occasions when small lows move at relatively higher latitudes, the skies are overcast with stratus and calm or light wind prevails. Such situations result in heavy snowfall at the station.

It has been observed that the intensity of blizzards is greater and their duration longer at Dakshin Gangotri than at Maitri, for the simple reason that the former location is closer to the coast.

There is little mesoscale activity affecting the station.

Surface wind and the pressure field

Maitri and Dakshin Gangotri Stations lie between the high–pressure region centred about the South Pole and the circumpolar trough of low pressure roughly along 63º S. Therefore atmospheric pressure at the stations is influenced by the relative position and strength of these features.

At Maitri the seasonal variation in pressure shows a trend of alternate rise and fall with highest values in summer and winter and lowest values in autumn and spring (Figure 7.5.7.4.1 (in Appendix 2)). Day to day variation in pressure can be very dramatic.

The surface wind regime at Maitri is characterized by alternating spells of strong wind and light wind or calm. The duration of these spells varies considerably from a few hours to several days. The mean daily wind speed varies between 5 and 10 m s^–1 (~10 and 20 kt). The wind maximum recorded in each month varies between 28 and 41 m s^–1 (~55 and 80 kt).

A study of wind data collected at Dakshin Gangotri, during 1987, revealed that on 65% of the days average wind speed exceeded 5 m s^–1 (~10 kt) and on 30% of the days the mean daily wind speed exceeded 10 m s^–1 (~20 kt); 15% of the daily maximum wind speed exceeded 20 m s^–1 (~40 kt). At this station strong wind is invariably from the east–southeast direction whereas at Maitri strong wind is from the southeast. Figure 7.5.7.4.2 (in Appendix 2) shows the monthly mean wind speed at Maitri while Figure 7.5.7.4.3 (in Appendix 2) shows the mean–monthly days of blizzard.

Wind direction is a significant feature of weather both at Dakshin Gangotri and Maitri. It serves as a sure indication of the type of ensuing weather. A wind rose for Maitri based on 1992 data is shown in Figure 7.5.7.4.4 (in Appendix 2).

The most predominant direction at Dakshin Gangotri is east (52%) while at Maitri it is southeast (28.5%). Sector–wise it is the east–southeast sector (090 –135º) that accounts for 80% of wind directions at Dakshin Gangotri and 56% at Maitri. The next important sector is the south (160 – 200º).

Based on the synoptic situations that give rise to different wind directions at Maitri, five different groupings can be made that are explained in terms of synoptic influences as follows:

·                         East to south winds (56.0% of occasions) result from approaching depressions from the west. As long as the station is under the influence of these systems the wind direction remains constant in this sector.

·                         If the depression recurves to northeast after crossing the station’s longitude the station experiences north–northeast to east–northeast or easterly winds (1.6% of occasions).

·                         Wind directions from the southwest or west occur (2.3% of occasions) when a low–pressure system crosses the continent radially and move over the continent to the south of the station's location.

·                         Southerly winds (28.6% of occasions) are due to katabatic winds driven by the polar anticyclone.

·                         Winds from the northwest or north (2.4% of occasions) are due to the passage of a high–pressure ridge across the station.

As discussed above there exists a close relation between the wind direction, speed and the synoptic situation. Hence it is not too difficult to predict the local winds at Maitri Station. If analysed weather charts are available, one may attempt to predict the wind speed. As a rule of thumb it is noted that in the case of depressions 4 to 5 m s^–1 (~8 to 10 kt) can be counted for every closed isobar.

Katabatic winds are characterized by high directional constancy but show large variations in speed: their direction at Maitri is invariably southerly, since the elevation increases in that direction.

Katabatic winds are more frequently experienced at Maitri than at Dakshin Gangotri as it is located about 80 km south of Dakshin Gangotri at the margin of the polar ice cap. While the frequency of katabatic winds at Maitri is about 28%, at Dakshin Gangotri the frequency is about 10%. Although katabatic winds occur throughout the year; their frequency is a maximum during winter season from April to August, followed by spring and autumn. Their frequency is least in summer (November–January). During autumn and spring katabatic winds set in by late evening (1800 hrs) and continue to morning (0600 hrs). But during winter these winds occur at any time of the day. The speed of katabatic winds may vary from 3 to 15 m s^–1 (~6 to 30 kt), and shows large variations frequently over short time intervals. Sudden onsets, with the wind speed jumping from almost calm to 12 to 15 m s^–1 (~25 to 30 kt), and equally sudden cessations (lulls) are common.

Upper wind, temperature and humidity

No specific information on forecasting has been obtained.

Clouds

Most cloud forms are a variation of stratus, although stratocumulus is often seen in summer. Cumulus cloud is very rare but cirrus cloud is often widespread and forms at much lower levels than in temperate regions. Reliable cloud observations are very difficult during blizzard conditions since the sky invariably remains obscured.

Visual cloud observations made during 1987 at Dakshin Gangotri showed that mean daily cloud cover was a maximum in autumn followed by summer. It was significantly less in spring and winter. The sky was overcast on 13% of the days, cloudy (4 to 7 oktas) on 26% of the days and partly cloudy (1 to 4 oktas) on 46% of the days. Seven percent of the days were absolutely free from cloud when fine weather prevailed. The sky was obscured on 7% of the days mostly due to blizzards. In the peripheral regions of Antarctica it frequently happens that the sky is clear for most of the days but gets “ engulfed” by clouds in a short time or vice versa. This is because of the frontal nature of the weather systems and associated cloud bands.

The cloud types most commonly observed are stratus (Stratus fractus), altostratus (Altostratus translucidus and Altostratus opacus), altocumulus (Altocumulus translucidus and Altostratus duplicatus) and cirrostratus (Cirrostratus fibratus and Cirrostratus nebulosus).

There are several forecasting approaches to cloud forecasting that may be taken:

·                         Uses of Satellite Imagery and other data: At Maitri Station satellite cloud imagery transmitted by NOAA satellites is received. These images, in conjunction with ground observations of cloud cover and type, are used for prediction of local weather. As mentioned earlier, cloud coverage over the station is determined by the movement of cloud–bands, which often originate in mid–latitudes and are present for some time. Hence satellite cloud imageries are of great help in monitoring the cloud coverage.

·                         Clear sky compared to overcast conditions: Irrespective of the season, clear sky can exist over Antarctica. From Table 7.5.7.4.1 (in Appendix 2) it may be seen that about 30% of days in year, winter or summer will be clear or near clear at Maitri. Generally speaking periods of clear sky are associated with calm or light winds, although even during blizzards the sky may be clear above the blowing snow.

·                         Prediction of clear sky conditions: A general understanding of the weather systems at Maitri will greatly help in predicting a clear sky at Maitri. A ridge, a col region or a region without any significant pressure variations and gaps between the cloud bands of low–pressure systems, and long distance between two pressure systems gives us scope to predict predominantly clear skies.

Visibility: blowing snow and fog

·                         Blowing snow: Blowing snow is quite a common occurrence and is encountered in all the months. It is associated with blizzards or snowstorms and often reduces horizontal visibility considerably. In common with other areas of Antarctica, drifting snow and blowing snow occur in the Maitri and Dakshin Gangotri area in a sequence controlled by the wind speed and other antecedent factors, such as snowfall and temperature. Usually surface snowdrift is initiated at a wind speed of about 10 m s^–1 (~20 kt). As the wind speed increases intensity of drift increases and at a speed of about 18 m s^–1 (~35 kt) blowing snow is initiated. The intensity of blowing snow increases with further increase in wind speed. The visibility progressively decreases and becomes zero at a wind speed of about 36 m s^–1 (~70 kt). However, these threshold wind speeds may be reached earlier if there is recently fallen snow. During winter, due to very low temperature initiation of drift and blowing of snow may occur at relatively higher wind speeds as compared to other seasons given the same surface snow condition.

·                         Fog: Fog is not common at Dakshin Gangotri. During 1987, there were 13 days with fog; out of which 6 days were in the summer months of December and January. The remaining fog days occurred in the other seasons. Advection fog is the most common, although shallow radiation (ground) fog occurs in the evening (1600–1800 hours local time) in the summer months. Advection fog is generally thick, reducing the visibility to zero on some occasions and lasting for 3 to 6 h. The occurrence of fog at Maitri is even rarer (about 3 days in a year) and is mostly in the summer month of December.

Surface contrast including white–out

No specific information on forecasting has been obtained.

Horizontal definition

Maitri enjoys good horizontal definition as it has shelf ice in the north, a gradually rising valley in the east, an east–west oriented and steeply rising glacier front in the south, and a three peaked hill in the west, defining the horizon. If a person regularly moves around on fair weather days it becomes difficult for him to be lost in blizzards as he/she will be familiar with the environmental objects and their bearing to the station.

During calm days, with intense temperature inversions over the continental ice, or over the shelf ice, the surface appears lighted causing mirages and extending the general horizon, when compared to that normally seen on other days. During December and January one can see icebergs in the sea (north of station) that is about 100 km away. There are reports of sighting anchored ships from the glacier near the station. On a late evening during December 1993 one could see the illusion of the northern ice shelf getting lifted like a wall when viewed from the glacier. Helicopter pilots have not reported any difficulty in flying due to mirage effect or temperature inversions.

Precipitation

Precipitation is usually in the form of snow, although a shower was reported once during February in 1996. During December 1997 there was an occasion when the snow particles turned into water drops on touching the ground and evaporated. Such precipitation is called snowfall of solid precipitation, irrespective of their structural differences and is classified as “snow” for meteorological recording purposes.

Snowfall occurs in two typical forms:

·                         associated with polar depressions;

·                         as more conventional snowfall with calm or light winds.

Snowfall associated with polar depressions generally cause blizzards due to high winds associated with the low–pressure systems. The snowfall will be generally horizontal (almost), relatively warm, and visibility falls below 10 metres. Blizzards also occur due to heavy blowing snow even without normal snowfall. Hence it becomes difficult sometimes to say whether there is snowfall associated with a particular blizzard or not. Hence snowfall associated with blizzards is not treated as conventional snowfall for meteorological accounting.

Conventional snowfall can be easily identified due to its occurrence and nature. Calm or light wind, snowfall accumulation, no significant temperature change and vertical precipitation are some of the salient properties associated with a conventional snowfall. Under a simple microscope, one can observe the crystalline structure of the snow grains. The fresh snow will be generally soft and loosely packed with very low density (snowfall density of accumulated snow during a blizzard will be almost 5 to 10 times that of fresh snow due to light packing by wind).

During summer months the low–pressure systems move far north of Maitri causing a good number of clear days. During winter cols, ridges and high–pressure zones residing over or near the station give a fair indication of light/calm winds. Micro–barograph data help to locate these systems in a broad patch of featureless cloud, generally detached or very far away from a low–pressure system. When such a system is seen approaching the station, snowfall can be predicted. By experience one should assess the type of cloud (low/medium/high) using the “colour” with reference to sea or ice surface. If the temperature is “warmer”, it indicates the capacity of the cloud to give precipitation. Continuous observation of the clouds also gives the observer an idea of what types of cloud gives precipitation.

In summer ragged cumulus clouds are seen, but they rarely give snowfall. Very fast moving stratus and stratocumulus have given “passing showers of snow” some times. Thick altostratus clouds covering a large area have produced large amounts of heavy snowfall during winters. Such clouds generally resulted when the cloud organisation got disturbed and disorganised when they crossed the “cold land” of Antarctica during spring and autumn months.

Snowfall prediction is of importance for stations on the shelf ice where there is a chance that items like food dumps, fuel dumps or scientific instruments installed on ice, small vehicles and tools etc. are likely to be lost after intense snowfall. At Maitri such problems are never experienced except that open servicing of vehicles and construction activities need to be suitably warned to enable them to take precautionary measures. Though there were days when the accumulated snowfall lasted for a week at Maitri after snowfall, most snowfall accumulation either evaporated or was absorbed by land in about 2 days. A snow gauge/rain gauge was installed in the summer of 1997 at Maitri.

Temperature and chill factor

The temperature gradually falls from January to July, but rapidly rises up to December. July is generally the coldest month. Annual average temperature is around –10ºC at Maitri though highest temperature goes up to +10ºC and lowest up to –35ºC.

Icing

No specific information on forecasting has been obtained.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

Hydraulic jumps have not been reported at Maitri.

Sea ice

No information provided for Dakshin Gangotri – not relevant for Maitri.

Wind waves and swell

No information provided for Dakshin Gangotri – not relevant for Maitri.

7.5.8                                Novolazarevskaya Station  

7.5.8.1                          Orography and the local environment

The Novolazarevskaya Station (70° 46' 04” S, 11° 00' 54” E, 102 m AMSL) (see Figure 7.5.1) is located at the extreme southeastern tip of the Schirmacher oasis approximately 80 km from the Lazarev Sea coast. An ice shelf with a slightly undulating surface resting against an ice cap extending north of the station in the vicinity of Leningradsky Bay. From the south, there is a continental ice sheet slope.

The oasis presents a bedrock area elongated in a narrow strip around 17 km long and 3 km wide in the direction from west–northwest to east–southeast. Its relief is typically hillocky with the highest hills up to 228 m in elevation. There are up to 180 lakes in the Oasis. The ice cover on the lakes typically persists in summer.  Melting, however, occurs on some lakes.

The oasis climate has predominantly continental characteristics. It is mainly formed depending on the intensity of solar radiation. Much of the oasis area is characterized by the absence of continuous ice cover not only in summer but also in winter. Moraines outcrop to the surface of glaciers surrounding the oasis. In winter, moraines and hillocky relief are partly snow–covered.

7.5.8.2                          Operational requirements and activities relevant to the forecasting process

The station was opened on January 18, 1961. There is a runway for ski– and wheeled– aircraft located some 15 km south of the station on the ice sheet surface at 500 m above sea level. The runway has dimensions of 1,200 m by 60 m and the landing direction of 114º.

A station re–supply visit occurs once per season (in January – March) with the resupply vessel anchored some75 km from the station.

7.5.8.3                          Data sources and services provided

No specific information has been obtained.

7.5.8.4                          Important weather phenomena and forecasting techniques used at the location

General overview

The atmospheric circulation pattern over Dronning Maud Land is in general as follows. In the west and east of the Dronning Maud Land, two high–pressure ridges of low mobility extend in the meridional direction with the axes along 8–9^o W and 50^o E. These ridges probably combine above the inland plateau. A quasi–stationary depression in the coastal zone between the ridges (4 to 37^o E) is maintained by oceanic depressions intruding from the north around 20–25º E. Two branches of the meridional cyclone trajectories almost converge here, the eastern branch of the Falkland and the western branch of the South–African trajectories. The cyclones of the eastern branch of the Falkland trajectory move along the coast influencing the weather in the oasis to a smaller extent, whereas along the western branch of the South–African trajectory, the cyclones move almost along a meridian southward. They are deeper and produce a significant influence on the weather character in the coastal areas of the Dronning Maud Land.

The Schirmacher oasis is also subjected to the influence of the peripheral area of the Antarctic High that gives clear frosty weather with dominating katabatic winds. Winter (April–September) is relatively "mild" in general but with strong winds, frequent storms and snowstorms with snowfall. More than 70% of annual precipitation falls out. During the anticyclonic situation, frosty weather sets in, winds attenuate and the air temperature drops and air dryness increases. The atmospheric pressure is high and the absolute humidity is the least for the year. The frequency of occurrence of middle clouds and clear weather is high.

In spring (October–November), the atmospheric pressure sharply decreases, winds attenuate and the air temperature and humidity increase considerably although the amount of lower clouds decreases. The frequency of occurrence of upper clouds increases. Precipitation is still abundant. Active evaporation and melting of winter snow begins. In mid–October, the above zero temperatures on the snow–free soil surface are recorded.

In summer (December–January), the atmospheric pressure is the highest. There is relatively high temperatures and air humidity. Cloudiness (especially low clouds) increases and the frequency of clear weather decreases, the winds are comparatively weak. Snowfall is rare and precipitation is insignificant. There is rapid snow and ice melting and intense drainage of melt water from the oasis to the ice shelf.

Autumn (February–March) is characterized by decreasing air temperature and humidity and increasing total cloudiness with dominating middle clouds. Winds become stronger although snowfall is still rare and precipitation amounts are small. The atmospheric pressure slightly decreases, but remains high. Melt water in the oasis freezes and ice cover forms on the lakes.

In view of the remoteness of the Novolazarevskaya Station from the coast, the probability of occurrence of mesolows is very small, especially in winter when the mesoscale cyclogenesis area moves northward to the drifting ice edge.

Surface wind and the pressure field

Winds in the Schirmacher oasis are naturally weaker than at the coast. The average annual wind speed at Novolazarevskaya Station is 10.2 m s^–1 (~20 kt) Table 7.5.8.4.1 (in Appendix 2). The maximum wind speed is observed in winter with the minimum in summer. June is distinguished by the largest average wind speed (12.8 m s^–1 (~25 kt)). There are 196 days with strong winds on average, for a year. December and January are characterized by the lowest average wind speeds, with the wind speed in January being 2–5 m s^–1 (~ 4–10 kt) in more than 45% of all cases.

One maximum (in the morning and at night during the intermediate seasons) and one minimum (in the evening) are observed in daily wind speed variations.

An analysis of the frequency of occurrence of wind directions revealed that cyclonic easterly–southeasterly winds had the largest intensity (with the frequency of occurrence of 34% and a speed of 12.8 m s^–1 (~25 kt)), then the southeasterly winds followed (with a frequency of occurrence of 20% and the speed of 12.8 m s^–1) and the katabatic south–southeasterly to south–southwesterly winds (with a frequency of occurrence of 26% and a speed of 10.3 m s^–1 (~20kt)) were third most common. The frequency of occurrence of winds from the other 11 directions was 13% and the average speed 3.3 m s^–1 (~ 6.5 kt). The main wind types correspond to the main weather types. Cyclonic weather is accompanied by cyclonic easterly–southeasterly winds while the anticyclonic weather is characterized by katabatic south–southeasterly to south–southwesterly winds. In winter, the atmospheric pressure decreases with changing wind type and the difference in weather conditions is more pronounced with cyclonic and katabatic winds.

The average annual station–level air pressure is very low being 975.5 hPa. This is the lowest atmospheric pressure for all coastal Antarctic stations. Annual variations of atmospheric pressure, similar to the other Antarctic stations have two maximums (in June and February) and two minimums (in April and October) (Table 7.5.8.4.2(in Appendix 2)).

The inter–annual amplitude of atmospheric pressure in the station area varied between 11 to 28 hPa with the absolute amplitude changing from 62 to 73 hPa.

At the coastal Antarctic stations exposed to the action of katabatic winds, the atmospheric pressure is poorly related to other meteorological elements. The wind speed typically increases with decreasing pressure, but at its maximum values, the wind also increases.

Upper wind, temperature and humidity

No specific information on forecasting has been obtained.

Clouds

Total cloudiness is equal on average to 4.6 oktas for the year. The highest cloudiness occurs in summer (4.9 oktas). The least total cloudiness was recorded in winter (4.5 oktas) with the minimum monthly mean observed in September 1965 (2.2 oktas). The lower–level clouds are insignificant comprising 0.8 oktas on average for a year. The least values are observed in summer (1.1 oktas). The minimum values of lower clouds occur in spring (0.5 oktas).

The middle–level clouds prevail above the station. These are altocumulus and altostratus (with the frequency of occurrence of 42%), their largest frequency observed in autumn and the least in winter. The high–level clouds are mainly cirrus, being observed in 26% of all observation cases. In the annual variations, the frequency of occurrence of these clouds is minimum in autumn and winter and a maximum in spring and summer.

The lower–level clouds are predominantly nimbostratus clouds and stratocumulus clouds are rare above the stations, their frequency of occurrence for the year comprising 9%. Clear weather prevails in winter and in general over the year, the frequency of occurrence comprises 21%.

Visibility: blowing snow and fog

No specific information on forecasting has been obtained.

Surface contrast including white–out

No specific information on forecasting has been obtained.

Horizontal definition

No specific information on forecasting has been obtained.

Precipitation

Precipitation at the Novolazarevskaya Station is mostly in the form of snow. Rime and hoar frost, tapioca snow or wet snow, were rarely recorded. The annual amount of precipitation is 309 mm.

Precipitation is almost exclusively brought by cyclones and accompanies a typically cyclonic pattern with low atmospheric pressure, elevated air temperature and humidity, strong wind and almost continuous and significant low clouds. Snow falls mainly from stratus clouds whose frequency of precipitation is 45%, or from high stratus clouds (with the frequency of precipitation of 39%).

In the overwhelming majority of the cases, the cyclonic easterly–southeasterly winds or transient southeasterly winds (with the frequency of occurrence of 75 and 20%, respectively) were observed when this occurs. Precipitation was most often recorded during snowstorms with strong winds. For example, in 67 cases of snowfalls in July–September the average wind speed was 18–23 m s^–1 (~35–45 kt) (at the average monthly wind speed of 11–14 m s^–1 (~20‑27 kt)) while the air temperature was 3–5ºC higher than monthly means. On average for a year, there are 72 days with snowfalls in the station area. The largest amount of precipitation falls out in winter and spring with the lowest precipitation in summer and autumn.

Temperature and chill factor

Table 7.5.8.4.3 (in Appendix 2) shows mean–monthly temperatures for Novolazarevskaya Station. The warming influence of the oasis is expressed in a relatively higher air temperature. The average annual temperature is about –10ºC i.e. higher than at the nearest coastal stations. The average temperature oscillations from year–to–year are insignificant, within 1ºC.

The winter air temperatures are observed already in April and persist around –14 to ‑15ºC during the following months. By the temperature regime, the winter season continues for 6 months. July–August is the coldest period. Summer in the oasis is relatively warm and continues for two months – December and January. The maximum temperatures and the highest minimum temperatures during the year are typically observed in the summer months. The highest temperatures are recorded between the second 10–day period of December and the second 10–day period of January, i.e. during the summer solstice. Usually at this time in the oasis, rapid snow and ice melting occurs, numerous relief depressions are filled with melt water and there is intense discharge from the lakes to the ice shelf.

Based on the temperature regime the duration of intermediate seasons is two months: October–November (spring) and February–March (autumn). Average temperatures in spring are –10.2ºC and in autumn –6.4ºC.

Daily air temperature variations at the station are typical, with the maximum at midday and the minimum at night. The non–periodic air temperature oscillations are related to changes in the synoptic conditions. Dramatic cooling events in winter occur with the onset of anticyclonic weather and very light winds.

The absolute air humidity partial pressure, on average for a year, is 1.6 hPa, its values from year–to–year varying only by 0.1 hPa. The largest air humidity partial pressure is in summer (3.2 hPa) and the smallest in winter (1.0 hPa). The extreme humidity values at the observation times reach almost 5 hPa in summer and 0.2 hPa in winter. Relative humidity on average for the station was 52%. The changes of its average annual values ranged between 48 to 56%. Complete air saturation with moisture (100%) was recorded comparatively frequently with passing cyclones bringing moist warm air typically with snowfall from the ocean. The driest air is transported by katabatic winds.

Icing

No specific information on forecasting has been obtained.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

No specific information on forecasting has been obtained.

Sea ice

The recurring polynya in Leningradsky Bay spanning 10–14º E is the most remarkable and important feature of ice conditions in the coastal area of the Novolazarevskaya Station. This is one of the most stable Antarctic polynyas persisting in most years almost throughout the year.

The development of polynyas typically begins in September being due to the break–up of the marginal land–fast ice zone whose maximum width in this area comprises 40 km. At first, the polynya is mainly localized under the northwestern tip of the protruding Lazarev Ice Shelf. Then with land–fast ice decay, following the break–up “wave”, it extends in the general west–southwest direction and by March typically covers the entire Bay with an area of up to 5,000 km².

However, the inter–annual variability of the final decay of local land–fast ice and the corresponding maximum polynya dimensions of approximately 150 by 35 km is around 4 months from January to April.

North of the polynya there is a belt of close drifting ice that decreases by the end of summer in February up to 55 to 110 km (~30–60 nm), on average, disappearing completely in some years.

Autumn ice formation begins in the polynya area in late February–early March, but its intensity is weak up to mid–March. In addition, new ice produced in the polynya in March–April is completely exported from the Bay northward by the dominating offshore winds towards the southern edge of the belt of residual drifting ice.

The formation of new land–fast ice begins on average only in late April–early May being interrupted by frequent breaks at its margins. As a result, the final freeze–up of Leningradsky Bay signifying establishment of land–fast ice up to 40 km wide and disappearance of the polynya is mainly observed only during August. The average land–fast ice width at the time of the spring–summer break–up is about 1.5 m with prevailing snow cover depth of 30 cm. The land–fast ice thickness increases from 1 m near the edge to more than 2 m near the glacier barrier in connection with the intense frazil ice formation here.

Wind waves and swell

No specific information on forecasting has been obtained.

7.5.9                                Inland of Syowa (Asuka, Mizuho, Dome Fuji)  

Three stations, Asuka (71^o 32´ S, 24^o 08´ E), Dome Fuji (77^o 19´ S, 39^o 42´ E) and Mizuho (70^o 42´ S, 44^o 20´ E), are located inland of Syowa Station (see Figure 7.5.1 and Figure 7.5.9.1). These stations have been used for over–wintering, but at present, are used as summer–only or temporary stations. Over–wintering has taken place during February 1987 to November 1991 at Asuka, during January 1995 to January 1998 at Dome Fuji, and from June 1976 to October 1986 at Mizuho.

7.5.9.1                          Orography and the local environment

·                         Asuka Station is located in East Dronning Maud Land, close to the Sor Rondane Mountains, at a height of 930 m AMSL. It is about 120 km from Breid Bay, Princess Ragnhild Coast. The former Belgian and Dutch station, Roi Baudouin was located in this area near the coast on an ice shelf. (Although noticeably west of Syowa, Asuka is included in the group of Japanese operated stations).

·                         Mizuho Station is located at a height of 2,230 m AMSL.

·                         Dome Fuji Station is located 1,000 km from the coast at an altitude of 3,810 m AMSL – the highest station in the Antarctic – and is used mainly for deep ice core drilling.

7.5.9.2                          Operational requirements and activities relevant to the forecasting process

The stations are operated on a summer–only basis as required.

7.5.9.3                          Data sources and services provided

During wintering at each station synoptic meteorological observations have been collected. However, all observations were made when the stations were operating as research bases, except for 1990 and 1991 at Asuka Station, when the Japan Meteorological Agency conducted the routine base observation programme. In addition to these synoptic observations, aerological observations were also collected sporadically at the stations in some years. Measurements of temperature and wind profiles using a 30 m tower were made at Mizuho Station during the Polar Experiment (POLEX) South project. Those data were reported in publications from JMA and the Japanese National Institute of Polar Research (NIPR) (see http://www.nipr.ac.jp/). The POLEX South project took place during 1979 and 1981 and included extensive observations of the surface radiation budget, surface boundary layer profiles and conditions in the katabatic wind zone.

Extensive field observations for geology and geomorphology were made at Asuka Station during five summer seasons. At Dome F, extensive atmospheric observation programmes were carried out under the project "Atmospheric circulation and material transfer in the Antarctic" in 1997.

7.5.9.4                          Important weather phenomena and forecasting techniques used at the location

General overview

As discussed below, Mizuho and Asuka are located on or close to the steep continental slope and their climates are dominated by katabatic winds. Dome F on the other hand has a climate typical of the inland high plateau.

Monthly summaries of conditions at each station are given as follows:

·                         Asuka Station – in Table 7.5.9.4.1 (in Appendix 2);

·                         Dome Fuji – in Table 7.5.9.4.2 (in Appendix 2);

·                         Mizuho Station – in Table 7.5.9.4.3 (in Appendix 2).

Surface wind and the pressure field

·                         Asuka Station. Since the station is located in the katabatic wind zone and close to the mountains, its meteorological conditions are strongly affected by downslope winds. The annual mean wind speed is more than 12 m s^–1 (~23 kt) and even the monthly mean exceeded 15m s^–1 (30 kt) for 6 months during 5 years of observation. This high frequency of strong winds often gives deep blowing snow and poor visibility.

·                         Dome Fuji. Since the station is on the "dome" of a high plateau on the ice sheet, there is no predominant surface wind direction, as is found in the katabatic wind zone. However, the wind speed is stronger than expected, with an annual mean of 5.8 m s^–1 (~11 kt).

·                         Mizuho Station. The station is located on the slope of the continental ice sheet and the climate is characterised by strong katabatic winds. The average wind speed in winter exceeds 12 m s^–1 (~23 kt) and the annual average is 11 m s^–1 (~21 kt) and is predominantly easterly (more than 90 % of the wind directions reported are from between east–southeast and east–northeast.

Upper wind, temperature and humidity

No specific information on forecasting has been obtained.

Clouds

Cloud amounts at Dome Fuji are low, especially during winter and only a few synoptic disturbances intrude into the inland area. However, pronounced blocking high episodes occur approximately once a month in winter, accompanied by abrupt increases of temperature, with a rise of more than 40ºC being recorded on one occasion.  More than one third of days during the year are clear.

Visibility: blowing snow and fog

No specific information on forecasting has been obtained.

Surface contrast including white–out

No specific information on forecasting has been obtained.

Horizontal definition

No specific information on forecasting has been obtained.

Precipitation

At Dome Fuji there are more than 300 days a year with precipitation (clear sky precipitation or diamond dust).

Temperature and chill factor

·                         Dome Fuji: Here temperatures are very low with the annual mean temperature for three years being –54.3^oC. At this location a typical coreless winter is seen with monthly mean temperatures of less than –60^oC being found from April to September. At Dome F, due to the location on the dome, the air temperature at the surface is higher than that at Vostok Station, although Dome F is at a higher elevation than Vostok.

·                         Mizuho Station. There is a strong surface inversion, especially in winter. However, normally, the lowest layer up to a few tens of metres above the surface is well mixed and the inversion is reduced in this layer owing to the strong wind.

Icing

No specific information on forecasting has been obtained.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

No specific information on forecasting has been obtained.

Sea ice

Not relevant at these locations.

Wind waves and swell

Not relevant at these locations.

7.5.10                            Syowa Station  

7.5.10.1                      Orography and the local environment

Syowa Station (69º 00' S, 39º 35' E, 21 m AMSL) is located on the East Ongul Island, 5 km from the Soya Coast in the eastern side of Lutzow–Holm Bay (see Figure 7.5.1; Figure 7.5.9.1 and Figure 7.6.1). The sea around the island is normally covered with fast sea ice and it is possible to travel around by over–snow vehicles. However, in some years, especially in summer to autumn, the sea ice around the station melts at the surface, breaks up and is blown out.

Shirase Glacier exists at the bottom of the Lutzow–Holm Bay, about 100 km from the station. This glacier is famous for its high rate of flow of about 2.5 km/a.

7.5.10.2                      Operational requirements and activities relevant to the forecasting process

Syowa Station is the centre for all the activities of the Japanese Antarctic Research Expedition (JARE). Inland traverses to Mizuho Station (70º 42' S, 44º 20' E, 2230 m), Dome Fuji Station (77º 19' S, 39º 42’ E, 3810 m AMSL), the Yamato Mountains, and the surrounding area, start from Syowa Station, or the S16 point that is a nearby depot on the ice sheet. Research expeditions to the coastal bare rock area and also sea ice traverses are made from Syowa. Weather forecasts are necessary for each of these operations.

The JARE operates two single engine aircraft, a Pilatus Porter PC 6, and a Cessna 185A Sky wagon, at Syowa Station. Aviation forecasts are required for these aircraft operations during summer and winter.

The research vessel Shirase, equipped with three helicopters, supplies Syowa with personnel, fuel and goods, once a year during December to February. The Shirase has its own forecaster on board; however, this person needs additional information from Syowa's meteorological office.

7.5.10.3                      Data sources and services provided

Routine meteorological observations are conducted at Syowa Station by the JARE, with five members from the Japan Meteorological Agency. Surface synoptic observations are conducted using an automatic meteorological system together with manual observations of present weather, visibility and atmospheric phenomena. Aerological observations are conducted with balloon launches twice a day at 0000 and 1200 UTC. Other special observations are also carried out on ozone and radiation.

At Syowa Station there is an Inmarsat link to Japan, to the NIPR and to the JMA. Analyses/forecast products from Tokyo Global Data Processing System Centre (GDPS, JMA) are transferred once a day. Observational data, SYNOP, TEMP CLIMAT and CLIMAT TEMP, are sent to the GTS through Meteosat DCP (Data Collection Platform), and those from other stations including AWSs are acquired from the GTS through Meteosat MDD (Meteorological Data Distribution). The latter system also provides orbit parameters of NOAA series satellite, ECMWF charts, and satellite imagery from Meteosat.

An APT satellite receiver is located at Syowa Station providing about 14 passes of AVHRR visible and infra–red imagery each day, and also an HRPT receiver providing about four to five AVHRR data and imagery passes each day. Information from the AWS at S16 is also used.

7.5.10.4                      Important weather phenomena and forecasting techniques used at the station

General overview

Because of the location of the station, the climate of Syowa Station is rather mild and maritime. Table 7.5.10.4.1 (in Appendix 2) provides a monthly summary of some of the key parameters. Katabatic winds, common to the continental slopes, are not necessary common to the station. Occasionally, blowing snow on the continental slope, due to the katabatic wind, is visible from the station but the katabatic wind does not itself affect the station. However, every now and then, the katabatic wind will reach Syowa, producing an easterly surface wind of about 7 to 10 m s^–1 (~ 15 to 20 kt). On the other hand, the eastward passage of low–pressure systems is rather common near the station: and the weather at the station is affected each time. When a low stops near the station, or moves southward and the inland over the continent, blizzards often occur at Syowa.

Summer conditions may be summarised as follows. In December and January, the possibility of clear or fair weather is more than 50%. Blizzards rarely occur at the station in these two months, but are more common in February. The inter–annual variation of meteorological parameters is large in this season. Monthly mean cloud amount during December and February was less than 4.8 oktas before 1987; however, it became more than 5.6 oktas during 1989 to 1993.

In autumn the likelihood of cloudy conditions or snow is more than 60% in March and April. Blizzards tend to occur in this season. The variation of the weather is periodic, with a frequency of about 7 to 10 days. The sea ice extent is a minimum in this season and open water is closest to the station. Sometimes, all the sea ice moves out and Ongul Islands, where the station is located, is surrounded by open water. Atmospheric circulation in the stratosphere also changes to a winter pattern.

In winter the variations of weather become relatively less and the possibility of clear days become higher. However, strong blizzards also occur in this season. The possibility of snowfall is highest and a drastic variation between clear weather and snow events occurs in July. The relative humidity is lowest in July and vapour pressure or absolute amount of water vapour is lowest in August: so much so that care is needed by staff to combat the dryness.

In spring, daylight hours become longer and the possibility of clear weather is higher in September: however, the possibility of major blizzards is also high in this month. The possibility of snowfalls is high in October, second only to July, and cloud amount is also high in this season. The loss of stratospheric ozone, (the ozone hole), is most pronounced in this season, and a decreasing trend of stratospheric temperature is clear from the last 20 years of record. The time of occurrence of warming of the stratosphere also shows a delaying trend in these years of record.

Surface synoptic observations are indispensable for forecasting, especially during periods when there are no new analyses or satellite imagery. Most of the surface observational data are from continuous recorders and can be used to interpolate between the analyses and prognoses. The local observations also reflect the local conditions directly, bearing in mind that the analyses or imagery are more on the synoptic scale. The observations are also used at Syowa to assess how well the numerical prognoses are performing.

Surface wind and the pressure field

When examining the surface pressure field from charts available at Syowa it should be noted that only a coarse distribution of pressure pattern is expressed in the Southern Hemisphere charts. Sometimes, there is no low analysed on the weather chart, even though a cyclonic vortex is seen in the cloud imagery. Also no frontal systems are depicted in numerical weather charts. The Southern Hemisphere analyses and prognoses show only the general fields, and it is necessary to use the cloud imagery to determine the actual weather conditions.

When there is a stationary low–pressure system to the north west of the station cloud systems arrive one after another, from the north or north east of the station as seen in the cloud imagery. However, large–scale blizzards are accompanied by low–pressure systems moving to the southeast to south–southeast. In other words, care should be taken when a low‑pressure system moves toward the station from the north–west and north–westerly winds strengthen at the 500–hPa level.

In summer, the extent of anticyclonic conditions over the continent dominates the weather condition at Syowa Station, with cloud cover, if any, caused by coastal lows. One needs to estimate the strength of anticyclone from the MSL prognosis to determine the relative effects.

Surface pressure decreases of 3 to 5 hPa hr^–1 or more might be accompanied by the development of blizzards. When the general pressure field is a high (high–pressure system dominates), blizzards tend to be minor. However, when the dominant pressure system is a low then a major blizzard will develop. When the low–pressure systems pass north of the station, the wind speed grows to the maximum when the surface pressure starts to increase.

In terms of wind direction, blizzards will occur with the surface wind direction only from the northeast or east–northeast. An easterly direction is also the normal katabatic wind direction. However, if the wind is forced by a low–pressure system, then the wind direction will usually change to the northeast.

Two types of increase in wind speed are seen when blizzards occur. Firstly, an approaching synoptic scale low will usually cause the wind speed to gradually increase. On the other hand, typically the wind speed will increase from light to strong, in a short time scale, such as thirty minutes, when a mesoscale cyclone approaches. This type of system occasionally approaches from the south–east.

With respect to katabatic winds, while these are not a major feature they can reach speeds of 10 m s^–1 (~20 kt) or more in the morning, but will invariably cease in the afternoon.

Upper wind, temperature and humidity

The twice daily aerological observations programme is indispensable for the forecasting process at Syowa. For wind speeds of 10 m s^–1 (~20 kt) or more, upper northerly winds bring bad weather to Syowa while southerlies bring good weather. So when the latter case has been observed and then a change occurs in the wind direction in the upper layers to northerlies then warm air is being advected southwards. The weather will change for the worse.

An increase of wind speed often suggests the approach of a low–pressure system: in particular with an increase of the 500–hPa wind in the direction of 300º one needs to be cautious. On the other hand it is difficult to say anything solely from the height of 500–hPa surface: one needs to monitor the variations in trends.

Looking at the value of the 500–hPa field in more detail it has been noted that, east of the 500–hPa trough there is generally a region of bad weather and east of a 500–hPa ridge is a region of fair weather. Generally speaking, when the trough at 500 hPa moves past Syowa, phenomena such as a blizzard will terminate.

Whereas in the mid–latitudes, low–pressure systems at the surface generally precede the 500 hPa by about 10 degrees in longitude when the low–pressure system approaches the Antarctic continent, the vertical slope of the vortex normally decreases. Usually, the surface pressure changes almost at the same time as the heights of pressure surfaces change up to 100 hPa, indicating that the vortex tube is standing nearly vertical.

There are two typical patterns in the 500–hPa height field affecting Syowa, viz, a "zonal pattern" and a "meandering or meridional pattern". In the case of a zonal pattern the strength of the continental high determines the weather conditions. If the high–pressure system over the continent extends to the coast near Syowa Station, fair weather occurs at the station. If the high does not extend to the coast, the weather will be worse, but not so as to be very severe. In the case of large–amplitude meanderings in the 500–hPa height field, the relative positions of the ridges and troughs are key factors. Under these situation, sometimes a low moves southwards from lower latitudes, near the east coast of Africa, and the weather becomes suddenly bad at Syowa. Periodic variations in the weather pattern are common; however, sometimes, a trough cannot move eastward due to blocking.

Clouds

Satellite imagery is indispensable for forecasting in the Antarctic, where surface observations are limited. It is helpful to analyse the cloud imagery together with the 500–hPa weather chart.

Vortex patterns of clouds with radii between 100 and 1000 km need to be watched. If the wind direction at the 500–hPa level is northeasterly, lows within 15º longitude east of the station may be steered southwest towards the station. If the wind direction at 500 hPa is northwesterly, lows to the west will approach the station, deepen and a major blizzard may develop. Normally, as the lows approach the upper clouds increase rapidly. If the 500–hPa wind direction is westerly, lows will approach from the west.

If there is a strong ridge west of the station, cloud systems from the northwest will be stopped by the ridge, and are liable to approach the station with the movement of the ridge and a blizzard may develop. There is a "graveyard" of lows west of the station: many lows approaching the continent lose their energy in this area and disappear within a few days.

Low level clouds (Sc or St) are liable to stay at the coast for more than a few days in some situations. Blizzards need not occur, but cloudy weather continues with precipitation, that affects aircraft operations. Aerological data show a moist layer confined below the low inversion. If the edge of a cloud layer moves northward, then the weather improves at once.

Sometimes cloud regions intrude inland, and bring a blizzard not only to Syowa Station but also to the inland Dome Fuji Station.

Visibility: blowing snow and fog

Strong wind may create drifting and blowing snow with low visibility. Blowing snow may be visible on the continental slope and suggests the existence of strong wind. While these winds may normally not reach Syowa itself great care should be taken, since, if they do, the visibility at the station can decrease from 1 km to 100 m within five minutes.

Surface contrast including white–out

No specific information on forecasting has been obtained.

Horizontal definition

No specific information on forecasting has been obtained.

Precipitation

No specific information on forecasting has been obtained.

Temperature and chill factor

Temperature is strongly related to wind direction. Northerly wind brings higher temperatures and southerly wind lower temperatures. Large temperature inversions may appear at the surface in light wind situations. It is not uncommon to have a sudden increase of air temperature of about 10ºC within three to four hours. This sudden increase of temperature is caused by the destruction of the surface inversion and might be accompanied by the development of a blizzard.

The dew point depression (T – Td) is smaller in situations involving falling snow compared to drifting snow events.

Icing

No specific information on forecasting has been obtained.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

No specific information on forecasting has been obtained.

Sea ice

No specific information on forecasting has been obtained.

Wind waves and swell

No specific information on forecasting has been obtained.