7.3.2        King George Island, South Shetland Islands 

7.3.2.3                          Orography and the local environment

King George Island is located in the South Shetland Islands at the tip of the Antarctic (see Figure 7.3.1 and Figure 7.2.1.1.1). It is the largest island of the archipelago and has dimensions of about 80 km by 30 km. Most of the island is covered by ice but bare, rocky peaks protrude at various places. The maximal thickness of the glacier ice is 326 m (~1,070 ft). The island is not very high and the peaks are only 600–700 m (~2,000–2,300 ft) in elevation (Figure 7.3.2.1.1) and the coast is deeply cut by many sheltered fjords and bays.

King George Island is orientated west–southwest to east–northeast and all the research stations are located on the south–facing side of the island, in the lee of the prevailing wind. The stations are generally near the coast and accessed via Admiralty Bay and Fildes Bay.

The Fildes Peninsula in the southwest corner of the island is flat and free of ice, and is where the island’s only airstrip (Marsh) is located. The north–western coast is washed by the Drake Passage waters, while its southeastern shore is under the influence of the currents in the Bransfield Strait. The Fildes Peninsula is formed from igneous rocks with the relief being typically small hills rising up to 150 m and with a lot of fresh water lakes. Most of the year the lakes are covered by ice with a thickness up to 1 m. In the Ardly Bay area fast ice usually forms in the middle of March with its thickness reaches 80–100 cm towards the end of March.

7.3.2.4                          Operational requirements and activities relevant to the forecasting process

King George Island is one the most densely populated parts of the Antarctic and certainly has more stations for its size than any other area of the continent. It is also visited by an increasing number of tourists.

At the time of writing the following stations were in use on the island:

Wintering stations:

·                         Artigas (Uraguay)                                (62o 11´ 04″ S, 58o 54´ 09″ W).

·                         Bellingshausen (Russia)                      (62o 12´ S, 58o 58´ W, 16 m AMSL). Bellingshausen Station is situated on the Fildes Peninsula in the southwestern part of the island. The station buildings are built on ice–free soil on both banks of a brook rising from the small Kiteg lake and flowing into the Ardly Bay. This bay is suitable for ship visits, with the disembarkation being executed with the help of boats and sometimes by helicopters. Bellingshausen Station was opened in February 1968 with the staff during the winter season consisting of about 20 people. The station is used as a base for field party investigations on King George island.

·                         Commandante Ferraz (Brazil)            (62o 05´ 00″ S, 58o 23´ 28″ W).

·                         Great Wall (China)                              (62o 13´ S, 58o 58´ W, 10 m AMSL).

·                         Jubany (Argentina)                             (62o 14´ 16″ S, 58o 39´ 52″ W, 11 m AMSL).

·                         King Sejong (Korea), Barton Peninsula,

                                                                            (62° 13´ 24″ S, 58° 47´ 21″ W, 10 m AMSL).

·                         Henryk Arctowski (Poland)                 (62o 09´ 34″ S, 58o 28´ 15″ W).

·                         Presidente Eduardo Frei Montalva (Chile), Fildes Bay.

                                                                               (62° 18´ 48″ S, 58° 55´ 30″ W, 10 m AMSL).

     (Note: Teniente Rodolfo Marsh is the 1,292 m runway next to Frei Station

     (see Figure 7.3.2.2.1).

Summer–only stations:

·                         Ardley (Chile), Fildes Bay                   (62° 12´ 24″ S, 58° 53´ 48″ W);

·                         Macchu Picchu (Peru)             (62° 05´ 30″ S, 58° 28´ 16 W, 10 m AMSL);

·                          Juan Carlos I (Spain)              (62° 39´ 46″ S, 60° 23´ 20″ W).

Figure 7.3.2.1.1     A map of King George Island.

There are also a number of huts occupied on a short–term basis in order to conduct biological research. The many operational and research activities on the island require accurate weather forecasts, particularly for the use of aircraft from Marsh. In addition, forecasts are required for the large number of ships that visit the stations for re–supply.

Figure 7.3.2.2.1     A map of the Marsh runway.

7.3.2.5                          Data sources and services provided

In this section we consider the meteorological observing programmes and forecasting activities that take place at each of the stations:

·                         Ardley. This is a summer camp at which scientific work is undertaken but not of a meteorological nature.

·                         Artigas. The Uruguayan air operations make use of the airstrip at Marsh. There is a helipad at Artigas Station. Eight surface meteorological observations are made each day and sent to Frei Station.

·                         Bellingshausen. During the 1980s weather forecasts and ice situation information were provided for Russian marine activities for the south–western part of the Atlantic and for the south–eastern Pacific. Surface observations are available via the GTS four times a day. During summer radiosonde ascents are made at 00 UTC and provided via the GTS.

·                         Commandante Ferraz. Surface meteorological observations are collected.

·                         Great Wall. Surface observations are available via the GTS four times a day. Weather forecasts are prepared on site for the station and its vicinity, and for the Chinese research ships Polar and Snowdragon. The weather forecasts are prepared using information from the Antarctic Meteorological Centres, e.g., the Frei Meteorological Centre of Chile, and from Southern Hemisphere surface, upper–air and NWP products issued by the World Meteorological Centre, Melbourne, Australia. Other data include high–resolution imagery from polar orbiting weather satellites and analysis of station elements. Meteorological information for the operation of the research vessels is processes by ship–board meteorologists with the aid of facsimile synoptic charts, satellite data, marine and meteorological observations, and weather related ship routing suggestions sent from Beijing for consideration.

·                         Jubany. Surface observations are available via the GTS four times a day. Forecasts are obtained from Marambio.

·                         King Sejong. Surface observations are available via the GTS four times a day.

·                         Henryk Arctowski. No specific information has been obtained.

·                         Presidente Eduardo Frei Montalva. Nearby there is a small village named “Villa Las Estrellas” (The Stars Village) where 15 families winter over. This makes Eduardo Frei the second largest Antarctic station after McMurdo. The following gives an overview of this major Antarctic centre:

–The Antarctic Meteorological Centre at President Eduardo Frei Montalva was established as one of the three meteorological collecting centres on the Antarctic continent. This was in accord with the resolution of the First Meeting of the Working Group on Antarctic Meteorology of the Executive Council of the World Meteorological Organization held in Australia in 1966. The "Eduardo Frei" AMC technically reports to the Dirección Meteorológica de Chile (DMC) (the Chilean Bureau of Meteorology). It functions year–round with a team of meteorologists and observers who undertake national (Chile) and international meteorological requirements regarding Antarctic activities.

–The AMC is actually located at the nearby Teniente Rodolfo Marsh airstrip (Figure 7.3.2.2.1) and has the responsibility of providing weather forecast to aviation and marine operations and to all other human activities carried out in the region such as research parties, tourism, etc. To accomplish these tasks, the AMC is staffed by three meteorologists and three observers year–round.

–The AMC also carries out the function of communication centre for the collection and world–wide GTS transmission of meteorological observations from the surrounding Antarctic stations.

–Surface, 500–hPa height and 1000–500–hPa thickness charts are available to the forecasters every 12 h.

–The AMC Eduardo Frei is in communication with the DMC via a satellite link. Numerical weather forecasts from the National Centers for Environmental Prediction are received from Washington through Santiago. A satellite receiver (HRPT) workstation with TeraScan software is installed at the AMC to obtain in situ satellite imagery at high resolution from the NOAA polar orbiting spacecraft. Radio VHF allows exchange of weather information among Chilean stations and others located in King George Island and surroundings places.

–Routine weather observations are sent internationally every three hours through the GTS via Santiago. Routine forecast products prepare by the AMC meteorologists are broadcast on HF and distributed via the GTS to all interested users. These products include ROFOR (regional forecast for aviation), MAFOR (forecast for shipping in the Southern Ocean between 20º W and 90º W, the Drake Passage and the Bellingshausen Sea) and forecast for the general public. In addition, the AMC broadcasts the IAC (coded sea–level pressure analysis), ice report, the current and predicted (24 hrs) sea level pressure chart and predicted 500–hPa heights.

–The high variability of the atmospheric conditions over the Antarctic Peninsula and in particular on King George Island implies that the weather changes from one state to another very rapidly. Thus, forecasting for the area requires a continual evaluation of the meteorological variables and of the development of the synoptic and mesoscale perturbations in the region. Frei Station has all the facilities and human resources for providing the meteorological needs for King George Island and surrounding areas. Moreover at Punta Arenas, the southernmost large city of Chile, there is a Meteorological Regional Centre that can support this effort with weather and forecast information to any aircraft and ship that goes to the Antarctic region.

·                         Macchu Picchu. No specific information has been obtained.

·                         Juan Carlos I. No specific information has been obtained.

7.3.2.6                          Important weather phenomena and forecasting techniques used at the location

General overview

The island is located in one of the most northerly parts of the Antarctic and has a relatively mild, maritime climate. It is also located at the latitude of the circumpolar trough and is affected my many active depressions that pass through the Drake Passage, bringing frequent gales and precipitation. The weather can generally be described as unsettled and gloomy weather with low stratus and strato–cumulus prevails. Precipitation is frequent and in the form of snow, rain, or drizzle. Around 817 mm of precipitation falls in a typical year at Bellingshausen. Cyclonic eddies move into this area on both zonal and meridional trajectories. The zonal systems are frequently fast–moving from west to east with speeds exceeding 28 m s–1 (~55 kt). Those arriving on a meridional trajectory from the mid–latitude area of the Pacific tend to fill over the Bellingshausen Sea. Not all the cyclones with a zonal trajectory move over the Drake Passage. Some lows track further north or south and encounter the orographic barriers of South America or the Antarctic Peninsula. Depending on the location of the lows, the wind across the island can be either from the west or the east, with cloud lingering on the upwind side of the island.

As the Marsh runway facility is of key importance it is of interest to gain an overview of the weather that Frei Station/Marsh experience. Visibility, reduced by fog and precipitation, and low cloud, are the main meteorological parameters that restrict aircraft operation in Frei Station and surrounding areas. These conditions are usually associated with stable conditions. Frontal systems coming from the northwest bring warmer and moister air toward the island stabilizing the lower atmosphere. In these cases northerly winds prevail and low stratiform cloud and fog can form. Liquid precipitation events are often associated with these northwesterly fronts. In this type of meteorological situation restricted conditions can last for more that 12 hr. On the other hand, cold air masses coming from the southwest bring unstable conditions, cumulus type clouds and blizzards. Under this latter meteorological environment the runway at Frei Base can be temporarily closed for operations. Other restrictions on operations are associated with strong winds across the runway that affect aircraft performance. One synoptic–scale situation that can produce cross–winds involves a high–pressure system being centred over the Weddell Sea. In this case a southerly low–level jet (barrier wind) can develop along the east side of the mountains of the Peninsula and extend over the northern tip of the Peninsula reaching King George Island with southerly winds. Wind shear near the surface can occur with this situation

Surface wind and the pressure field

With climatological low pressure over the Amundsen/Bellingshausen Sea the prevailing wind direction at King George Island is from the west to northwest quadrant. However, the high frequency of major depressions passing close to the area means that the winds are rather variable on a day–to–day basis and gales are frequent – for example, Great Wall reports 36% of days with winds of more than 17 m s–1(~33 kt) and a peak in gales during the months of March to October (Table 7.3.2.4.1 (in Appendix 2)). And for Frei Table 7.3.2.4.2 (in Appendix 2) shows the monthly distribution (%) of the wind velocity for given directions while Figure 7.3.2.4.1 (in Appendix 2) displays the percentage of occurrence of wind higher than certain values. Clearly, from this figure the semi–annual oscillation of the wind speed at Frei can be seen for wind speeds higher than about 8 m s–1 (~ 15 kt) – two maxima may be seen, one in April and one in October. This behaviour is not observed for wind speeds at Frei of less than 8 m s–1 – these have a maximum during the summer. In general at Frei the wind speed increases during the equinox and is, on average, higher in winter than in summer.

Anticyclones and ridges tend to be quite short–lived in the area, so that calm conditions are only reported on 1–2% of occasions, although Jubany with its sheltered location has calm in over 4% of its reports.

The local orography affects the wind as reported from the various stations and there are substantial differences in their climatological wind statistics. The group of stations on the low southwestern tip of the island tend to be more representative of the broad–scale synoptic environment, although even here there are differences between stations. Bellingshausen has most winds between west and north with some from the southeast. Frei has the same general picture (see Figure 7.3.2.4.2. (in Appendix 2)).

Great Wall on the other hand has most winds from the north and northwest (see Table 7.3.2.4.1 (in Appendix 2)). King Sejong with its location on the Barton Peninsula is exposed to the northwesterly winds, but is sheltered from southeasterlies. The winds from Jubany should be used with great care as the station is located in an enclosed fiord and most winds come from the southwest with a secondary maximum in the northeast. They are therefore not representative of synoptic conditions.

Usually north–westerly winds bring warm, moist air to the area ahead of cyclones, with south–easterly and easterly winds, often to the west of cyclone centres, bringing cold dry air. The wind direction and speed are very variable on King George Island. Sudden wind gusts are typical.

The most persistent strong cyclonic winds occur when lows arrive from the eastern part of the Pacific Ocean along meridional trajectories. At Bellingshausen Station the number of days with wind speed exceeding 15 m s–1 (~30 kt) is 10–15 per month on average, the maximum being during the winter months. On the island, strong winds often cannot be explained by the pressure field alone, because there are local factors playing a role that result in changes to the pressure gradients. In some cases these effects can be explained by the presence of mesoscale disturbances.

The major NWP models are now quite successful at analysing and predicting the locations and depths of large–scale depressions, and around King George Island the analyses can be used with a fair degree of confidence because of the large number of in situ observations and extensive satellite data over the ice–free ocean. However, satellite imagery should also be used in conjunction with the model fields because of the large number of mesoscale weather systems that are found in this area.

Upper wind, temperature and humidity

The Russian Bellingshausen Station had a radiosonde programme for many years, but ascents stopped in 1999. So today there is no upper–air measurements taken on a routine basis anywhere on the Antarctic Peninsula. Upper–air information is therefore obtained from the NWP analyses. Mean January and July upper–level wind roses for Bellingshausen 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 A3–2 (a) and (b).

Clouds

Much of the cloud that affects King George Island is frontal in origin, although some non–frontal cloud is also present. Satellite imagery allows the cloud extent and type to be assessed routinely.

When frontal systems pass the Fildes Peninsula the cloud does not change significantly, and hills are often under the cloud base if their height does not exceed 100 m above sea level. At Bellingshausen Station the mean annual cloud cover is 7.2 oktas and the seasonal and month–to–month variations are very small and do not exceed 1 okta. Conditions at Great Wall are similar (see Table 7.3.2.4.1 (in Appendix 2)). Similarly, Figure 7.3.2.4.3 (in Appendix 2) indicates that more than 70% of the time the cloud at Frei is 6 oktas or more. On about 7% of occasions at Frei cloud heights of less than 150 m combine with visibilities of less than 1500 m and thus severely restrict aviation operations.

Cloud can be predicted in the short term using satellite imagery. For longer–range forecasts the cloud must be estimated from the broad–scale synoptic environment that is expected.

Visibility: snow and fog

Visibility can be reduced considerably by the moderate or heavy snow that falls in association with the frontal cyclones. Good visibility (greater than 10 km) is recorded on more than 90% of all occasions and the frequency of low visibility (less than 2 km) is 2–6% of days per month. During the winter months poor visibility usually occurs as a result of the frequent snow–storms (up to 10–12 days), and during the summer months fog as well as precipitation (up to 8–10 days) is among main reasons for the reduction of visibility.

The probability of fog increases with the passage of a warm front with northerly winds and under such conditions the fog can occur ever in the presence of strong winds. Snowstorms occur with fresh snow cover and at wind speeds exceeding 7–9 m s–1 (~15 kt). The probability of a snow–storm increases under dry snow conditions.

An analysis of the seasonal occurrence of visibility less than 1600 m for various wind directions has been carried out for Frei Station and Figure 7.3.2.4.4 (in Appendix 2) summarises the results. Comparing this figure with Figure 7.3.2.4.2 indicates that at Frei visibility reductions below 1,600 m occur with all wind directions. Figure 7.3.2.4.5 (in Appendix 2) shows the percentage frequency of several visibility thresholds at Frei for each season. It may be seen that between 20 and 30% of the time visibility at Frei is less than 1,600 m with a maximum during summer and a slight minimum in autumn.

Surface contrast including white–out

With the large amount of low cloud and frequent precipitation events experienced at King George Island surface contrast can be very poor. It is forecast using an estimate of the likelihood of cloud and the occurrence of precipitation.

Horizontal definition

Horizontal definition is generally moderate or good because of the large amount of open water that is found around the island and the orographic features that are visible.

Precipitation

On King George Island precipitation falls on 70% of days over the year, but with a minimum during the summer months (see Table 7.3.2.4.1 (in Appendix 2)). The precipitation is usually associated with the many frontal depressions that occur in this zone. Solid precipitation (snow, snow grains, pellets of snow) prevails during the year, but liquid and combined precipitation are found not only in summer, but also in winter. Figure 7.3.2.4.6 (in Appendix 2) shows the number of days per month when liquid and solid precipitation occur at Frei while Figure 7.3.2.4.7 (in Appendix 2) shows monthly precipitation amounts at Frei. The effect of semi–annual oscillation is quite evident in both these figures.

Also of interest is the intensity of precipitation. Figure 7.3.2.4.8 (in Appendix 2) gives an indication of precipitation rates at Frei for 24 hr periods. It may be seen from this figure that around 27% of precipitation events at Frei have 24 h rates in the range of 6 to 8.9 mm for the 24 h. Intense rainfall rates of, say, greater than 21 mm per 24 h period occur on less than 5% of occasions.

Precipitation can be forecast directly using the model output or if model precipitation fields are not available then the surface pressure fields.

Temperature and chill factor

The maritime climate of King George Island means that the annual cycle of temperatures is less extreme than at many other sites in Antarctica and at Arctowski Station over 1978–87 the mean daily temperatures varied from 2.3oC in January to –7.1oC in July. During this period the coldest temperature recorded was –32.3oC and the highest 16.7oC.

A similar range of mean temperatures occurs at Great Wall (see Table 7.3.2.4.1 (in Appendix 2)) and at Frei. The monthly average of the mean temperature at Frei Station is depicted in Figure 7.3.2.4.9 (in Appendix 2). Positive values occur in summer (December, January and February) and near zero degrees in March. A minimum takes place in July of about – 6°C. The inter–annual variability, given by the standard deviations of mean–monthly temperatures shown in Figure 7.3.2.4.9, has a winter maximum. Figure 7.3.2.4.10(in Appendix 2) shows the monthly distribution of temperature at Frei for occasions when the temperature is above 0ºC. As expected, the frequency decreases toward the winter months where only 5% of the recorded three–hourly temperatures were above freezing. In contrast, more than 70% of the temperatures are about 0°C in summer, with a maximum in January. In the range between –10°C < T° < 0°C (see Figure 7.3.2.4.11 (in Appendix 2)), the frequency is higher in May and October, decreasing significantly toward the summer with a minimum in January of less than 10% in mid–afternoon, and another relative minimum in July of about 55%. Occasions (not shown) when the temperature is below –10°C reveal a maximum frequency in winter with about 40% in July during the night hours.

Temperature changes can be predicted using model fields or through the use of satellite imagery to estimate the likelihood of changes of air mass.

Icing

Icing can occur on King George Island because of the rapid variations in temperature that are experienced coupled with the availability of large amounts of cloud liquid water. Icing events at Bellingshausen Station can occur on 8–12 days per month during the period from May to September.

Turbulence

No specific information on forecasting has been obtained.

Hydraulic jumps

Hydraulic jumps have not been reported on King George Island.

Sea ice

At Bellingshausen Station regular ice observations have been carried out in Maxwell Bay, including Ardly Bay and in the visible parts of the Bransfield Strait and the Drake Passage. The most reliable and complete data about the ice situation is available for Ardly bay due to the good visibility there. The results of observations, carried out since 1968 demonstrate that the ice conditions in this bay are characterized by large inter–annual variations. So, the maximum thickness of fast ice varies from 50 to 124 cm, and the number of days with stable ice (from the moment of stable ice formation to the full clearing of the ice) is from 82 to 220.

Passive microwave, visible or infra–red satellite imagery can be used to estimate the broader scale extent of the sea ice. Short period variations in sea ice position can be estimated from the forecast surface winds.

Wind waves and swell

No specific information on forecasting has been obtained.