7.9                                   Queen Mary Land  

Queen Mary Land extends between meridians 91º E to 102º E (see Figure 7.9.1). From west to east, key features or stations/bases referred to in this section include:

·                         The Davis Sea;

·                         Mirny Station                                       (66º 33' S, 93º 01' E, 35 m AMSL);

·                         The Shackleton Ice Shelf;

·                         Edgeworth–David Base                      (66º 15' S, 100º 36' E, 6 m AMSL);

·                         "Oasis"/Dobrowolsky                          (66º 16' S, 100º 45' E, 28 m AMSL;

·                         Bunger Hills.

7.9.1                                Mirny Station

7.9.1.1                          Orography and the local environment

Mirny (opened on February 15, 1956) is situated on the coast of Cape Davis at a small protrusion of Mirny Peninsula at 66º 33´ S, 93º 01´ E and elevation of 35 m AMSL (see Figure 7.9.1). The shore in the vicinity of the station is called Pravda shore. The station structures are located at four rock outcrops. The mainland shore presents a snow–ice barrier of about 15–20 m above sea level. The ice surface south of the station rises to a height of 1.5 km at a distance of 100 km. A 10 m isobath passes in 15–20 m from the coastline. Offshore there is a group of rocky islands known as the Haswell Islands. Land–fast ice near the station is observed much of the year reaching 30–40 km in width by the end of the winter.

7.9.1.2                          Operational requirements

Mirny is the main base of Russian studies in the Antarctic. One of the main functions of the station is to provide support for activities at Vostok Station. For the last few years, the supplies were delivered to Vostok from Mirny by surface–transport vehicles. A permanent synoptic group at the station provides forecasts for transportation traverses along the Mirny–Vostok–Mirny route, cargo operations near the land–fast ice and at the approaches during the navigation period, as well as for other operations.

7.9.1.3                          Data sources and services provided

Information received in the form of synoptic messages, ship–borne observation and drifting buoy data allows a synoptic group to compile weather and air pressure orography charts for 00 UTC for the coastal areas, the Cosmonauts, Sodruzhestvo and Davis Seas. Up to five IR or visible images from meteorological satellites are received on a daily basis. A restricted portion of upper–air–synoptic information from the European Centre for Medium–Range Weather Forecasting for the Southern Hemisphere is received via INMARSAT in GRID code. Synoptic information is also received from the Melbourne Regional Meteorological Centre via HF facsimile. Based on this information, weather forecasts are provided for marine, ground, and air operations.

7.9.1.4                          Important weather phenomena and forecasting techniques

General overview

The station is located in the climatic area at the ice slope foot. The weather character is governed by frequent blizzards especially in winter and by strong katabatic winds. The yearly air temperature average is –11.3ºC with a maximum temperature of +6.8ºC and a minimum of –40.3ºC. The average wind speed is 11.2 m s^–1 (~ 22 kt) with a maximum of 56 m s^–1 (~ 109 kt). East–southeasterly winds predominate. During the year, there are 204 days on average with the wind speed in the station area greater than 15 m s^–1 (~ 29 kt).

The polar day lasts about a month (from December 10 to January 10), the polar night is almost absent. Cyclonic activity is the prevailing component of the circulation climate–forming factor for the study area. The influence of the Antarctic high on climate is less significant here and is explicitly manifested in the absence of cyclonic depressions near the Pravda Shore. High–pressure ridges can form connecting the Antarctic High with the subtropical High. In these cases, the maximum atmospheric pressure values are recorded at the coastal stations.

The cyclonic eddies forming the weather at Mirny Station move to this region both along zonal and meridional trajectories. Weak lows of the Antarctic front moving along the coast rarely result in significant weather deterioration in the vicinity of Mirny. Active polar frontal depressions from temperate oceanic latitudes are mainly generated in the areas of cyclogenesis near South Africa and between Crozet and Kerguelen Islands. These depressions are blocked by the high Antarctic continent from the south and longitudinal ridges from the east allowing repeated regeneration of deep depressions that persist near the coast. A high frequency of mobile active cyclonic eddies is typical of the cold season, such processes being less frequent in summer. The especially dangerous weather phenomena for the station activities are caused by active lows.

Surface wind and atmospheric pressure field

Mean–monthly values of wind speed at Mirny are given in Table 7.9.1.4.1 (in Appendix 2). Three main winds are identified in the Mirny Station area:

·                         The cyclonic winds connected with cyclones moving over the Pravda Shore have northeast–east or east–south–west directions. They are quite stable in speed and direction and their speed increases with height. The characteristics of these winds that are typically accompanied with snowfall and warming are determined by the direction of motion and evolution of the cyclonic eddies. Meridional movement of lows, particularly when they persist near the coast due to blocking, cause the cyclonic winds to be more persistent and stable than with zonally mobile depressions.

·                         The katabatic winds depend on a number of factors (slope and coastal orography, thermal conditions, gravitation and gradient wind) are accompanied by below zero temperatures, high air dryness and predominantly clear weather. In summer and during the transient seasons with diurnal temperature variations, the katabatic flows arise or intensify in the evening reaching their maximum around 5–8 hr local time attenuating by 15–18 hr and then increasing again. In the wintertime the katabatic wind speeds increase and their attenuation or increase depend on the change of the pressure gradient with approaching cyclones. The katabatic wind in the coastal area completely decreases at a distance of 10–15 km from the foot of the slope and here the influence of the pressure systems is manifested to a full extent.

·                         Transient winds that have simultaneously the characteristics of the katabatic and cyclonic winds have an east–southeast direction and strongly depend (as do the cyclonic winds) on the direction of motion and evolution of the cyclonic eddies.

Each of these three wind types is characterized by specific weather conditions and by changes in the profile and the temperature with height. Forecasters have to take into account the vector directions of the katabatic flow and the pressure gradient wind. The wind will be weaker if these components oppose each other and will be stronger if they coincide. In reality, it means that the wind in the sink zone may attenuate with cyclones approaching from the west. The highest wind speeds are observed to the rear of cyclones with the coincident vectors of the katabatic and synoptic pressure gradient winds.

The maximum number of days in a year when storm force winds were recorded at Mirny was 247. Storm–force winds are strictly from a southeasterly direction that is highly constant. The average speeds of storm force winds with the passage of cyclones are higher than those due solely to katabatic influences. Around 20–25 days with hurricane force winds occur per year. The maximum wind speed of 56 m s^–1 (~ 109 kt) recorded at the station, was an easterly cyclonic wind. The maximum frequency of occurrence of storm and hurricane force winds occurs in winter.

Storms may last from several hours to several weeks. A case was recorded in Mirny where the katabatic storm wind persisted continuously for 220 h. Calm weather and weak winds comprise only about 3% of all cases observed.

A semi–annual component in the seasonal variability of the atmospheric pressure at sea level is typical of Mirny Station with the amplitudes of the semi–annual oscillations greater than those of the annual oscillations. The maximum of the semi–annual wave is observed in winter with the minimum in the transient seasons. Mean–monthly values of station–level pressure and MSLP at Mirny are given in Tables 7.9.1.4.2 and 7.9.1.4.3 (in Appendix 2).

Clouds and precipitation

The amount of total cloud in the Mirny area is 5.1 oktas, on average throughout the year. The frequency of occurrence of low cloud producing precipitation is insignificant, being 10–15%.

Active cyclonic activity in the Antarctic coastal zone contributes to the development of all cloud forms, excluding strong cumulus clouds. Cloud–free sky is frequently observed under the effect of the Antarctic high especially in winter.

	Figure 7.9.1     A map showing locations in Queen Mary, Wilkes, Terre Adélie and George V Lands and adjacent areas. (Adapted from a map provided courtesy of the Australian Antarctic Division.)

Typically in summer, high and middle clouds prevail. Low stratocumulus clouds 600–1000 m (~2000–3300 ft) high move to the coast from the sea. Cloud height below 300 m (~1000 ft) is rare. However, with deep cyclones moving over the Pravda Shore along meridional trajectories at any time of the year, strong advection of warm and moist air occurs from the north in the frontal zone. The passage of the fronts is accompanied by continuous low cumulus. In such situations, the snowfall can last continuously for 5–7 days.

Corresponding to cyclonic activity, the maximum precipitation at Mirny is observed in wintertime and the minimum in December and January. Around 400 mm of precipitation falls over the year, the number of days with precipitation being 146. Precipitation is mainly solid except for infrequent cases in the summer months.

The quality of cloud forecasting and correspondingly, precipitation forecasting, depends on the availability of frequent satellite information. Cloud forecasting can be based in general on the dependence revealed for the Mirny area between clear or overcast sky and the wind direction in the troposphere. The largest number of days with clear weather during a year is related to southwesterly and southeasterly winds. The southwesterlies are associated with the southeastern periphery of a ridge or sub–polar high while the southeasterlies are governed by the influence of the rear part of the southern half of lows. Typically, katabatic wind is observed at the station under such conditions.

Gloomy weather, often with snowfall, is predominantly connected with northeasterly and northwesterly winds, which characterize the cyclonic circulation in the vicinity of Mirny. In summary, clear weather dominates with offshore air–flow and gloomy weather with onshore air–flow.

Visibility: blowing snow and fog

High transparency and an almost absolute air purity, which provide good visibility conditions, are typical of Antarctica. However, the Mirny area is characterized by weather phenomena that significantly deteriorate visibility. A reduced visibility forecast is primarily connected here with forecasting strong wind and snowfall.

Blizzards significantly reducing the visibility are frequent due to active cyclones moving towards the coast along a meridional trajectory. The strongest blizzards are observed in the cold half of the year and in the rear sector of passing cyclones where the wind speeds may be greater than 50 m s^–1 (~100 kt). Blizzards in combination with low air temperatures create extremely severe weather conditions. In the summer months, however, three to four cases of persistent (up to three days) strong blizzards are also possible with visibility reduced to 50 m or less and wind speed up to 30 m s^–1 (~60 kt).

The success of predicting blizzards depends on the capability of correctly defining development and duration of depressions with which the occurrence of this phenomenon is connected. The duration of blizzards in rapidly–moving cyclones is short comprising around half a day. The onset of a blizzard is determined by the visibility reduced to several tens of metres. This typically takes place during a heavy snowfall in a northerly wind of more than 10 m s^–1 (~19 kt) and during a less heavy snowfall in a southerly wind of more than 13 m s^–1 (~25 kt). Obviously, the end of a blizzard is to be expected as the wind decreases below the criteria indicated.

Snowstorm events that decrease visibility (without snowfall) are also predicted from the wind increasing to 10–13 m s^–1 (~20–25 kt). In predicting a snowstorm event the cases with a pressure gradient and a katabatic wind should be differentiated. The katabatic winds do not spread more than 10–15 km from the coast notwithstanding their intensity in the station area. Snowstorm events due to the pressure gradient wind can be observed over the entire area. In late spring and up to late summer, approximately from November to February, snowstorms are rare at the coast and on the continent near the coast during wind increases due to the changed snow surface structure under the influence of direct solar radiation. Their occurrence is predicted only in the presence of freshly fallen snow.

The highest frequency of occurrence of snowstorms is observed in winter up to 26 days with snowstorm per month and in summer up to 10 days per month. The overall duration of snowstorm events in Mirny averages 3.5 months throughout a year.

Advective maritime fog at Mirny is observed once in two years, on average, in summer. Such event arise typically with weak northerly or westerly winds and do not seriously hamper the operation of ground transport vehicles and aviation due to their short duration and insignificant spreading inland.

In the case of such fogs, landing of light aircraft is possible at the dome. Fogs of this type are not typically included in forecasts due to their exceptionally low frequency of occurrence and correspondingly due to the lack of experience of their prediction.

Frost or ice fogs and haze resulting from the process of sublimation and condensation of atmospheric moisture in the form of ice crystals or rime, are also extremely rare in the Mirny area. They are however, common for the inland areas where they hamper the operation of ground vehicles. Forecasting of these phenomena should be based on the favourable conditions for accumulation of ice crystals in the surface layer, which occurs in calm weather in the central parts of highs or ridges when clear weather or thin cirrus clouds are observed. The maximum frequency of occurrence of frost or ice haze and fog is observed in winter and the minimum in summer.

The phenomenon of snow haze at wind speeds of 3–5 m s^–1 (~6–10 kt) can be observed in Mirny and more frequently over the inland regions. It is caused by fine snow dust in the suspended state after snowstorms. This phenomenon is mainly typical of the cold season if there is reduced density of snow cover. The visibility is not greatly affected being 6–4 km. A snow haze forecast can be issued as a forecast of the phenomenon following drifting snow when wind is expected to decrease to 5–3 m s^–1 (~6 to 10 kt).

The frequency of occurrence of good visibility (10 km and more) in the Mirny area in summer is around 80% decreasing to 50–60% in the winter months.

White–out

The optical phenomenon ‘white–out’ can be observed both in the vicinity of the station and at the ice dome. Forecasting should take into account that ‘white–out’ occurs more often near midday (due to higher sun elevations) in the frontal part of deep depressions with dispersed upper fronts.

Temperature and chill factor

Mean–monthly values of temperature at Mirny are given in Table 7.9.1.4.4 (in Appendix 2). The Mirny area is characterized by below zero monthly temperature averages throughout the year and the absence of a pronounced winter minimum. The maximum monthly temperature average is observed in January. The absolute maximum recorded over 25 observation years was +6.8ºC. Significant air temperature oscillations from day–to–day during a year are always connected with deep lows passing the coast from the northern oceanic regions. The temperature increase at the station is typically observed at the east wind change. The success of air temperature forecasts is determined by forecasting the motion and evolution of cyclonic features. The temperature anomalies within a year have positive values with meridional circulation and negative values with zonal flow.

Low air temperatures and wind speed are the major factors restricting outdoor activities. A combined effect of these factors governs the intensity of chilling of that part of the human body that is unprotected by clothing. Experimental studies, using special instruments, were performed over one year in Mirny to determine the intensity of cooling. The results have shown that on 48% of occasions the weather was suitable for work in the open air; on 49% of occasions there was a risk of frostbite; and only on 3% of the time (10 days) the weather was so severe that even a short stay in the open without special face protection was impossible.

Icing

Ice deposition on objects in the form of rime and glaze at Mirny is quite rare. The total duration of rime phenomenon is about three days, on average for a year. Glaze forms predominantly at air temperature between 0 to –3ºC being found for 20–30 hr a month from November to January and for several hours and less than an hour in the other months.

Sea ice

First indications of ice formation in the Davis Sea appear in early March, however, due to strong autumn winds stable ice formation does not begin until the second 10–day period of March, on average. The duration of the onset of stable ice formation before the establishment of land–fast ice comprises about a month for the Mirny area. Land–fast ice is established at ice thicknesses of about 20–40 cm. Land–fast ice thickness reaches its maximum values in the second 10–day period of November at the end of the ice growth. The maximum land–fast ice width in the Davis Sea in September–October reaches 30–40 km. The dates of land–fast ice break–up in the vicinity of Mirny vary between January 27 and March 9 (with February 13 as an average date). East of Mirny a significant concentration of icebergs forms resulting from a slower drift of icebergs produced by the outlet Helen Glacier. Similar aggregations of icebergs in the central and northwestern Davis Sea are due to shallow water depths resulting in their grounding.

Wind waves and swell

No information on forecasting was obtained.

7.9.2                                Edgeworth David Base (Bunger Hills)  

7.9.2.1                          Orography and the local environment

Edgeworth David is a campsite located on the southwestern perimeter of the Bunger Hills, adjacent to Transkriptsii Gulf, adjoining the glacial ice sheets extending into the Shackleton Ice Shelf (see Figure 7.9.1 and Figure 7.9.2.1.1).

The Bunger Hills are on the Antarctic coast, about 75 km (~40 nm) inshore of Mill Island and the attached Shackleton Ice Shelf at an approximate location of 66º S, 101º E. The Bunger Hills cover an approximate area of 37 km by 28 km (~20 nm by 15 nm), with the long axis abutting the continental ice sheet to the southeast. Moraine and glacial rubble cover most of the exposed rock, which is otherwise bare or sparingly covered in snow. The area is made up of islands and isthmuses dotted with freshwater cairns. Much of the area is near sea level with frequent steep sided hills rising less than 150 m (~500 ft). Edgeworth David’s site on the western flank of the hills provides significant shelter from the prevailing east to southeasterly winds.

7.9.2.2                          Operational requirements and activities relevant to the forecasting process

Edgeworth David was used as a summer camp supported by ship and helicopters operations in the summer of 1985/86. A coastal depot was established on the Shackleton Ice Shelf to the west of Mill Island, from where helicopters sling loaded equipment and ferried expeditioners approximately 75 km (~40 nm) to the camp across the ice shelf. Re–supply by air remains the most probable method even now, due to the heavy and frequent crevasses evident in the ice shelf.

In the summer of 1985–86 Edgeworth David supported the operation of two Hughes 500s and one Bell Jet Ranger helicopter. Equipment and fuel dumped at the coast was ferried to camp when over–ice flying operations were possible. Otherwise, the aircraft were used to deploy and recover field parties within the Bunger Hills, and for expeditionary investigations to the west, which encompassed the Obruchev Hills, the Denman Glacier and surrounding mountains and coast. The Jet Ranger was also used for aerial photography.

Aviation forecasts were required each day for the helicopters as necessary. These forecasts would frequently dictate aircraft activity for the day, dependant principally upon the extent of white–out.

Under the emergency evacuation plan, the helicopters would hop to either Mirny or Casey utilizing fuel dumps at coastal midway points to either location. A route forecast would be required to help select the appropriate destination. Future operations may seek to use the permanently frozen Transkriptsii Gulf for fixed wing operations. The multi–year ice is about two metres thick and only shows weakness at the edges where tide cracks follow the contour of the shore.

7.9.2.3                          Data sources and services provided

A forecaster at Edgeworth David is dependent upon equipment ferried in from the coast, which must be able to run on intermittent generator power.  This would normally produce APT satellite reception, HF chart reception, scheduled data broadcasts from Casey Station and local data, including pilot balloons, barograph and screen based observations.

7.9.2.4                          Important weather phenomena and forecasting techniques used at the location

General overview

Table 7.9.2.4.1 (in Appendix 2) is a summary of the means of a few of the elements observed during the 1986 summer at Edgeworth David (Nairn, 1986), while Table 7.9.2.4.2 (in Appendix 2) is a similar summary of data observed at the nearby Oasis base in the 1958 summer. In general, during the operation of the summer camp in 1985/86 marginal conditions were mainly encountered in the prevailing easterlies. Weather patterns delivered complex and difficult forecasting problems. If weather systems moved slowly, it was not uncommon for a low or extensive frontal band to move inland, resulting in extensive penetration of moisture inland with very strong easterly winds (> 35 m s^–1 (~ 70 kt) in the low levels up to 3600 m (~ 12,000 ft)). If weather systems moved rapidly, gales could onset rapidly, with low cloud following quickly from the west.

Prevailing strong south easterly winds across the Bunger Hills frequently produced strong turbulence adjacent to the continental ice sheet, with winds grading to light at Edgeworth David. The summer camp temperature generally rose a few degrees above freezing during the day, reaching above 10ºC on a few occasions (see Table 7.9.2.4.1 (in Appendix 2)). Precipitation was infrequent and on one notable occasion fell as rain.

The Bunger Hills are frequently affected by deep slow–moving lows to the north. On average, a stable long wave trough is found at the longitude of the Shackleton Ice Shelf during summer. Consequently, lows are often rapidly advected in from the northwest, and may recurve to the west after becoming embedded in the circumpolar trough. These large synoptic scale weather systems are well handled by the models, and have resulted in multiple day gales at Edgeworth David.

Satellite imagery is an important forecasting tool for verification of numerical model predictions and short term development. Frequently, deep depressions over the Southern Ocean are made up of multiple centres, or have well defined centres of cyclonic vorticity advection (see Section 4.2.5) that explain short term increases in wind velocity. Broad scale advection of moisture into the continent to the east of the Bunger Hills must also be monitored, as easterly return flow to the coast would result in white out and possible precipitation. Visible imagery is an important tool for detection of cloud over the inland ice sheet, particularly as the similar surface temperature of cloud and ice reduces the effectiveness of infra–red imagery.

Significant mesoscale lows are rarely detected in this part of the coast due to the lack of significant orography. The area around the Denman Glacier was noted for its interesting weather phenomena. Most notable was the recurrent hydraulic jumps. This phenomenon’s scale was reported on the scale of the width of the glacier. A more broad–scale hydraulic jump may have been present as evidenced by the severe weather conditions experienced in the Bunger Hills. It was not possible to determine if broad scale hydraulic jumps were active during severe wind events due to restricted transport.

Surface wind and the pressure field

The wind direction is equally determined by the prevailing easterly pressure gradient and the broad–scale southeasterly katabatic flow generated by the interior continental ice slope across the eastern shield.

Wind speed is determined mainly by the oceanic pressure gradient and on occasions by the strength of the katabatic flow, which appears to strengthen when easterly gradients reinforce continental outflow to the southeast of the Shackleton Ice Shelf. In the event of gradient–reinforced katabatic flow, severe turbulence occurs along the coast. It is particularly evident over the hills, where a semi–permanent layer of low to mid–level cloud forms parallel to the continental ice sheet, with the cloud lowering as the turbulence increases. Mammatus and turbulent billows were observed on occasion.

During weak pressure events, winds became light and variable over the hills, although moderate south easterly flow continued diurnally along the eastern flank of the hills. This wind usually eased significantly during the morning, resuming during the night. It was during these lulls in the pressure field that conditions permitted operations extending to the Denman Glacier and the exposed coast and interior ranges at the head of this glacier.

Upper wind, temperature and humidity

These fields were taken directly from the model fields available on HF facsimile transmissions from Australia, and were augmented by local observations to 3000 m (~10,000 ft) using pilot balloon. Adjustments to the chart patterns were also made in the light of the satellite imagery.

Clouds

A semi–permanent bank of stratocumulus and sometimes altocumulus would develop over the Bunger Hills when strong south easterly winds occurred. This cloud bank was a good indicator of strong turbulence along the continental ice sheet edge.

Middle level cloud frequently resulted in white–out, particularly for flights to the coast over the unrelieved ice shelf. An unreliable aide in these events was the use of ‘water cloud’ signatures, where open sea or ice leads would show as a darkened underside of the cloud. This water cloud would assist pilots to break up some of the white out, particularly when determining the horizon. This tool was unreliable due to the frequent presence of blowing snow across the ice shelf. It is also important to remember that it was only useful with the sun behind the pilot, flying to the coast. Return flight was significantly more difficult, unless the pilot could gain significant altitude to sight the Bunger Hills.

Visibility: blowing snow and fog

Visibility across the region was generally very good due to the lack of pollution sources. White–out, however occurred regularly, as significant middle level cloud masses passed over the region in association with the frequent passage of deep lows.

Reduced visibility due to mist or fog was not reported in the hills or the coast. In the Bunger Hills the lack of significant exposed water areas and the distance from the coast guaranteed the absence of these phenomena. There may have been some events on the coast, but during this camp there were few light wind events and no reports from flight crews. Blowing snow was not a problem in the hills due to the lack of snowfall.

Mill Island was frequently obscured by drifting snow. North and west of the High Jump Archipelago the winds appeared to funnel against rising orography, increasing by 5–10 m s^–1 (~10–20 kt). This drift was often a determining no–flight factor when combined with marginal white out conditions.

Surface contrast including white–out

White–out did not affect field parties as their movement was confined to the hills. Aircraft activities were confined to the hills during white–out.

Horizontal definition

Edgeworth David camp was enclosed by hills on its eastern flank and the Edisto Glacier, across permanent sea ice on its western flank. Hills ranged from 100 m to 500 m, whilst features of the Edisto Glacier ranged approximately from 1 to 2 km. Ranges below 2 km did not offer any useful indication for visibility reduction, particularly given the lack of weather impact on the southwestern sector of the Bunger Hills.

Precipitation

Precipitation only occurs as a significant broad scale low brings warm conveyor belt moisture over the coast. In one event, where strong northerly advection occurred, rain developed. The other two events produced snow when a westward moving front brought warm sector cloud south of the low, along the coast and moving west–northwest back to the coast from the continent. Forecasts of precipitation are heavily dependent upon reliable satellite imagery interpretation.

Temperature and chill factor

Temperature ranges are modest due to the normally windy conditions. Colder conditions affected field parties more as night redeveloped and the hours of dark lengthened. The principal difference in the temperature ranges shown in Tables 7.9.2.4.1 and 7.9.2.4.2 (in Appendix 2) for Edgeworth David and Oasis camps, respectively, can be attributed to the Oasis record extending to the end of March, whereas Edgeworth David was evacuated at the start of March. The lower maximum and minimum temperatures would have posed a significant restriction upon Edgeworth David camp activities given the camp was equipped for warmer conditions.

Icing

No icing was reported during the 1985–86 summer camp.

Turbulence

Severe turbulence was frequent across the Bunger Hills and in the vicinity of the base of the continental ice slope. Some site specific turbulent characteristics of the area that have been noted are:

·                         Bunger Hills: The Edgeworth David base is extremely well protected from prevailing east and southeasterly winds. Hence observations at Edgeworth David are not representative for flight conditions elsewhere. Field parties indicated that in easterly airflows, strong winds extended within 9 km (~5 nm) of the base of the ice plateau on the northern, eastern and southern margins of the hills. For example if a pilot balloon measured easterlies at 23 m s^–1 (~45 kt) above 600 m (~2000 ft) then surface to 300m (~1000 ft) winds channelled in northeast to southwest oriented valleys were greatly strengthened and gusty. These winds would consistently average 25 m s^–1 (~50 kt) gusting greater than 35 m s^–1 (~70 kt) and pilots would report moderate to severe turbulence within 9 km (~5 nm) of the edge of plateau. It is supposed that the katabatic or gravity winds combined with gradient winds to produce the high surface winds and severe turbulence. Pilots reported blowing snow on the plateau reaching as high as the cloud base (around 900 m (~3000 ft)). In these strong easterlies, Edgeworth David was relatively warm (+4 to 7ºC), with 10 to 15 m s^–1 (~20 to 30 kt) winds, gusting to greater than 20 m s^–1 (~40 kt) by late morning or early afternoon. A guide to turbulence in these moist air streams is a semi–permanent roll cloud sitting inside the eastern margin of the hills.

·                         Denman Glacier: This glacier is west of Bunger Hills. It was noted that even in a light pressure gradient wind, strong winds would not allow helicopters to land on rock pinnacles at the base of the Glacier, while another party was able to land on the nearby Watson's Bluff in light and variable winds. Now, Watson's Bluff is elevated and the contrast in wind behaviour would seem to indicate that a shallow katabatic–drainage wind was occurring at the base of the Denman Glacier. On other occasions with easterly flow present this area was unflyable. It was generally found that drainage winds could add up to 20 m s^–1 (~40 kt) to winds recorded on pilot balloon flights, for example, the Edgeworth David pilot balloon flight at 1500 m (~5000 ft) would show 20 m s^–1 (~40 kt) easterly while the wind at 1500 m over the surface of Denman Glacier (pilot observation) was 40 m s^–1 (~80 kt) southeasterly, with very severe turbulence. Moreover, very severe turbulence was also encountered near hydraulic jump phenomena. These jumps developed very rapidly (pilot observations) with recorded aircraft vertical displacements of +/– 450 m (~1500 ft).

·                         Obruchev Hills: The steep fall of the plateau to the southeast of these hills supplies a consistent strong katabatic. In an easterly wind regime (23 m s^–1 (~45 kt) synoptic flow) southeasterly surface winds have been recorded in excess of 40 m s^–1 (~ 80 kt). Pilots have also recorded severe downdrafts to the southeast of the hills (that is, up wind). In one case even with full power a Hughes 500 helicopter could not climb.

Hydraulic jumps

Pilots frequently reported the rapid development of hydraulic jumps moving down (and confined to) the Denman Glacier. On one occasion an aircraft nearly crashed when landing to the west of a range adjoining the Denman Glacier. It appears that the stable stratified southeasterly flow developed a stable rotor in the lee of the range, reversing the easterly wind. Without visual clues to detect the new wind direction the pilot nearly stalled on landing with a tail wind

Short trails of fair weather cumulus, which can be seen in the vicinity of the base of the Denman Glacier, are also thought to indicate the presence of hydraulic jumps. Such cumulus is thought to have developed from the top of the hydraulic jump wall, where evaporation of the vertically blown snow and recondensation leave tell tale cloud. Under these circumstances this cloud will quickly disperse in the surrounding dry air, which fits with the short trail of cloud.

Sea ice

Sea ice off the Shackleton Ice Shelf forms as fast and pack ice during winter. Its break up can be unreliable due to a very large semi–permanent iceberg that grounds on a bank well off shore. During the 1985–86 camp, little pack ice was encountered until the Shackleton Ice Shelf. In the subsequent year, the ship became beset in pressure pack ice, which was packing against a very large iceberg to the west of the ship. Satellite imagery failed to find this iceberg the year before, yet the iceberg was easily found on imagery in the summer of 1986–87, and matched Russian maps that noted its location. It appears that a section of ice shelf broke away and then drifted to the same bank.

Wind waves and swell

Wind waves are computed from model surface wind speed, and fetch or duration. Swell has to be estimated using knowledge of wind and wave conditions over the previous few days and the few available swell observations. NWP model output is used where available.