7.3.6                                The West–Central Section of the Antarctic Peninsula

7.3.6.1                          Orography and the local environment

The west–central region of the Antarctic Peninsula covers the low–lying area on the west–facing side of the Antarctic Peninsula (see Figure 7.3.6 and Figure 7.2.1.1.1). The research stations are located on the many islands in the area or on the coast of the Peninsula itself. The stations covered in this section are:

·                         Akademik Vernadasky (Ukraine–formerly the UK Faraday Station) (65° 15´ S, 64° 16´ W, 7 m AMSL) is located on the Argentine Islands (Galindez Is.). The Argentine Islands are a group of small islands separated from the Antarctic Peninsula by the 7 km wide Penola Strait. The Argentine Islands are ice–capped and do not rise more then 50 m above sea level. The largest Galindez Island is about 1.5 km long by 1 km wide where station Akademik Vernadsky is situated on Marina Point at the northwestern end of the island. The station area is mainly sheltered by an ice shelf from the cold southerly winds and more exposed to northerly winds from the Pacific. There are a lot of ice–free areas, pools of open water near the station and waterfalls from the rock cliffs and ice shelf during the summer.

·                         Almirante Brown (Argentina) (64º 54´ S, 62º 52´ W, 10 m AMSL). Located at Paradise Bay on the West Antarctic Peninsula.

·                         Palmer (USA) (64° 46´ S, 64° 03´ W, 15 m AMSL). Located on Anvers Island in the Palmer Archipelago slightly outside the Antarctic Circle.

·                         Matienzo (Argentina) (64° 58´ S, 60° 04´ W, 32 m AMSL).

·                         Melchior (Argentina) (64° 20´ S, 62° 59´ W, 7 m AMSL).

·                         Yelcho (Chile) (64° 52´ S, 63° 35´ W, 10 m AMSL). Located on the southern shore of South Bay on Doumer Island, Palmer Archipelago.

·                         Presidente Gabriel Gonzalez Vidiez Station (Chile) (64° 49´ 12″ S, 62° 51´ 48″) is located on the western side of the Antarctic Peninsula.

7.3.6.2                          Operational requirements and activities relevant to the forecasting process

The requirements/activities at the various stations are:

·                         Vernadasky is a year–round station. The Ukrainian Antarctic Center maintains year–round scientific research programmes at the station Akademik Vernadsky, where the longest series of meteorological observations (since 1947) in the Antarctic Peninsula region have been carried out. Forecasts are required for station activities and boating operations.

·                         Almirante Brown is a summer–only station.

·                         Palmer is an all–year station. A wide range of research activities takes place on the station, including meteorology and life sciences. There is an unprepared snow skiway at the station (see Figure 7.3.6.2.1) that runs almost due east–west, with the western end at 101 m AMSL and the eastern end 128 m AMSL. The strip is often unusable from the end of December to March due to melt. A map of the airstrip is shown in Figure 7.3.6.2.1. There are no forecasters located at Palmer.

·                         Matienzo is a summer–only base.

·                         Melchior is a summer–only base.

·                         Yelcho is a summer–only refuge.

·                         Presidente Gabriel Gonzalez Vidiez is a summer–only station.

7.3.6.3                          Data sources and services provided

·                         Vernadasky. There are always at least two professional meteorologists over–wintering at the station. During the summer they are joined by another two meteorologists from the next expedition and a few meteorologists from the Ukrainian research ship on occasions. A Modular Automatic Weather Station (MAWS) is installed at the Akademik Vernadsky for continuous weather measurements. A MAWS reads the meteorological sensors every 5 seconds and writes averaged and extreme values to a file every 5 minutes. The surface meteorological observations are taken every three hours and at 12, 18 and 00 UTC are sent by HF radio to Rothera where they are transferred to the World Meteorological Centre for use in the analysis and forecasting process. Meteorological measurements and observations for aircraft and vessels are available from Akademik Vernadsky on request. Since surface and forecast weather charts from the Chilean Weather Center are regularly received at the station via radio modem, some short–term forecasts are also available from Akademik Vernadsky.

·                         Almirante Brown. No specific information on forecasting has been obtained.

·                         Palmer. There is a meteorological observing programme at Palmer that provides 6–hourly surface observations that are put onto the GTS. The observations are collected by various base personnel, such as the doctor or communications staff. HRPT and DMSP satellite imagery is collected on the station with the data being archived and returned to the US on tape. Continent–wide isobar charts from the AMRC at the University of Wisconsin are received on a daily basis. There is no weather forecaster at the station.

·                         Matienzo, Melchior,Yelcho and Presidente Gabriel Gonzalez Vidiez are all summer–only bases/refuges.

Mean–monthly MSLP values for Vernadasky Station are shown in Table 7.3.6.4.1 while the mean–monthly station–level pressures for Palmer Station are shown in Table 7.3.6.4.2 (in Appendix 2). Climatologically, there is low pressure in the Bellingshausen Sea and winds from the northwest; however, the complex orography of the region means that the winds experienced at the stations can be quite different. For example, because of the effects of orography, the winds at Akademik Vernadsky tend to be from the north or south. Surface winds from the NWP systems should therefore be used with care. However, changes of wind direction from north to south and vice versa can be predicted once the evolution of the synoptic flow is estimated.

As would be expected, the prevailing northerly winds usually bring mild, moist air southwards, with southerly winds tending to bring dry, cold air northwards. However, returning maritime air on a southerly or returning continental air on a northerly can occur. Returning continental air from the north can bring improving conditions southwards down the western side of the Peninsula.

The average wind speed measured in the Argentine Islands area is about 3 m s^–1 (~6 kt) during the summer and rises to 5–6 m s^–1 (~10–12 kt) in winter time. But gusts can reach 20 m s‑¹ (~40 kt) in the summer and exceed 30 m s^–1 (~60 kt) with a few hours of gale in the winter months. Usually high winds correspond to deep depressions with active atmospheric fronts rapidly moving from the west–northwest. At the same time calm weather is not rare in the region and is observed on up to two to three days per summer month, usually corresponding to a ridge of high pressure over the Antarctic Peninsula.

Upper wind, temperature and humidity

With no radiosonde data available for the region upper–air conditions are predicted using the output of numerical models.

Clouds

Overcast weather dominates this area with the Argentine Islands having 20–25 days per month of overcast conditions year–round with only a few days a month with clear sky. On average, about half of the sky is obscured by low cloudiness, mostly stratocumulus, stratus and nimbostratus. Due to the complex orography, quite low stratus (60–150 m (~200–500 ft)) forms over some places whilst it may be completely clear in others. Multi–layered cloud with precipitation is usual for the region when fronts arriving from the north and north–west are passing over. Sometimes fronts can cause cloudiness lowering to the surface and visibility falling to fog limits.

Cloud is forecast based on satellite imagery and knowledge of the expected changes of air mass as determined from the NWP output.

Visibility: blowing snow and fog

As in the rest of the Peninsula, visibility is usually good, although fog does occur in the Argentine Islands 2–5 times per summer month (November–April) and can be a problem for navigation and flying activities. The formation of fog is aided by the large areas of open water, coupled with the areas of exposed ice. Fog over the Lemaire Channel, French Passage and Penola Strait tends to be rather reluctant to clear in light winds, particularly if temperatures are around zero or above and melt pools have developed on the ice shelves of the islands. Visibility can be less than 1,000 m (~3,300 ft) up to 10–12 days per winter months due to snowfalls and blowing snow.

Surface contrast including white–out

Surface contrast is important mainly for field parties on the islands and the Peninsula, but is not a big problem due to many rocks free from the snow and ice all the year round. Contrast often improves as the summer progresses and more rocks are on the surface.

Horizontal definition

Mainly important for aircraft landing near to Palmer Station on Anvers Island. Predicted based on a knowledge of the forecast cloud amount and type.

Precipitation

Precipitation is produced by depressions and their associated fronts arriving from the north and north–west. The annual total at the Argentine Islands varies from 200 to more than 600 mm. Precipitation is usually in the form of snow or sleet, although rain is quite usual for the summer time and has been reported a few times for the winter. Precipitation of about 40–60 mm is usual for summer months with extreme over 100 mm. The latter mostly due to deep depressions from the South Pacific that determine the weather over the whole Peninsula for 5–7 days and bring heavy precipitation. Although large depressions west of the Peninsula often do not produce any significant precipitation at the Akademik Vernadsky, snow often occurs when the depression is filling and a relatively light pressure gradient develops with snow falling from shallow stratocumulus clouds.

Temperature and chill factor

Mean–monthly maximum and minimum temperatures for Vernadasky Station are shown in Table 7.3.6.4.3 (in Appendix 2) while the mean–monthly temperatures for Palmer Station are shown in Table 7.3.6.4.4 (in Appendix 2) and similar temperature statistics are shown for Almirante Brown Station in Table 7.3.6.4.5 (in Appendix 2). Temperatures in the Argentine Islands are usually within the range –2ºC to +3^oC during the summer months and about 10ºC colder in winter. Annual average temperatures are within –3ºC to –5 C with extreme maximum temperature warmer than +10^o C and minimum colder than –40^oC. The latter extreme was observed in the 1950s and in the last few years minimum temperatures have been much warmer and under –30^oC. Accounting for the wind chill factor above, the equivalent temperatures can be about 5ºC colder in the summer time and 10–15ºC colder in the winter due to more severe winds.

Temperature forecasts tend to be based on continuity and a knowledge of expected changes of air mass.

Icing

With the large amounts of water droplet cloudiness over the region, icing of airframes can be a problem. The same situation can occur in fog for a vessel when supercooled water droplets collide with the surface and turn immediately to clear ice. Although when it occurs it is usually light.

Turbulence

As in other parts of the Peninsula, turbulence mostly can be regarded as being orographically induced. Orographic clouds (altocumulus lenticularis (Ac)) are observed about 4–5 times a month, which points to the presence of mountain waves over the Peninsula.

Hydraulic jumps

Hydraulic jumps have not been reported in this area.

Sea ice

During the last few years sea ice was driven from the Argentine Islands area in December–January and did not form again until April–May. But many big icebergs (20–50 m (~60–160 ft)), growlers, bergy bits and brash ice are observed around Argentine Islands in summer.

Wind waves and swell

No specific information on forecasting has been obtained.