7.3.3                                Greenwich, Robert and Media Luna Islands, South Shetland Islands                          Orography and the local environment.

Greenwich, Robert and Media Luna Islands are located in the South Shetland Island group close to the tip of the Antarctic Peninsula (see Figure 7.3.1 and Figure These islands are southwest of King George Island. The stations covered in this section are:

·                         The Chilean Capitan Arturo Prat Station is on Greenwich Island (62o 30´ S, 59o 41´ W). The station was opened in 1966.

·                         The Chilean Luis Risopatron Station is on Robert Island (62o 22´ S, 59o 40´ W, 40 m AMSL). The station is located on solid rock about 150 m from the coast. Risopatron has been open since 1954. (Prat and Risopatron Stations are about 20 km apart).

·                         The Argentine Cámara Station is on Media Luna Island (62° 36´ S, 59° 54´ W, 22 m AMSL). The station is built on rock 11 km from Prat Station.                          Operational requirements and activities relevant to the forecasting process

None of these stations has an airstrip but forecasts are required for resupply by ship and for activities close to the stations.

·                         The year–round Prat Station has a well–established meteorology programme and climatological data extend back to 1966, although the record is not complete.

·                         Risopatron is concerned with geology/geophysics and terrestrial biology.

·                         Cámara is a summer only station but does make meteorological observations.                          Data sources and services provided

·                         Prat has a year–round surface meteorology programme.

·                         No information is available on Risopatron.

·                         Cámara has a surface meteorology programme.                          Important weather phenomena and forecasting techniques used at the location

General overview

These islands are located in one of the most northerly parts of the Antarctic and have a relatively mild, maritime climate. They are also located at the latitude of the circumpolar trough and are affected my many active frontal depressions that pass through the Drake Passage or enter the Bellingshausen Sea, 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. Precipitation is around 700 mm a year.

Surface Winds and the pressure field

With climatological low–pressure over the Amundsen/Bellingshausen Sea the prevailing wind direction in the area 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

The area is affected by the semi–annual oscillation and surface pressures are lowest (highest) in the spring/autumn (winter and summer) (see Table (in Appendix 2)).

Upper wind, temperature and humidity

No radiosonde ascents are available for the islands so upper fields are predicted using the NWP model output. 


Much of the cloud that affects these islands is frontal in origin, although some non–frontal cloud is also present. Satellite imagery allows the cloud extent and type to be assessed routinely. Prediction of clouds in carried out using satellite imagery.


No specific information on forecasting has been obtained.

Surface contrast including white–out

Surface contrast is important for surface travel on the islands and is predicted based on an estimate of the expected cloud cover.

Horizontal definition

Not relevant on the islands as there are no flying activities.


Precipitation is a frequent occurrence on the islands due to the many depressions that cross the area. It can be predicted using model rain/snowfall fields if available or from the model MSLP fields. In addition, satellite imagery can provide useful information on small synoptic or mesoscale systems that may bring precipitation. In winter most of the precipitation falls as snow, although rain can fall at any time of the year. In summer rain or snow can fall. Table (in Appendix 2) shows the mean precipitation for Prat.

Temperatures and chill factor

At Prat Station the annual mean temperature is usually in the range –1 to –3oC. In summer the mean temperature is one or two degrees above freezing, falling to several degrees or more before freezing in winter. During the winter the temperatures are particularly variable and are heavily dependent on the amount of sea ice present. Over the period 1966–86 the July mean temperature varied between –2.8oC to –12.7oC. Table (in Appendix 2) shows the mean temperature for Prat from 1966 to 1991.


No specific information on forecasting has been obtained.


No specific information on forecasting has been obtained.

Hydraulic jumps

These are not reported on the islands.

Sea ice

Sea ice is highly variable around the islands and both heavy and light ice years are experienced, which can cause problems for ships attempting to re–supply the stations.

Wind waves and swell

No specific information on forecasting has been obtained.