Estimation of the freezing period in the Baydaratskay Bay (see the location of the two ERS-1 SAR images ) is based on statistical data, especially the continuous series of satellite data starting in 1979. These data show that the most important freezing period in the bay is from week 42 to 45 (mid October to early November). In some years the freezing period was 3-4 weeks later. Russian observations, which started in 1920, show that freezing can start as early as week 40 (first week of October). In 1993 SAR images from ERS-1, combined with meteorological data, were used to monitor the freeze-up period more accurately.
The two images show a characteristic behavior of the freezing process. During southwesterly winds ice is formed first on the eastern coast. On November 1 (left) most of the bay is open water with stripes of grease ice oriented parallel to the wind direction. The ice is accumulated in the down-wind direction and in the following two weeks the ice cover grows towards the west. On November 17 (right) only a narrow band of open water (bright signature) is still present.
The freeze-up of the bay can be delayed if the trajectory of the low pressure systems in November goes from the Svalbard area towards Severnya Zemlya, causing southwesterly warm winds over the bay. The ice edge in the Kara Sea is pushed towards NE and the cooling of the water and the associated ice formation is delayed. This situation can be monitored by meteorological data satellite ice maps. The ocean temperature data will show a delay of the cooling in the water column. The low pressure trajectories, as soon as they have been established, tend to follow the route from Svalbard and eastwards for some weeks, especially if there is a strong high pressure sitting over central Russia. This was the case in November 1993 when the western side of the bay was kept icefree for several weeks.
Early freeze-up has not been observed in the last 15 years. A situation which will encourage early freeze-up is that a high pressure is sitting over the Kara Sea and Barents Sea region during September and beginning of October. The high pressure will generate cold air masses which cools the water column to the freezing point within a couple of weeks. Ice formation can then start in early October. However, if early freezing occurs, there is some probability that the ice concentration only reaches 60 - 80%, or if it goes up to 90 - 100% it will be reduced again after a few weeks. This will be the case if the high pressure over the Kara Sea disappears and is replaced by a series of eastward moving low pressures.

NERSC, Bergen, Norway

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry