Ice Conditions from Historical and Satellite Observations

Abstract

We address spatial and temporal variability of ice conditions in the Aral Sea from historical observations and recent satellite microwave observations. A short description of the historical evolution of the Aral Sea since the mid-twentieth century is given, as well as recent activities related to the dam in the Berg strait. An overview of historical observations of the ice regime at the coastal stations and using aerial surveys is provided. The lack of reliable in situ measurements and time series for ice cover parameters since the mid-1980s may be successfully overcome by using active and passive microwave satellite observations, which provide reliable, regular, frequent, and weather-independent data. An ice discrimination methodology, based on the synergy of active and passive data from radar altimeters TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On (GFO) satellites, as well as the SMMR and SSM/I radiometers is presented. This methodology has been applied to the entire satellite dataset to define specific dates of ice events (first appearance of ice, formation of stable ice cover, appearance of open water and the complete disappearance of ice) for both the Small Aral and Eastern Large Aral. The resulting time series of ice cover parameters are analysed in the context of available in situ observations. First we complement historical observations by satellite imagery in the visible range to illustrate spatial patterns in ice formation, development and decay prior to the late 1980s and in recent time. Then we address interannual variability of timing of ice events and severity of ice conditions since the earliest coastal observations (1940s) until now (2006/2007). Finally, we discuss temporal variability of ice regime parameters in the context of air temperature, bottom morphology and salinity changes.