5. Caspian Sea
5.1. Satellite data
By convention, the Caspian Sea is divided into the Northern (1), Middle (2) and Southern (3) regions (Fig.23). The Northern Caspian is the shelf area which depth is less than 10 m. This region is under strong influence of river run-off; the largest European river Volga flows into the Northern Caspian, the Ural and Terek rivers too. About 90% of the total river discharge in the Caspian Sea falls within the Northern region.
The Middle Caspian is also influenced by the Volga river run-off. The Volga waters move mainly south along the western coast of the Caspian Sea and turn eastward near Apsheron forming cyclonic circulation in the Middle Caspian. The other part of the Volga waters comes into the Southern Caspian; this region is also influenced by the run-off of the Kura river and the rivers flowing down the Iranian coast.
Fig.24 shows the monthly coverage of the regions in the Caspian Sea by SeaWiFS data and MODIS-Aqua data in 1998-2010. Kara Bogaz Gol, a very specific gulf with salinity of 300‰, is not considered here. The coverage of less than 50% occurred in cold months in the Northern Caspian. Although such data were included in data processing and further analysis, the obtained results for these cases cannot be considered as reliable.