Effect of Long-Term Variations in Wind Regime over Caspian Sea Region on the Evolution of Its Level in 1948–2017

Abstract

The data of atmospheric reanalysis NCEP/NCAR over 1948–2017 (R-1) and NCEP/DOE over 1979–2017 (R-2) have been used to show that variations of the Caspian Sea level are closely correlated with the long-term variations in the field of surface wind in the sea region caused by the transformation of atmospheric circulation over Eurasia. Winds of the eastern and northern rhumbs have been shown to play the main role in variations of evaporation over the Caspian Sea. In the periods of level drop in the Caspian Sea (1948–1976 and 1996–2017), eastern winds dominate, bringing dry and warm air from Central Asia and thus contributing to an increase in water evaporation from the Caspian Sea. In the periods of level rise in the Caspian Sea (1977–1995), northern winds dominate, which cause a decrease in the rate of evaporation. Calculations of evaporation over the Caspian Sea water area using reanalysis data R-1 and R-2 fully confirm these conclusions. A close correlation has been shown to exist between evaporation and the level of the Caspian Sea. The coefficients of correlation between the nonstandardized increments of evaporation and level in the Caspian Sea are –0.86 and –0.75 by R-1 and R-2, respectively. Moreover, the contribution of evaporation to the current drop in the Caspian Sea level by data of improved reanalysis R-2 is greater than that by R-1, because the inflow of air masses from the nearby dry region of the Central Asia according to R-2 has been greater in the recent decade.