Temperature structure and wind-induced water level anomalies in the Caspian Sea: A study on coastal upwelling

Abstract

In this study, the index of coastal upwelling was examined based on wind-induced water level anomaly using the Princeton ocean model (POM) in the Caspian Sea. The data of wind fields and atmospheric fluxes were obtained from European Centre for Medium-Range Weather Forecasts (ECMWF) database and considering freshwater inflows in the Volga, Kura, and Ural Rivers. This model was implemented for 10 years, from 2008 to 2017. Findings indicated that winds, currents, water levels, and sea surface temperatures are highly correlated in upwelling events. Ekman transport and surface geostrophic current (southward) occur due to wind field and water level anomaly (about 10 cm, between the coastal and offshore areas) in the eastern shores of the middle basin, respectively. Partial and full coastal upwelling mainly occur in the cold and warm months, respectively, in the middle basin (upwelling center). So, in June, July, and August, on the eastern shores of the middle and southern basins, a greater number of water level declines occurred, and the upwelling index increased compared to other months. Topography and the weak wind field effects can be the mechanism causing the occurrence of partial coastal upwelling. Also, the findings implied that seawater temperature anomalies are higher in the windy state in both June and January compared to calm situations. The intensity of sea current in the windy state in the warm months is less than in the cold months due to the weak counter-clockwise circulation.