Numerical modeling of physical properties, currents and eddies in the Southern Caspian Sea

The Caspian Sea is the greatest lake in the world. This basin plays a significant role in the climate of the countries located in the vicinity of it. This water body is divided into three basins, including the northern, middle, and southern parts. The Iranian coasts are located in the southern part. This paper uses the ROMS model to investigate the seasonal changes in physical oceanography phenomena in the Southern Caspian Sea. To deal with this, the model was run for seven years. The GEBCO data are utilized to make the grid file with the resolution of 30 seconds. Three-hourly ECMWF (ERA Interim) data was applied to the model. Furthermore, the Kura and the Sepidrud rivers were considered for simulation. The climatology and initial conditions data were extracted from World Ocean Atlas 2013 and ICOADS, respectively. In this research, the horizontal resolution of 2.5 km and 16 layers in vertical grids were applied to the model. The model outputs are validated with observation data and other simulations in this basin. The results show that the ROMS can be an appropriate model for simulation in this region, particularly in the southern part, as the outputs are compatible with the observation data. Moreover, the results indicate that the seasonal changes of temperature are remarkable compared to salinity.     While the model has recorded the mean value of 16°-18° C for temperature, this value for salinity is 13.5 PSU. The typical surface currents are counter-clockwise as the dominant winds are from the north to the south towards the Iranian coasts. The topography of the southern part controls these currents because most eddies are formed in the vicinity of the deep part of the south part. Some eddies are dipoles that can be observable in most seasons. The strongest eddies are formed in this basin in the fall, particularly in December. The most important finding of this research can be the fluctuation of the surface water, which varies from 5 to 10 cm, due to these cyclonic and anticyclonic eddies. When eddies are cyclonic, they form the center of cold water. This water mass can be 0.5°-1° C colder than the surrounded water. Herein, we conclude that these eddies can have two considerable effects on sea surface temperature distributions and sea surface height. Thus, this model shows the behaviors of eddies correctly. It should be noted that eddies can play a significant role in the propagation of oil spills in the southern parts, which is discussed in this paper.