Investigation of physical properties and long coastal waves in the southern Caspian Sea

The Caspian Sea, the world’s largest inland enclosed water body, consists of three basins namely northern, middle and southern. This study investigates physical oceanography properties and long waves in the southern Caspian Sea. To deal with this, we used ADCP, CTD, weather data, sea level and satellite imageries. The data were collected by National Institute of Oceanography and Atmospheric Sciences (ADCP and CTD), Port and Maritime Organization (sea level), and Meteorological Organization (wind data). The results show that the temperature plays pivotal role in the structure of water in this basin. The place of thermocline and pycnocline are about at the same depth and the thickness of mixed layer in the summer and fall are about 25 and 15 meters, respectively. The analyses of ADCP data show that thermocline disappears from February to March and after two months, the thermocline starts to develop. In most of cases, the magnitude of meridianal velocity is stronger than zonal speed based on ADCP data. Spectral density of time variations of velocities of current and wind show that there are many peaks from a few hours to many days. We consider some periods such as 30, 40, 48 and 60 hours as Kelvin waves based on our background information about these waves. Sea level data and satellite images (Aviso sensor) confirm the results in terms of periods and wavelengths. Due to barotropic and baroclinic modes of Kelvin waves, wavelengths, angular frequencies and group speeds are calculated separately. According to these results, baroclinic mode is more important than barotropic mode in this basin. Based on the governing equations of shallow water, the sea level gradient equation was written and time series of sea surface level changes were plotted. The results show that the long wave amplitudes are from 10 to 15 cm according to satellite and observation data. In this basin, the reduced gravity varies from 0.006 to 0.008 m/s2 in different seasons and the thickness of the denser water column is considered about 150-200 m. The Rossby radius of deformation and group velocity are 20 km and 1.2 m/s, respectively. Due to different periods of Kelvin waves, the wavelengths vary from 129 to 259 km. The satellite images confirm Kelvin waves because there are some anomalies in sea level similar to that produced by Kelvin waves with similar periods and wavelengths. Based on results, it is recommended that more detailed observational data should be collected in the deep parts of the southern and middle basins of the Caspian Sea