Seasonal variability of the Caspian Sea three-dimensional circulation, sea level and air-sea interaction

Abstract

Abstract. A three-dimensional primitive equation model including sea ice thermodynamics and air-sea interaction is used to study seasonal circulation and water mass variability in the Caspian Sea under the influence of realistic mass, momentum and heat fluxes. River discharges, precipitation, radiation and wind stress are seasonally specified in the model, based on available data sets. The evaporation rate, sensible and latent heat fluxes at the sea surface are computed interactively through an atmospheric boundary layer sub-model, using the ECMWF-ERA15 re-analysis atmospheric data and model generated sea surface temperature. The model successfully simulates sea-level changes and baroclinic circulation/mixing features with forcing specified for a selected year. The results suggest that the seasonal cycle of wind stress is crucial in producing basin circulation. Seasonal cycle of sea surface currents presents three types: cyclonic gyres in December–January; Eckman south-, south-westward drift in February–July embedded by western and eastern southward coastal currents and transition type in August–November. Western and eastern northward sub-surface coastal currents being a result of coastal local dynamics at the same time play an important role in meridional redistribution of water masses. An important part of the work is the simulation of sea surface topography, yielding verifiable results in terms of sea level. Model successfully reproduces sea level variability for four coastal points, where the observed data are available. Analyses of heat and water budgets confirm climatologic estimates of heat and moisture fluxes at the sea surface. Experiments performed with variations in external forcing suggest a sensitive response of the circulation and the water budget to atmospheric and river forcing.

Some aspects of the deep abyssal overflow between the middle and southern basins of the Caspian Sea

“…The sea surface temperature (SST) in the northern basin ranges from below zero under frozen ice in winter to 25-26 °C in 15 summer, while more moderate variability occurs in the southern basin changing from 7-10 °C in winter to 25-29 °C in summer (Ibrayev et al, 2010). To illustrate the differences of surface temperatures of the middle, southern, and northern basins in various seasons, time series of surface temperatures are plotted using MODIS data from 2014 to 2015 in figure 1.…”

“…The Caspian Sea is enclosed with tides being fairly weak and circulation in this sea is mainly due to wind and buoyancy, although some wave-driven flows also occur in coastal regions [Bondarenko, 1993;Ghaffari and Chegini, 2010;Ghaffari et 30 al., 2013;Ibrayev et al, 2010;Terziev et al, 1992]. The seasonal circulation based on a coupled sea hydrodynamics, air-sea interaction and sea ice thermodynamics model of the Caspian Sea was investigated by Ibrayev et al (2010) and Gunduz and Özsoy, 2014).…”

“…The seasonal circulation based on a coupled sea hydrodynamics, air-sea interaction and sea ice thermodynamics model of the Caspian Sea was investigated by Ibrayev et al (2010) and Gunduz and Özsoy, 2014). The effect of fresh water inflow to the Caspian Sea on seasonal variations of salinity and circulation (or flow) Ocean Sci.…”

Toward the S3DVAR data assimilation software for the Caspian Sea

“…The background data (defined in (1)) we consider are provided by the software ROMS [3]. The satellite observations (defined in (2) [4]. The preconditioning approach for V i we used is the EOFs method [16] which is based on a Truncated Singular Value Decomposition (TSVD) of the matrix.…”

“…The SST variabilities in the Caspian Sea have different characteristics in the different regions [4]. Caused their diversities, sometimes the studies focus on the North Caspian or South Caspian separately.…”