Topographic effects on current variability in the Caspian Sea

Satellite-derived surface height fields reveal that variability in the central and southern basins of the Caspian Sea is correlated with topography. Consistently, empirical orthogonal functions from current meter data from the southern basin are aligned with the isobaths. In addition, the gravest mode, which accounts for over 80% of the variance, has an equivalent barotropic structure in the vertical. To what extent this variability can be modeled using a linear analytical model is examined. The latter assumes equivalent barotropic flow aligned with the geostrophic contours, which in turn are dominated by the topography. With ECMWF winds and ETOPO2 topography, the model yields surface height deviations which are significantly correlated with satellite-derived estimates on seasonal and longer time scales in the central basin. The model is somewhat less successful in the southern basin, where the stratification is stronger. Nevertheless, the results are encouraging, given the extreme simplicity of the model.