Structure of the Coastal Current Direction Bimodality at the Southern Coast of Crimea in 2002–2008

This paper aims at improvement of knowledge about the structure of bimodal distribution of coastal current direction repeatability at Cape Kikineiz of the Southern coast of Crimea as per monitoring data obtained at the stationary oceanographic platform of the Black Sea hydrophysical sub-satellite testing area of the MHI RAS. Used for monitoring, a vertical measuring antenna with a fixed aperture of Euler testers of the current horizontal component provided verifiable and synchronic isolation of the current's structural characteristics with a vertical velocity shift and multiscale coherent oscillations of the current. New results of analysis of in situ data are presented regarding characteristics of the coastal current and its variability. The data were obtained within the period from November 2001 to 2008. Change patterns of the long-term coastal current regime are noted. The current's characteristics are matched to the results obtained at Cape Kikineiz of the Southern coast of Crimea for the period from September 2008 to 2019. Regular intense oscillations of the coastal current at the local inertial (17 hrs) and daily component as well as current oscillations with a period of 11.6 day are defined. Evolution is analyzed of probability density distribution of the velocity module and current vector direction after calculations, during which a corresponding vector distribution of intensive inertial-gravitational, mesoscale and synoptic oscillations was excluded in the original vector series of dynamics using a digital filtration method. When excluding the contribution of daily and inertial oscillations, the backward and primary mode ratio in the histograms of the coastal current direction repeatability decreases by more than three times. When excluding the contribution of mesoscale and synoptical oscillations, the backward mode of current is almost absent and there exists only a large-scale coastal current coinciding with a cyclonic direction of the coastal edge of the Black Sea Rim Current. Bimodal distribution of the coastal current direction repeatability is a result of superposition of velocity vectors of a large-scale current and variable contribution of existing orbital velocities of multiscale wave and vortex formations present in the coastal-shelf area.