Characteristics of the mixing effect of small-scale internal waves in the upper layer of the Black Sea according to the data of fine-structure sounding

Abstract

--A method of statistical separation of fine-structure fluctuations according to their origin is applied to the analysis of the characteristics of mixing in a layer located below the summer temperature minimum in the Black Sea. The simplification of the procedure of numerical evaluation of the coefficient of vertical wave exchange enabled us to perform the comprehensive fine-structure processing of the data of regular surveys of the Black Sea with an aim to determine the spatial distribution of the field intensity of small-scale internal waves and the intensity of mixing caused by these waves in the analyzed layer.Actually, the fine vertical structure of hydrophysical fields in the ocean contains information about the characteristics of dynamic processes participating in the formation of this structure. Among these processes, one should especially mention internal waves, advective motions, and convection caused by double diffusion. However, the results of action of various mechanisms of structure formation at each point of the measured profiles of temperature, salinity, and density are superimposed in a complex chaotic way, which makes the process of their analysis quite complicated.Up to now, the principal achievements in this field are connected with the development of methods for the classification of the types of fine vertical structures on the basis of some their parameters determining the relative roles of various dynamic factors in the formation of fine-structure inhomogeneities. The classification is performed qualitatively according to the degree of closeness of observed structures to certain model types [1].The relationship between the characteristics of fine structures and wave and turbulent processes was studied in [2]. An important role of small-scale internal waves in variations of the intensity of fine-structure fluctuations over the field of a synoptic vortex is demonstrated in [3].Depending on the mechanisms of formation, the method of differential approach to the spectral composition of thin thermohalinic inhomogeneities in the ocean is based on the joint analysis of the spectra of temperature, salinity, and density calculated in a segment of the vertical profile where the average gradients of all three parameters vary insignificantly [4].There are various models used to separate the contributions of advection, internal waves, and double-diffusion convection to the fine-structure dispersions of temperature, salinity, and density. Thus, the first model of separation takes into account * Translated by Peter V. Malyshev and Dmitry V. Malyshev UDC 551At65.15