Physical Oceanography, Vol.
5, January, 2012 (Ukrainian Original No.
5, September–October, 2011)
EVALUATION OF THE COEFFICIENTS OF HORIZONTAL EXCHANGE IN THE
BLACK SEA ACCORDING TO THE DATA OF DRIFTER EXPERIMENTS
A. E. Pogrebnoy
We generalize the method used for the evaluation of the coefficients of horizontal diffusion of Brownian
particles to the nonstationary case, as applied to the drifter experiments. The limits of applicability of
the proposed procedure are determined. The coefficients of horizontal exchange are computed with an
aim to compare them with the estimates obtained earlier by using the generalized Taylor theory. The
mutual agreement of these estimates is demonstrated. It is shown that the difference between the values
of the zonal (0.19·10
/sec) and meridional (0.11·10
/sec) coefficients of exchange in the Black Sea
cannot be explained by the effect of increase in the longitudinal component of pulsations of the velocity
as a result of its transverse shear relative to the mean current. A conclusion is made that the processes of
horizontal exchange in the Black Sea are geographically anisotropic.
Keywords: coefficient of horizontal exchange, drifter.
The analysis of the images obtained by artificial satellites of the Earth in the infrared and visible spectra
shows that the circulation of surface waters in the Black Sea can be regarded as a collection of currents of vari-
ous space and time scales. Thus, the set of macroscopic motions include, first of all, the Rim Current  flow-
ing along the coast over the continental slope in the cyclonic direction and the east and west cyclonic gyres lo-
cated in the abyssal part of the sea. In addition to the indicated macroscale currents, we also detect mesoscale
motions in the form of eddies. The direction of rotation of these eddies is, as a rule, anticyclonic. It seems like-
ly that they can play an important role in the formation and transformation of the vertical stratification of hydro-
physical fields in the upper layer of the sea and participate in the realization of the effective horizontal (lateral)
To estimate the intensity of horizontal exchange in the Black Sea, it is possible to use the data of large-scale
international drifter experiments originated in 1999. A drifter is made in the form of a surface float equipped
with a drogue. The drogue is located at a depth of 15
m and its hydrodynamic drag is 40 times higher than the
hydrodynamic drag of the float. Thus, the influence of surface waves and wind-induced drift currents on the
horizontal displacements of the drifter is insignificant. The location of the drifter is determined by the volume
of water surrounding its drogue. The data about the location of the drifter (together with the additional data on
the characteristics of the surface layer of the sea) are transferred from the drifter to satellites and then recorded at
the data-processing center. In this case, the accuracy of determination of the geographic coordinates is equal to
several hundred meters and the frequency of observations varies within the range 4–6 measurements per day.
The most well-known method used for the evaluation of exchange coefficients according to the statistical
characteristics of Lagrange particles is the Taylor theory  in which the required exchange coefficient is given
by the formula
Marine Hydrophysical Institute, Ukrainian National Academy of Sciences, Sevastopol, Ukraine.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
40–49, September–October, 2011. Original article submitted April 21,
2010; revision submitted May 20, 2010.
0928–5105/12/2105–0329 © 2012 Springer Science+Business Media, Inc. 329