Physical Oceanography, Vol. 19, No. 4, 2009
ANALYSIS OF OBSERVATIONS AND METHODS FOR CALCULATING
HYDROPHYSICAL FIELDS IN THE OCEAN
STATISTICS OF MESOSCALE CYCLONIC EDDIES OVER THE BLACK SEA
V. V. Efimov,
M. V. Shokurov,
D. A. Yarovaya,
and D. Hein
On the basis of the results obtained by using the PRECIS regional climate model with high space
we study the mesoscale specific features of the atmospheric circulation in the
Black-Sea region for a period of
yr. To separate and trace the subsynoptic eddies, we use a
method based on the Okubo–Weiss criterion. Several types of cyclonic eddies are selected and
described: winter Caucasian coastal eddies, summer Caucasian separated eddies, cyclonic eddies
of the open sea, and seldom quasitropical cyclones. For various types of eddies, we present the
statistics of their lifetime and intensity and the histograms of diurnal and seasonal cycles.
The atmospheric circulation in the Black-Sea region suffers the influence of several determining factors.
First, we can mention large-scale synoptic cyclones formed, as a rule, in the North Atlantic and moving to the
west through Europe or over the Mediterranean Sea toward the Black Sea. Their characteristic space scales are
and their lifetime can be estimated as
3–5 days. The maximum development of these cyclones is
observed in the winter season, and their propagation paths largely depend on the determining influence of the
North-Atlantic Oscillation. The statistics of their stormtracks is fairly well described in the literature (see, e.g.,
). Synoptic cyclones of this type are the main synoptic processes of the extratropical latitudes. For the Black-
Sea region, they can be regarded as external phenomena.
At the same time, the regional specific features of the orography of the Black-Sea region, such as the pre-
sence of sufficiently high mountains surrounding the sea and the Black Sea itself introduce mesoscale distur-
bances in the atmospheric circulation and, in particular, affect the processes of formation and development of the
cyclones. These phenomena were studied for the neighboring Mediterranean basin. Thus, three characteristic
mechanisms of the development of cyclones in this region were described in . The first mechanism corres-
ponds to the case of weak and small cyclones for which the anomaly of potential vorticity in the upper tropo-
sphere is small or absent, and the initial disturbances in the lower levels caused, e.g., by orography or the anoma-
lies of the surface temperature do not develop in the course of subsequent evolution. The second mechanism is
most widespread and can be regarded as classical under the conditions of the open ocean. This mechanism de-
scribes the cyclones excited by the anomalies of potential vorticity as a result of the advection of cold air in the
upper troposphere and developing in the frontal zones. Finally, the third mechanism corresponds to the regional
cyclones most rapidly developing from the initial disturbances in the lower troposphere. These cyclones are
Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol, Ukraine.
Hadley Centre Met Office and University of Reading, Reading, UK.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
19–33, July–August, 2009. Original article submitted April 22, 2008;
revision submitted June 12, 2008.
0928-5105/09/1904–0211 © 2009 Springer Science+Business Media, Inc. 211