Large-Scale Features of the Novorossiysk Bora

Abstract

On the basis of the reanalysis data with high spatial resolution and 36 years temporal coverage the spatial structure of wind speed and temperature fields in the Black Sea region for bora events in winter months was assessed. It is shown that bora development is followed by a formation of large-scale cyclonic circulation in the southeast part of the Black Sea. The airflow of the northwest edge of high Caucasus Mountains leads to the wind speed cyclonic vorticity over the sea; high Anatolian mountains block propagation of the air flows to the south and, thus, they jointly form a large-scale closed circulation cell. Regression dependences between the wind speed and temperature in Novorossiysk region are studied; they show that in winter strong northeast winds correspond to frontal-type bora activity which is accompanied by the air temperature decrease. The important feature of the temperature field during bora is revealed at that: temperature in the sea coastal area exceeds the one in the mainland foothill part of the region. For studying the physical mechanism of this phenomenon the atmospheric circulation computation (using WRF-ARW model) for specific Novorossiysk region bora event, which provided a detailed consideration of vertical structure components of wind speed and potential temperature in the coastal zone, above the sea, above the mountains and in the foothill mainland of the region, was carried out. It is shown that the mechanism of higher temperature formation in the sea coastal area is related to the air blocking above the windward slope of the mountain ridge and its replacement with warmer air from the upper layers of the atmosphere at the leeward slope.

Keywords

Novorossiysk region, bora, WRF-ARW model of atmospheric circulation, cyclonic vorticity.

DOI: 10.22449/1573-160X-2017-4-26-34

Download the article