bora(redirected from Bora (disambiguation))
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a strong and gusty wind, blowing primarily during the cold season down mountain slopes; it produces significant cooling (as opposed to the foehn). It occurs where low mountain ridges border a warm sea: for example, the Adriatic coast in Yugoslavia near Trieste, the north shore of the Black Sea between Tuapse and Novorossiisk in the Caucasus, and especially in Novorossiisk itself (where it is called the nord-ost), on the shores of Lake Baikal (sarma), on Novaia Zemlia, and elsewhere. The bora is formed when an invading cold air mass, which while passing over a low ridge is only slightly warmed adiabatically, then “drops” rapidly along the lee side of the slope because of the pressure gradient and force of gravity. The bora often produces catastrophic results (for example, the icing of vessels). In Novorossiisk, there are on the average 46 days annually where bora conditions prevail (mostly during November and March); individual boras last two to three days (sometimes up to one week), the wind reaches a velocity of 40 m/sec (at the Markotkhinskii pass near Novorossiisk, 60 m/sec and more).
S. P. KHROMOV