Atmospheric circulations associated to the interannual variability of cumulonimbus cloud frequency in the southern part of Romania

摘要

Especially in summer time, Romania is affected by deep convections associated with severe weather phenomena (hail, wind gusts, flash floods, frequent thunder). The interannual variability of the Cb (cumulonimbus) cloud frequency recorded at 20 weather stations from the southern part of Romania in the 1961-2007 interval was investigated in connection with the atmospheric circulation variability. Using the Canonical Correlation Analysis (CCA) three types of atmospheric circulations have been identified that control about 60% of the interannual variability of the Cb cloud frequency. The three types of identified circulations facilitate warm and moist air advection from the Mediterranean, and cold air advection from northern Europe towards the south of Romania, creating conditions for Cb clouds to occur.