CHARACTERISTICS OF PRECIPITATIONS DISTRIBUTION INDUCED BY CUT-OFF LOW CYCLONE ACTIVITY IN ROMANIA DURING THE WARM SEMESTER.

Cut-off low altitude cyclones (COLs) are characterized by the presence of small cold air masses detached from the polar vortex as a consequence of Rossby waves development. Their displacement at a lower latitude is capable to induce higher atmospheric instability and they have a great influence on the amount of precipitation over Romania between April and September. This paper is based on the analysis from a synoptic point of view of the days when the precipitation amount was greater than 10 mm between 1961 and 2010, during the warm semester (April - September). Sea level pressure maps from Deutsche Wetterdienst and 500 hPa geopotential height from Climate Forecast Systems of NOAA, available at www.wetter3.de, the GFS forecasting numerical model (Global Forecast System) were used for the synoptic analysis. This study, by analyzing all days with the amount of rainfall greater than 10 mm, and by making all the cartographic materials presented, aims to highlight the most affected areas by them, using ROCADA dataset. Out of the total of 5,340 days with the precipitation amount greater than 10 mm at the level of Romania, 1498 of them (28%) are associated with COLs activity. In April, 74 days (4.94%) with COLs activity were found. Starting May, the COLs activity is much better evidenced, being present in 220 days (14.69%), in June 408 days (27.24%) and 437 days in July (29.17%). In August, with 252 days (16.82%) and in September with 107 days (7.14%), the COLs activity started to decrease. [ABSTRACT FROM AUTHOR]