Relationship between Widespread Low Extreme Temperatures in Azerbaijan and Circulation Patterns of 500 hpa Level in Cold Period

In this paper we have determined the widespread low extreme temperatures of cold periods in Azerbaijan region using Normalized Temperature Deviation Index (NTDI). With an emphasis on (NTDI) 80 low extreme temperature days were selected for the study. For the recognition of circulation patterns that generate extreme temperatures in these 80 days, we made an 80-day matrix having 943 nodes from the geo-potential height data in 500 hpa and 0-100 degrees longitudes and 15-70 degrees of latitudes.Ward cluster analysis of the matrix led to the recognition of 7 circulation patterns influencing the creation of extreme temperatures. Among these patterns, the No. 1 circulation pattern with the 24-day frequency (out of 80 days) having 30% of contribution i.e., the highest contribution, and pattern No. 6 with a 3 day frequency (out of 80 days), having the 3.75% of contribution showed the lowest contribution in the creation of extreme temperatures in Azerbaijan. The study of geo-potential elevation in 500 hpa contours during 80 days indicate that extreme temperatures of Azerbaijan are affected by topographic patterns of 500 hpa contours. Wind direction and the spell of cold air to the area also in harmony with the same contour patterns leads to the movement of cold heavy air of higher latitudes to the area of study and thereby, the creation of extreme temperatures. Out of 8 known circulation patterns that transfer the cold air from higher latitudes to the Azerbaijan area, in 7 patterns the long plunges are observed and in the circulation pattern No. 6 there exists a deep cyclone that acts like a cold depression and establishes the stability of cold air continuation over the area and therefore, make extreme values in temperature. Paying attention to the role of cold winds in 80 selected days for the study it became clear that coldness or the extreme cold temperatures in this area were resulted from downward movement or the transfer of the cold air while even one radiation coldness was not observed in the whole 80-day study period.