M.A. Farukh, M.A.M. Hossen, M.A. Badhan, M.S.H. Sarker and A.C. Das
Cyclones have occurred more frequently in recent decades in a disaster-prone country like Bangladesh. Twenty-two (22) extreme cyclone events that occurred from 1975-2014 were investigated in this study with respect to air temperature climatology. Air temperature, sea level pressure, rainfall, relative humidity (Rhum), and sunshine hours (SShr) have been analyzed to find out the impact of air temperatures behind cyclogenesis. Historical cyclone data were obtained from Bangladesh Meteorological Department; Bangladesh Bureau of Statistics and Disaster Preparedness Centre (AIT). Historical weather data was collected from the Climate Division of BMD. Principal Component Analysis (PCA) and Clustering were used to find out the whole atmospheric air temperature impact on cyclogenesis. The NCEP–NCAR reanalysis data were used to find out the distribution of air temperature anomaly over Bangladesh and Bay of Bengal (BB). Among the 22 cyclones, cluster 2 belongs to 9 cyclones and cluster 3 comprises of 12 cyclones. Clusters 2 and 3 indicate that temperatures of about 34 to 35°C were mostly responsible for the formation of a total of 21 cyclones from 1975 to 2014. The existence of a relatively cooler zone (strong negative anomaly) near to surface level, in association with a relatively warmer zone (strong positive anomaly) at 850, 700, 500, and 300hPa level were firmly responsible for cyclogenesis over BB. The larger, warmer air mass in the upper atmosphere could have a significant impact on the development of huge instability throughout the entire atmospheric column, potentially leading to the formation of extreme weather phenomena such as severe cyclones in southern Bangladesh.
Keywords: Air temperature anomaly; Clustering; Cyclogenesis; Synoptic climatology.