Nocturnal jet and its effects on early morning rainfall peak over northeastern Bangladesh during the summer monsoon season

Diurnal variations of rainfall and upper wind over Bangladesh during the summer monsoon season were investigated through the data analysis of raingauge, 4-times-daily rawinsonde and pilot balloon observations. Over the northeastern part where the total monsoon rainfall is heavy a rainfall peak appears at 3 to 6 local time in the early morning. In the lower troposphere, the southeasterly accelerates in the evening, and the wind direction exhibits a clockwise change at night. This feature corresponds with the nocturnal jet, which can be a cause of the midnight-early morning rainfall peak in the northeastern part of Bangladesh through the increased wind blowing against the southern edge of the Meghalaya Mountains.