Numerical Simulation on the Diurnal Variation of Precipitation over Northeastern Bangladesh: A Case Study of an Active Period 14-21 June 1995

The diurnal variation of precipitation over the Bengal region is numerically investigated using a non-hydrostatic mesoscale model. We focused on northeastern Bangladesh, where the maximum of late night-early morning precipitation is observed. Simulated characteristics of diurnal variation of precipitation agree, to a large extent, with observable evidence. The mechanism of the high late night-early morning precipitation in a case of June 14 to 21 is investigated using the model results. At night, strong southwesterly monsoon winds transport a large amount of moisture over Bangladesh. This high equivalent potential temperature (theta(e)) air mass climbs the slope of the Meghalaya Plateau or climbs over a deep (several hundreds meters to 1 km) pool of cold air, and triggers precipitation over northeastern Bangladesh. The triggered systems develop into mesoscale squall lines and propagate southward or southsouthwestward at a speed of about 10 m s(-1). It is found that the katabatic mountain wind is not a major player in the diurnal variation of precipitation over the northeastern Bangladesh area.