Diurnal variations of cloud activity in Bangladesh and north of the Bay of Bengal in 2000

Abstract

The Japanese Geostationary Meteorological Satellite (GMS-5) high resolution (10 km mesh) hourly data are sampled in 1°×1° grid boxes in the domain of 600×600 km over Bangladesh (land) and the north part of the Bay of Bengal (ocean) to obtain diurnal cycle of cloud activity. The cloud embedded area (CEA) shows afternoon (∼1700 LST) and morning (∼0003 LST) peaks over land typically composed of relatively small deep (<214 K) and large shallow (<243 K) convective cloud systems. In contrast, only afternoon (1400–1600 LST) peak is observed over ocean typically composed of small shallow and large deep convective cloud systems. Meanwhile the frequency of the cloud systems exhibits the clear afternoon (∼1600 LST) peak over the land and the ocean that indicates that afternoon is the initiation times of land-based clusters over Bangladesh and water-based clusters in the analyzed ocean (87.44–93.33°E; 15.7–21.08°N). Radar data from Bangladesh Meteorological Department (BMD) for consecutive 135 days from 16 April 2000 over Bangladesh are utilized to obtain the diurnal variations and characteristics of precipitation in relation to cloud activity. The nature of the diurnal cycle of precipitation in Bangladesh is that there is a morning peak at 0600 LST with minimum at noon. The frequency of the echoes exhibits two peaks—one in the afternoon (∼1500 LST) and the other in the morning (0600 LST) hours. The smaller echoes dominate in the afternoon while larger echoes develop in the early morning. The shape, lifetime, horizontal length and movement of the precipitation features in Bangladesh are also investigated using radar data.