A note on propagating rainfall episodes over the Bay of Bengal

An observational analysis of precipitation episodes over the Bay of Bengal and the adjacent coastal region is conducted using the TRMM Real-Time Multi-Satellite Precipitation Analysis (MPA-RT) products for three warm seasons (i.e. May to September for 2002-2004). Time-distance diagrams (Hovmüller diagrams) of rainfall episodes reveal frequent travelling precipitation episodes having lifetimes greatly exceeding those of individual convective systems. The majority of the episodes translate southward and many do not appear to have a steering level (i.e. they propagate in a hydraulic-like manner), unlike those previously documented over midlatitude and tropical continents which usually have a steering level. On average, the coherent systems have a latitudinal span of 5 degrees and a 1-day duration and a meridional propagation speed of 8 m s^-1, approximately. The episodes mostly initiate over the coastal land around midday and offshore around midnight.