Convective Bands as Structural Components of an Arabian Sea Convective Cloud Cluster

During the summer Monsoon Experiment 1979 (MONEX-79) a unique mix of meteorological data was obtained on 20 June to analyze a convective cloud cluster that formed over the extreme eastern Arabian Sea. An analysis of the available data revealed the existence of several convective bands (as well as other types of convection) in the cloud cluster. The convective bands formed and decayed as a result of complex interactions between synoptic-scale features [low-level westerly jet and upper-level tropical easterly jet (TEJ)], mesoscale features (mesoscale downdrafts and mesoscale wind variability), and convective-scale features (convective updrafts and downdrafts). The observed southeasterly propagation of the convective bands on 20 June was explained through an examination of the thermodynamics of the updrafts and downdrafts on various scales. A comparison was made between the Arabian Sea convective bands and those observed in the GATE (Global Atmospheric Research Program's Atlantic Tropical Experiment). Some differences were noted. The Arabian Sea convective bands existed in a highly sheared environment, with the high-energy southwesterly inflow just underneath anvils being blown westward by the TEJ. Such an arrangement of low- and upper-level Arabian Sea winds restricts the lifespan of a convective band by limiting the supply of high-energy air from low levels.