The northward propagating envelope of convection during JASMINE

Infrared brightness temperatures from the Meteosat-5 geostationary satellite indicate that the Bay of Bengal was under suppressed convection conditions during the first half followed by highly convective conditions during the latter half of the May to early June Joint Air-Sea Monsoon Interaction Experiment (JASMINE). Time-latitude sections along the Bay of Bengal suggest that strong mesoscale storms are modulated by a northward propagating envelope of convection. The envelope of convection moves northward across the Bay of Bengal at a rate of about 1.5° per day. Such northward propagating large-scale features, in conjunction with an eastward propagation of convection along the equator, are commonly observed during boreal summer on timescales of 30-40 days. The northward propagating event observed during JASMINE is examined in terms of its impact on the South Asian monsoon onset and in the context of present theories regarding the evolution of the boreal summer Intraseasonal Oscillation (ISO). Special attention is paid to the coupled ocean/atmosphere variability on the ISO timescale.