Impact of Arabian Sea pollutions on the Bay of Bengal winter monsoon rains

Abstract

Accumulation of pollution over the southern Arabian Sea has been documented in numerous studies that followed the INDOEX field project of 1992. In this paper we show several examples of this feature from the MODIS/CALIPSO data sets. We identify this feature as the Bombay Plume that makes its way into the Arabian Sea from the west coast of India. A second part of this work is on the modeling of the impacts of pollutions. For this purpose we use a NASA Goddard Earth Observing System (GEOS) model to carry out many comparative forecast experiments that include the pollution based on MODIS and control runs that utilize climatological estimates of pollutions. The model includes both the direct and indirect effects of aerosols. We noted that: a) The Arabian Sea experience above normal rain during these periods for the MODIS experiments as compared to the control. b) The most interesting feature in these results is the documentation of a divergent outflow center, in the upper troposphere, over regions of the Arabian Sea pollutions when tropospheric aerosol heating is noted. c) An important related feature is a compensating downward lobe with a divergent inflow center over the Bay of Bengal. d) The presence of this downward lobe over the Bay of Bengal shows a reduction of winter monsoon rains over the south-east coast of India. e) We also show observational evidence of reduced winter monsoon rains over the south-east coast of India during MODIS pollution events from raingauge based estimates.