Impact of Arabian Sea pollution 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 modeling the impacts of pollution. We use a NASA Goddard Earth Observing System (GEOS) model to carry out many comparative forecast simulation experiments that include the pollution based on MODIS and control runs that utilize climatological estimates of pollutions. The model invokes both the direct and indirect effects of aerosols. Our observations are as follows: (1) The Arabian Sea experienced above normal rain during these periods for the MODIS experiments as compared to the control. (2) The most interesting feature is the divergent outflow center, in the upper troposphere, over polluted regions of the atmosphere over the Arabian Sea as a consequence of tropospheric aerosol heating. (3) An important related feature is a compensating downward lobe with a divergent inflow in the upper troposphere center over the Bay of Bengal. (4) The presence of this downward lobe over the Bay of Bengal relates to a reduction of winter monsoon rains over the southeast coast of India. (5) We also show evidence of similarly reduced winter monsoon rains in raingauge data over the southeast coast of India during high‐pollution events ascertained from MODIS data.