The role of meteorology in the accumulation of aerosols over Ganges Basin: Climate implications during severe aerosol episodes

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Kaskaoutis D.G., Houssos E.E., Sinha P.R., Nastos P.T., Bartzokas A., Gautam RKosmopoulos., P.G., Kharol S.K. and Singh R.P. (2013)
Workshop on AtmosphericComposion and the Asian Summer Monsoon, Kathmadu, Nepal, June 2013


It is widely known that regional meteorology and monsoon system strongly influence the atmospheric dynamics, aerosol field and climate implications over south Asia. The present work investigates the synoptic weather and atmospheric conditions favoring the accumulation of aerosols over Ganges Basin during the period 2001-2010. Based on AERONET data series over Kanpur 277 days are characterized as aerosol episodes days (AEDs), associated with daily-mean aerosol optical depth (AOD500) above the decadal (2001-10) mean + 1STDEV (AOD500>0.928). The majority of the AEDs is found in the post-monsoon season corresponding to the 18.6% of the available dataset in this season, while the fractions are 12.5%, 9.1% and 14.7% for winter, pre-monsoon and monsoon, respectively. It is also found that the AEDs in post-monsoon and winter are dominated by enhanced presence of fine-mode aerosols from fossil fuel and biofuel combustions as well as crop residue burning. In contrast, the severe AODs during pre-monsoon and monsoon are associated with increasing desert dust aerosols originated from Thar Desert or long-range transported from Arabian Peninsula and Middle East. For the classification of the synoptic weather conditions associated with AEDs over Ganges Basin, mean sea level pressure (MSLP) and geopotential height at 700 hPa (Z700) data, obtained from the NCEP/NCAR Reanalysis Project, are used. By means of the multivariate statistical methods Factor Analysis and Cluster Analysis applied on the Z700 patterns, six clusters of Z700 circulation patterns are identified and for each of them the composite mean for MSLP and Z700 as well as their anomalies from the mean climatology during the period 1981-2010 are studied. It is found that the accumulation of aerosols over Ganges Basin for specific weather clusters occurring in late pre-monsoon and monsoon can be explained by synoptic meteorology and the anomalies from the mean climatology that favoring drought conditions, increasing dust activity and longer aerosol lifetime. The Aerosol Radiative Forcing (ARF) at surface is found to be extremely large (~-150 to -170 Wm-2) for the AEDs on seasonal basis also associated with high atmospheric heating (~110-150 Wm-2). It is seen that the high aerosol loading during these days may cause severe climate implications over Ganges Basin with further consequences on atmospheric heating, cloud microphysics, monsoon rainfall and melting of Himalayan glaciers. Results from this study are expected to help better understand the strong variations in aerosol loading over Ganges Basin associated with meteorological anomalies as well as due to regional transport/emission processes.