Analysis of synoptic weather and atmospheric conditions associated with aerosol episodes over Indo-Gangetic Plains, India

The present study aims at identifying episodes of high aerosol loading and analyzes the synoptic and weather conditions favoring the occurrence of heavy aerosol-laden atmosphere over the Indo-Gangetic Plains (IGP), India during the last decade (2001-2010). The data from the Kanpur AERONET station located in the central part of IGP are used to identify aerosol episodes with daily-mean aerosol optical depth (AOD) above the decadal mean + 1 standard deviation, while the threshold value is defined to 0.928. For examining the synoptic and weather conditions, mean sea level pressure (MSLP) and geopotential height at 700 hPa obtained from the NCEP/NCAR Reanalysis Project are used. The analysis identifies 277 aerosol episodes over Kanpur corresponding to 13.2% of the available dataset. These are most frequently observed during post-monsoon (18.6%) and monsoon (14.7%) seasons associated with the transport of anthropogenic emissions from fossil-fuel, biofuel and crop-residue burning episodes as well as intrusion of desert dust, respectively. During post-monsoon and winter seasons, the aerosol episodes are associated with enhanced presence of fine-mode aerosols from anthropogenic pollution and biomass burning, while in pre-monsoon and monsoon seasons they are mostly associated with desert-dust occurrence. The multivariate statistical methods Factor Analysis and Cluster Analysis are applied on the 277 700 hPa patterns over south Asia in order to group them objectively into representative types. Six clusters of 700 hPa synoptic patterns (episode days) are found and for each of them the mean climatology over south Asia for MSLP is also examined in order to reveal its influence on the accumulation of aerosols over IGP. Furthermore, the spatial distribution of aerosols obtained from Terra-MODIS is examined over Indian sub-continent and IGP in order to identify aerosol hot-spot areas for each cluster of weather. Results from this study are expected to help better understand the strong variations in aerosol loading over the IGP associated with meteorological anomalies as well as due to regional transport/emission processes.