Influence of aerosols on clouds, precipitation and freezing level height over the foothills of the Himalayas during the Indian summer monsoon

摘要

Long term (2002-2017) satellite-retrieved and reanalysis datasets are utilized to assess the daily and interannual timescale impact of aerosol loadings on the cloud properties, precipitation amounts, and freezing level height over the southern slopes and adjacent foothills (SSFH) of the Himalayas during the Indian summer monsoon season. Daily timescale composites during polluted days suggest the development of widespread deeper clouds and higher precipitation amounts. Significant efforts were carried out to isolate the role of weather forcing in the daily timescale from the outlined aerosol-cloud-precipitation relationship by using the environmental relative humidity (RH) and vertical velocity (omega). Results provide strong evidence suggesting that regardless of weather pattern forcing, the direct association of aerosol optical depth (AOD) with precipitation, and cloud properties remained consistent for day-to-day timescales. The spatial correlation analyses of daily AOD with cloud properties and precipitation during both wet and dry monsoonal years indicate a positive association of higher aerosol concentration with cloud vertical development and precipitation. The 0 degrees C isotherm altitude is found to be higher by 136.82 +/- 18.82 m (mean +/- standard deviation) during the polluted days in comparison to relatively cleaner environments, which can be crucial for the change in snow line and melting of glaciers impacting the hydroclimate of the Himalayas. Our results suggest that the influence of aerosol on modulating the regional precipitation and freezing level height can be significant for the hydroclimate of the Himalayan region in a daily to interannual timescale.