Aerosol processes perturb cloud trends over Bay of Bengal: observational evidence

Abstract

Abstract Although, the aerosol-cloud interactions and its impact on daily to seasonal radiation/temperature has been well observed over South Asia in last two decade, the role of aerosol-cloud interactions on cloud occurrence trends (and surface temperature) is yet not evident. Here, evidence of aerosol-induced control on cloud occurrence trends over the Northern Bay of Bengal (NBOB) during the monsoon onset period is presented. In last 15 years, increased aerosol emissions over North India have led to an increase in aerosol loading at an elevated altitude of 1–3 km over the NBOB outflow region in monsoon onset period. This elevated aerosol loading induces increases the air temperature at 1–2 km altitude and stabilizes the lower troposphere over the region in recent years. The enhanced atmospheric stability in the region caused low-level cloud occurrences (below 3 km) to increase in recent years by ~20%, potentially contributing to the observed non-intuitive cooling trends in sea surface temperatures. These aerosol-cloud-climate observations emphasize the crucial need for improved aerosol representations in coupled ocean-atmosphere models for accurate predictions of climate change over South Asia.