Rethinking the connection between aerosols, meteorology, and snowmelt patterns in High Mountain Asia: Using a novel regional reanalysis

Snowmelt in Third Pole regions like High Mountain Asia (HMA) results from meteorological forcing and their complex interactions with light-absorbing particles (LAPs) originating from remote and nearby pollution sources. However, the impact of these aerosol-meteorology interactions (AMI) on snow remains ambiguous in the context of a changing climate and Earth System Models (ESMs). In this study, we substantiate the importance of AMI in driving snow cover fraction (SCF) variations in low snow-covered glacial regions during the late snowmelt season (May-July). We put forward a combination of statistical multi-linear regression and explainable machine learning approaches on three major reanalyses and satellite observations. In addition to the reanalyses from ECMWF (ERA-5/CAMS) and NASA GMAO (MERRA-2), we utilize a regional chemical reanalysis MATCHA (Model for Atmospheric Transport and Chemistry in Asia) developed by NCAR to analyze these interactions. Our findings reveal that AMI accounts for approximately 20% of SCF variability, with atmospheric carbonaceous aerosols and synoptic circulation being key contributors. We highlight the differences in the representation of AMI across the three reanalyses, with promising results from MATCHA, a more refined and fully coupled reanalysis that captures observable AMI. The MATCHA reanalysis presents a viable alternative for studying the HMA cryosphere because it incorporates the coupling between aerosols, snow, and radiation, as well as daily assimilation of satellite AOD and total column CO. Insights from this study underscore the need to 1) advance functional representations of AMI through improved coupling parameterizations in current climate models and 2) incorporate the afore-mentioned geophysical quantities in the design and development of observing systems and ESMs. Accounting for interactions like AMI in ESMs can improve medium-range forecasts of high-impact weather, particularly hydrological extremes in freshwater-vulnerable regions like HMA.