Modeling of aerosol induced snow albedo feedbacks over the Himalayas and its implications on regional climate

Abstract

Regional climate model (RegCM-4.6.0) coupled with Community Land Model (CLM4.5), which includes SNow, ICe and Aerosol Radiation (SNICAR) model was used to investigate the effect of aerosol-induced snow albedo feedback on the regional radiation balance and atmospheric thermodynamics. During pre-monsoon (March–April–May) season, the deposition of absorbing aerosols such as dust and Black Carbon (BC) decreases the snow albedo of Himalayan–Tibetan region by 0.15 ± 0.13 causing a positive radiative effect of 14 ± 13 W m−2. In spite of the low absorption efficiency, the contribution of dust to the total radiative effect is found to be comparable to that due to BC over this region. The snow darkening due to aerosols increases the surface temperature by 1.33 ± 1.2 K, which results in the reduction of snow cover fraction by 7 ± 11%. The snow cover reduction is more than 20% in the mid-Himalayan region and northern Tibetan slopes due to its proximity to the major source regions like Indo-Gangetic Plain and Taklimakan desert respectively. Direct radiative effect (DRE, scattering and absorption of radiation) of atmospheric aerosols is smaller compared to the snow albedo effect (SAE) over the Himalayan region. DRE increase the mid-tropospheric temperature up to 1 K, whereas SAE effects are smaller and highly localized over the Himalayan region. Due to the large geographical extend of the forcing, the change in precipitation due to the direct effect is more prominent than that of the snow albedo effect. In general, change in snow cover fraction is dominated by the SAE and precipitation is more dominated by DRE. Present work demonstrates that the snow albedo feedback process over the Himalayan–Tibetan region plays a significant role in the regional climate of South Asia and therefore is crucial for the assessment of anthropogenic impacts.