Aerosol-cloud-interactions (aci) in continental warm clouds over India

Impacts of aerosols on warm clouds have contributed to significant uncertainty in radiative forcing estimates and climate predictions, as warm clouds reflect much of the incoming solar radiation. The variables which influence cloud reflectivity, or albedo, over continental land regions are cloud droplet effective radius, cloud liquid water content, and cloud fraction. In this study, we investigate factors impacting aerosol cloud-mediated changes in cloud effective radius (Twomey effect or first indirect effect) over the Indian region using satellite-mounted radiometer and LIDAR data. Datasets from 2002-2018 include daily observational gridded data (Level 3, 1°*1°, MYD08_D3) for aerosol and cloud variables from MODIS Aqua collection 6.1, along with meteorological variables from ERA-Interim reanalysis and aerosol type from CALIOP level-2 aerosol layer product for 2007-2018. The land areas show a distinct increase in cloud effective radius in response to increased pollution load, exhibiting an "anti-Twomey" effect, with the potential to offset cloud radiative cooling. This observed behavior is preserved spatially, across observation years and clouds of differing vertical extent. This behavior is not governed by cloud liquid water path (LWP) but is exhibited across its entire range including convective cores. Convective cores (90th percentile LWP) in warm clouds are analyzed owing to their adiabatic vertical profile and over the land regions show an anti-Twomey effect. Stronger stability and larger inversion over land regions indicate a smaller radius, including evaporation-entrainment feedback.

Figure: (top) Dependence of cloud droplet effective radius on aerosol. (middle) Aerosol cloud interaction (ACI) metric for land and ocean decomposed. (bottom) Lower troposphere stability and aerosol type for the Indian region is shown.