Impact of Anthropogenic Aerosol on the Properties of Shallow Maritime Cumulus Clouds

Abstract:

The northern Indian Ocean region is frequently covered by cumulus clouds that are responsible for moistening the boundary layer and contribute to tropical deep convection. Because this region is uniquely located close to the highly polluted Indian plateau, air mass with high aerosol concentration can be easily transported to this area. These small cumulus clouds, coupled with the effects of aerosol, have a large potential to affect the regional and global albedo. The aerosol effects on cloud properties and atmospheric structures are examined in this work, using the UAV (Unmanned Aerial Vehicle) data that are observed from CARDEX (Cloud, Aerosol, Radiative forcing, Dynamics EXperiment) and MAC (Maldives Autonomous unmanned aerial vehicle Campaign). On average, the high polluted cases show warmer temperature through the entire atmospheric column and higher relative humidity in boundary layer. The maximum temperature difference between high and low polluted cases can be found around the cloud layer altitude. In addition, the height of sub-cloud mixed layer is higher in low polluted cases. Clouds in high polluted cases are generally becoming narrower and taller than those in low polluted cases, and are associated with greater cloud water content and higher cloud droplet number concentrations, especially in small droplet range (diameters less than 10 micrometers). Meanwhile, the effective radius of cloud droplets decreases as the aerosol concentration increases. These facts indicate that the high polluted clouds are on average brighter with higher albedo.