Radiative sensitivities of tropical anvils to small ice crystals

Abstract

Cloud evolution was modeled in a one-dimensional (vertical) framework incorporating an updraft, deposition, sublimation, sedimentation, nucleation, and radiation. The shortwave forcing and albedo were very sensitive to the presence of the small crystals (3 <2% of total cloud mass. For optically thick anvils the longwave forcing and emissivity were, in general, much less sensitive to the small ice crystals than their shortwave counterparts. Radiative treatments assuming a hexagonal crystal habit yielded the same sensitivities as the spherical habit. The increased backscatter from hexagonal crystals enhanced the planetary albedo by ~10-15%. The heating rate sensitivity to the small crystals depended on vertical location within the cloud and showed cancelation between the longwave and the shortwave heating perturbations. The small crystals changed heating rates by up to 50% at cloud top and base. -from Authors