PNNL

Abstract

The net radiative effects of tropical clouds are determined by the evolution of thick, freshly detrained anvil clouds into thin anvil clouds. Thick anvil clouds reduce Earth's energy balance and cool the climate, while thin anvil clouds warm the climate. To determine role of these clouds in climate change we need to understand how interactions of their micro- and macrophysical properties control their radiative properties. We explore anvil cloud evolution using a cloud resolving model in three simulation setups of increasing complexity to disentangle the impacts of the various components of diabatic heating and their interaction with cloud-scale motions.The first phase of evolution and rapid cloud spreading is dominated by latent heating within convective updrafts. After the convective detrainment stops, most of the spreading and thinning of the anvil cloud is driven by cloud radiative processes and latent heating. The combination of radiative cooling at cloud top, latent cooling due to sublimation at cloud base, latent heating due to deposition and radiative heating in between leads to a sandwich-like, cooling-heating-cooling structure. The heating sandwich promotes the development of two within-anvil convective layers and a double cell circulation, dominated by strong outflow at 12 km altitude with in flow above and below. Our study reveals how small-scale processes including convective, microphysical processes, latent and radiative heating interact within the anvil cloud system. The absence or a different representation of only one component results in a significantly different cloud evolution with large impacts on cloud radiative effects.