The Life Cycle of TTL Cirrus: A Model Evaluation using the DYAMOND Simulations

Abstract

Thin cirrus in the tropics are important for climate because of their warming effect on the atmosphere and large spatiotemporal extent, coinciding with locations of deep convection. Tropical cirrus are difficult to observe due to their high altitude and thin optical depths. They are also difficult to simulate in conventional global climate models because of the coarse grid spacing and simplified parameterizations of deep convection and cirrus formation in such models. We investigate the representation of tropical cirrus in global storm-resolving models (GSRMs) because they have higher spatiotemporal resolution and explicit convection, which could provide a more accurate representation of cloud processes. This study uses GSRMs from the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) project. The aggregate life cycle of topical cirrus are analyzed using joint albedo-OLR histograms to determine the fidelity of models in capturing the observed distribution of cloud populations over representative tropical ocean and land regions. Some models generate more optically thick cirrus or anvils while thin cirrus dominate in other models. Model differences, likely driven by sub-grid processes such as ice microphysics, dominate over the more subtle regional shifts. Understanding the differences in the GSRMs is an important step toward reducing uncertainty in predictions of future warming that is generated by high cloud feedbacks.