Use of Observation-Based Aerosol Fields for Detailed Cloud-Scale Modeling Studies

Abstract:

Within the realm of detailed large-eddy simulation studies with size-resolved microphysics, substantial uncertainties exist regarding the ability of any given model to accurately reproduce basic aspects of cloud microphysics that interact with ambient aerosol properties, such as precipitation formation and evolution. Modeling studies intended to reproduce specific observed cloud fields must also to some degree simplify the complexity of aerosol conditions, and usually lack sufficient measurements to well constrain the most relevant aerosol properties. Here we describe derivation and use of spatiotemporally varying fields of multi-modal aerosol size distributions for 60-hour simulations of boundary-layer clouds observed over Oklahoma during the RACORO campaign. Cases include forced as well as freely convecting shallow clouds, and some warm precipitation. We investigate the sensitivity of simulations to observation-derived aerosol inputs, including hygroscopicity parameter and size distribution properties. Sensitivity is examined in the context of the ability of the simulations to accurately reproduce relevant macrophysical and microphysical cloud properties observed, including droplet size dispersion.