A Multimodel Assessment of Aerosol Impacts on Deep Convective Cloud Systems

Aerosol impacts on the properties, processes and lifetimes of clouds continues to be one of the largest uncertainties in our understanding and ability to simulate the Earth's climate system. One of the primary goals of the Aerosol, Cloud, Precipitation, and Climate (ACPC) working group (www.acpcinitiative.org) is to assist in reducing this uncertainty, thereby enhancing our understanding of aerosol-cloud interactions. The ACPC working group recently organized an intermodel comparison study in which the impacts of aerosols on the properties of deep convective clouds have been examined. Seven different state-of-the-art cloud-resolving model frameworks, with varying aerosol and microphysical parameterizations, were used to simulate a Houston, TX, case study of the development of isolated convection under a wide range of observationally-based aerosol conditions.

In this talk we will present the results from this intermodal comparison, with a focus on aerosol impacts on both the microphysical and dynamical properties of the simulated convective clouds, including cloud droplet and rain drop characteristics, surface precipitation rates, updraft and downdraft attributes, and cold pool development. The model results will also be compared with the observational data from this case study wherever possible. As a large number of isolated convective updrafts were observed to occur during the case study time period, a novel tracking algorithm was developed in order to fully track the evolution of these updrafts, thereby allowing us to obtain meaningful statistics of aerosol impacts on convection. The range of model responses to the varying aerosol concentrations will be presented, with a specific focus on both the similarities and differences between the model solutions, and the reasons for these.