Inclusion of Ammonium Sulfate Aerosols in McRAS-AC: an SCM Evaluation

Partha Bhattacharjee George Mason University
Lazaros Oreopoulos NASA
Yogesh Sud NASA - Goddard Space Flight Center
Jun Wang University of Nebraska, Lincoln
Ruixing Yang George Mason University

Category: Aerosol-Cloud-Radiation Interactions

Working Group: Cloud-Aerosol-Precipitation Interaction

Simulated ice clouds have large biases in present-day climate models, particularly GCMs that include aerosol-cloud interactions for nucleating cloud particles. Major gaps in our understanding of ice and mixed-phase clouds emanate from a lack of sufficient observations to better parameterize or evaluate them. Recent observational studies have led to the discovery of significant nucleating effects of ammonium sulfate (NH4)2SO4 aerosols found in the upper troposphere that were not included in the cloud physics of McRAS-AC, NASA’s microphysical cloud scheme with Relaxed Arakawa Schubert cloud parameterization upgraded with aerosol-cloud interactions physics. Therefore, McRAS-AC was modified to invoke a realistic parameterization of (NH4)2SO4 aerosols and then used to evaluate its impact on clouds using a single-column model (SCM) employing the Southern Great Plains (SGP) and North Slope of Alaska (NSA) driver data sets. Twin simulations with and without (NH4)2SO4 aerosols were produced. The statistical behavior of the simulated clouds was evaluated against the available ground and satellite data to determine the influence of (NH4)2SO4 aerosols on cloud particle number densities, size, optical thicknesses, and the resulting long- and short-wave cloud radiative forcings. The results show that inclusion of (NH4)2SO4 in the SCM mitigates some major biases in the simulated ice clouds while preserving the reasonable McRAS-AC simulation of liquid clouds. The detailed results of our poster will make a strong case for including (NH4)2SO4 aerosols not only in McRAS-AC, but in all interactive aerosol-cloud schemes.

This poster will be displayed at ASR Science Team Meeting.

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