730 Sensitivity of Aerosol-Meteorology Feedbacks in Convection-Permitting WRF/Chem Simulations to the Height of Idealized External Pollution Plumes

Wednesday, 26 January 2011
4E (Washington State Convention Center)
Zhan Zhao, SIO/Univ. Of California, La Jolla, CA; and L. M. Russell and M. S. Pritchard

Modern global climate models (GCMs) admit explicit aerosols that can be applied as boundary conditions to high-resolution chemistry-enabled regional climate models (RCMs) to investigate projected aerosol forcing on regional meteorology and air quality. It is unknown to what extent imperfect GCM vertical plume structures (slave to convection parameterization) will translate into errors in RCMs driven in this manner: How sensitive are chemistry enabled RCMs to the vertical positioning of external pollution plumes impinging on their outermost boundaries when domain nesting is involved?

Both the aerosol direct and indirect effects are included in Weather Research and Forecasting Model with Chemistry (WRF/Chem), providing an ideal testbed to explore the meteorological response to different aerosol scenarios at convective-permitting resolution. We apply WRF/Chem to investigate its meteorological response to external plumes injected on different elevations at the outermost upstream boundaries during a convective event in the eastern US with three nesting domains. By injecting plumes at different heights on the boundaries we isolate which of these pathways dominate at various heights, and investigate the overall altitude sensitivity of the RCM response. When injected within a specific zone of heights, the aerosols from the prescribed plumes have the capacity to influence the simulated convective system by altering cloud droplet numbers, cloud optical depth, precipitation efficiency of clouds, as well as accumulated precipitation through aerosol indirect effect. In turn, changes in the simulated convective system affect the aerosol concentration through in-cloud and below-cloud wet removal processes. In contrast, when the pathway of the plume is above the convective system, the aerosol radiative effect dominates, and the convective system is relatively insensitive to the prescribed plume.

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