92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Tuesday, 24 January 2012: 9:15 AM
The Impact of Aerosols on Fog Formation and Energy Budget in the California Central Valley
Room 244 (New Orleans Convention Center )
Hsiang-He Lee, University of California, Davis, CA; and S. H. Chen, M. J. Kleeman, and S. DeNero

The cooler temperatures and reduced sunlight of Central California's winter months make Tule Fog vanish slowly. This valley fog can persist for days and is a major safety concern for California motorists. Aerosol particles emitted in California's air basins can serve as cloud condensation nuclei (CCN). Furthermore, the aerosol number concentration, size, and composition can alter fog formation and the radiative budget. The primary goal of this research is to implement a source-oriented CCN module in the Weather Research and Forecasting model (WRF-Chem) to investigate the effects of aerosols from various sources on fog formations and their optical properties. Two fog events on February 21, 2007 and January 17, 2011 are used to demonstrate this module's capabilities. A new functionality to provide source-orientation for particulate matter (PM) operations has been developed within the WRF-Chem framework (SO-WRF-CHEM6D) by Prof. Kleeman's group at UC Davis. The SO-WRF-CHEM6D model tracks 6-dimensional chemical variables (X, Z, Y, Size Bins, Source Types, Species). Particle radius and number concentration are calculated explicitly for each source and bin. The initial tests use 25 chemical species from 5 emissions sources (dust, gasoline, diesel, meat cooking, and others) and 8 size bins, spanning range from 0.01 to 10 microns. We are now developing a new source-oriented CCN (activated PM) variable in SO-WRF-CHEM6D. The new model also includes the cloud feedbacks (e.g. wet scavenging) on aerosol distribution and number concentration. To understand the influence of aerosol particles serving as CCN in clean and polluted environments on the fog formation and radiation budget, five experiments will be conducted for each event. The SO-WRF-CHEM6D model will be integrated for 7-10 days, depending on the duration of the event. In all experiments, the two-moment Purdue Lin microphysics scheme will be used. Aerosol direct and indirect effects will be studied in these numerical experiments. Comparison among these experiments will help us understand the impact of aerosol-cloud-radiation effects on the energy and moisture budget, boundary layer instability, fog lifetime, fog thickness, etc.

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