AAAR 30th Annual Conference
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Daniel Westervelt

Evaluating the GEOS-Chem-TOMAS global aerosol microphysics model

DANIEL WESTERVELT, Tiana Warren, Peter Adams

Carnegie Mellon University

     Abstract Number: 73
     Last modified: March 29, 2011

     Working Group: Aerosols, Clouds, and Climate

Global aerosol microphysics models typically contain many uncertain parameters that necessitate evaluation and comparison against ambient measurement field campaigns. In this study, we make a detailed and thorough model evaluation of the Two-Moment Aerosol Sectional (TOMAS) microphysical algorithm hosted by the GEOS-Chem global chemical transport model. The focus of this comparison is on aerosol number concentrations and size distributions. We have compiled size distribution data that span various regions of the oceans and continents, including the extensive EUSAAR database. We also evaluate model predicted cloud condensation nuclei concentrations against measurements carried out with a variety of instruments at a variety of critical supersaturations. Finally, we use model output to reproduce an observed correlation between aerosol optical depth (AOD) and CCN. In order to test the model for seasonal variation, we compare output on a montly basis in addition to annual averages. Results show good agreement in size distributions at rural European sites and less agreement at polluted continental sites. Modeled aerosol number concentrations are at worst within a factor of 5 of the measurements at all sites. The aim of this project to evaluate the global aerosol microphysics model in a number of different ways will yield useful information about strengths and weaknesses of the GEOS-Chem-TOMAS model.

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