VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study) is an international program that coordinates scientific activities to improve our understanding of the coupled ocean-atmosphere-land system over the southeastern Pacific Ocean. As part of VOCALS, a field campaign to be conducted in November 2008 will obtain a combination of in-situ and remotely sensed aerosol and cloud measurements. There are large point sources of sulfur dioxide and other particulate precursors along the coast of Chile and Peru contribute to particulates that can significantly affect the development of stratocumulus clouds far from the coast. Aircraft and ship missions will focus on understanding the processes that control precipitation, including the role of atmospheric aerosols, their transport from the land to the ocean, and their depletion by clouds.

The primary scientific question we plan to address is: What are the effects of aerosol chemistry on the evolution of CCN and stratocumulus clouds downwind of large anthropogenic point sources along the Pacific coast of Chile? In preparation for the VOCALS field campaign, we have employed the WRF-chem model to simulate the conditions during October 2006 to examine how well it simulates marine stratus, identify the horizontal transport pathways and vertical mixing of natural and anthropogenic aerosol precursors, and quantify the effects of simulated aerosol chemistry on the evolution of CCN and stratocumulus clouds. Our presentation will focus on quantifying how stratocumulus clouds affect particulate properties and determining to what extent particulates affect the amount, liquid water path, and albedo of stratocumulus clouds. Model performance will be assessed primarily with aerosol optical depth, droplet effective radius, and liquid water path data obtained from satellites. The simulations were also provided to the VOCALS model assessment that is critically assessing the ability of several regional and global models to simulate synoptically-varying clouds, meteorology, ocean circulation, and aerosols over the southeastern Pacific Ocean. Changes in our the modeling strategy for the VOCALS field campaign period will be discussed in terms of the in-situ cloud and aerosol property measurements made during November 2008.