PNNL

Abstract

The Preliminary VOCALS Model Assessment (PreVOCA) aims to assess contemporary atmospheric modeling of the subtropical South East Pacific, with a particular focus on the clouds and the marine boundary layer (MBL). Models results from fourteen modeling centers were collected including operational forecast models, regional models, and global climate models covering the month of October 2006. Forecast models and global climate models produced daily forecasts, while most regional models were run continuously during the study period, initialized and forced at the boundaries with global model analyses. Results are compared in the region from 40S to the equator and from 110W to 70W. Mean-monthly model surface winds agree well with QuikSCAT observed winds and models agree fairly well on mean weak large-scale subsidence in the region near the South American coast. However they have greatly differing mean geographic patterns of cloud fraction with only a few models agreeing well with MODIS observations. Most models also underestimate the boundary layer depth by several hundred meters in the eastern part of the study region. The modeled diurnal cycle of liquid water path is underestimated by most models at the 85W 20S stratus buoy compared with satellite, consistent with previous modeling studies. The low cloud fraction is also underestimated during all parts of the diurnal cycle compared with surface-based climatologies. Most models qualitatively capture the boundary layer deepening around 15 Oct 2006 at the stratus buoy, associated with colder air at 700hPa.