The PreVOCA experiment: modeling the lower troposphere in the Southeast Pacific
- ISSN: 1680-7324
- DOI: 10.5194/acpd-9-23909-2009
The Preliminary VOCALS Model Assessment (PreVOCA) aims to assess\ncontemporary atmospheric modeling of the subtropical South East Pacific,\nwith a particular focus on the clouds and the marine boundary layer\n(MBL). Models results from fourteen modeling centers were collected\nincluding operational forecast models, regional models, and global\nclimate models for the month of October 2006. Forecast models and global\nclimate models produced daily forecasts, while most regional models were\nrun continuously during the study period, initialized and forced at the\nboundaries with global model analyses. Results are compared in the\nregion from 40 degrees S to the equator and from 110 degrees W to 70\ndegrees W, corresponding to the Pacific coast of South America.\nMean-monthly model surface winds agree well with QuikSCAT observed winds\nand models agree fairly well on mean weak large-scale subsidence in the\nregion next to the coast. However they have greatly differing geographic\npatterns of mean cloud fraction with only a few models agreeing well\nwith MODIS observations. Most models also underestimate the MBL depth by\nseveral hundred meters in the eastern part of the study region. The\ndiurnal cycle of liquid water path is underestimated by most models at\nthe 85 degrees W 20 degrees S stratus buoy site compared with satellite,\nconsistent with previous modeling studies. The low cloud fraction is\nalso underestimated during all parts of the diurnal cycle compared to\nsurface-based climatologies. Most models qualitatively capture the MBL\ndeepening around 15 October 2006 at the stratus buoy, associated with\ncolder air at 700 hPa.