Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 10 8 2010 10.5194/acpd-10-18419-2010 http://www.atmos-chem-phys-discuss.net/10/18419/2010/ http://www.atmos-chem-phys-discuss.net/10/18419/2010/acpd-10-18419-2010.html http://www.atmos-chem-phys-discuss.net/10/18419/2010/acpd-10-18419-2010.pdf 18419 18466 2010-08-04 A regional real-time forecast of marine boundary layers during VOCALS-Rex S. Wang shouping.wang@nrlmry.navy.mil L. W. O'Neill Q. Jiang S. P. de Szoeke X. Hong H. Jin W. T. Thompson X. Zheng Naval Research Laboratory, Monterey, CA, USA National Research Council, Naval Research Laboratory, Monterey, CA, USA University Corporation for Atmospheric Research, Monterey, CA, USA Oregon State University, College of Ocean and Atmospheric Sciences, Corvallis, Oregon, USA RSMA, University of Miami, Miami, FL, USA This paper presents an evaluation and validation of the Naval Research Laboratory's COAMPS real-time forecasts during the VOCALS-Rex over the area off the west coast of Chile/Peru in the Southeast Pacific during October and November 2008. The analyses focus on the marine boundary layer (MBL) structure. These forecasts are compared with lower troposphere soundings, surface measurements, and satellite observations. The predicted mean MBL cloud and surface wind spatial distributions are in good agreement with the satellite observations. The large-scale longitudinal variation of the MBL structure along 20° S is captured by the forecasts. That is, the MBL heights increase toward the open ocean, the moisture just above the inversion decreases, and the MBL structure becomes more decoupled offshore. The observed strong wind shear across the cloud-top inversion in coastal area at 20° S was correctly predicted by the model. Our results show that the sporadic cloud spatial and temporal distribution in the 15 km grid mesh is caused by grid-scale convection likely due to a lack of a shallow cumulus convection parameterization in the model. Both observations and model forecasts show wind speed maxima near the top of MBL along 20° S, which is consistent with the west-ward upslope of the MBL heights based on the thermal wind relationship. The forecasts produced well-defined diurnal variations in the spatially averaged MBL structure, although the overall signal is weaker than those derived from the in situ measurements and satellite data. The MBL heights are generally underpredicted in the nearshore area. 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