Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 6 2009 10.5194/acpd-9-26029-2009 http://www.atmos-chem-phys-discuss.net/9/26029/2009/ http://www.atmos-chem-phys-discuss.net/9/26029/2009/acpd-9-26029-2009.html http://www.atmos-chem-phys-discuss.net/9/26029/2009/acpd-9-26029-2009.pdf 26029 26062 2009-12-07 Marine boundary layer over the subtropical southeast Pacific during VOCALS-REx – Part 1: Mean structure and diurnal cycle D. A. Rahn darahn@gmail.com R. D. Garreaud Departamento de Geofísica, Universidad de Chile, Santiago, Chile Atmospheric subsidence over the subtropical southeast Pacific (SEP) leads to a low-level anticyclonic circulation, a cool sea surface and a cloud-topped marine boundary layer (MBL). Observations in this region from a major field campaign during October and November 2008, the VOCALS Regional Experiment, provide ample data to characterize the lower atmospheric features over the SEP. The observations are also useful to test the ability of an area-limited, high-resolution atmospheric model to simulate the SEP conditions. Observations and model-results (where appropriate) improve the characterization of the mean state (Part 1) and variability (Part 2) of the lower troposphere including circulation, MBL characteristics and the upsidence wave. <br><br> Along 20&deg; S the MBL is generally deeper offshore (1600 m at 85&deg; W) but there is also considerable variability. MBL depth and variability decrease towards the coast and maximum inversion strength is detected between 74–76&deg; W. Southeasterly trades prevail within the MBL although the wind speed decreases toward the coast. Above the MBL along the coast of Chile, flow is northerly, has a maximum at 3 km, and extends westward to ~74&deg; W, apparently due to the mechanical blocking exerted by the Andes upon the westerly flow aloft. 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