ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-9943-2011 Observations of the boundary layer, cloud, and aerosol variability in the southeast Pacific near-coastal marine stratocumulus during VOCALS-REx Zheng X. 1 Albrecht B. 1 Jonsson H. H. 2 Khelif D. 3 Feingold G. 4 Minnis P. 5 Ayers K. 5 Chuang P. 6 Donaher S. 1 Rossiter D. 6 Ghate V. 7 Ruiz-Plancarte J. 3 Sun-Mack S. 8 Division of Meteorology and Physical Oceanography, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA Naval Postgraduate School, Monterey, CA, USA University of California, Irvine, Irvine, CA, USA NOAA Earth System Research Laboratory (ESRL), Boulder, CO, USA NASA Langley Research Center, Hampton, USA University of California, Santa Cruz, Santa Cruz, CA, USA Rutgers University, New Brunswick, NJ, USA Science Systems and Applications, Inc., Hampton, VA, USA 27 09 2011 11 18 9943 9959 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/9943/2011/acp-11-9943-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/9943/2011/acp-11-9943-2011.pdf

Aircraft observations made off the coast of northern Chile in the Southeastern Pacific (20° S, 72° W; named Point Alpha) from 16 October to 13 November 2008 during the VAMOS Ocean-Cloud- Atmosphere-Land Study-Regional Experiment (VOCALS-REx), combined with meteorological reanalysis, satellite measurements, and radiosonde data, are used to investigate the boundary layer (BL) and aerosol-cloud-drizzle variations in this region. On days without predominately synoptic and meso-scale influences, the BL at Point Alpha was typical of a non-drizzling stratocumulus-topped BL. Entrainment rates calculated from the near cloud-top fluxes and turbulence in the BL at Point Alpha appeared to be weaker than those in the BL over the open ocean west of Point Alpha and the BL near the coast of the northeast Pacific. The cloud liquid water path (LWP) varied between 15 g m<sup>−2</sup> and 160 g m<sup>−2</sup>. The BL had a depth of 1140 ± 120 m, was generally well-mixed and capped by a sharp inversion without predominately synoptic and meso-scale influences. The wind direction generally switched from southerly within the BL to northerly above the inversion. On days when a synoptic system and related mesoscale costal circulations affected conditions at Point Alpha (29 October–4 November), a moist layer above the inversion moved over Point Alpha, and the total-water mixing ratio above the inversion was larger than that within the BL. The accumulation mode aerosol varied from 250 to 700 cm<sup>−3</sup> within the BL, and CCN at 0.2 % supersaturation within the BL ranged between 150 and 550 cm<sup>−3</sup>. The main aerosol source at Point Alpha was horizontal advection within the BL from south. The average cloud droplet number concentration ranged between 80 and 400 cm<sup>−3</sup>. While the mean LWP retrieved from GOES was in good agreement with the in situ measurements, the GOES-derived cloud droplet effective radius tended to be larger than that from the aircraft in situ observations near cloud top. The aerosol and cloud LWP relationship reveals that during the typical well-mixed BL days the cloud LWP increased with the CCN concentrations. On the other hand, meteorological factors and the decoupling processes have large influences on the cloud LWP variation as well.

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