ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-19581-2011 Aircraft millimeter-wave retrievals of cloud liquid water path during VOCALS-REx Zuidema P. 1 Leon D. 2 Pazmany A. 3 Cadeddu M. 4 Rosenstiel School of Marine and Atmospheric Sciences, Univ. of Miami, Miami, Florida, USA Department of Atmospheric Sciences, University of Wyoming, Laramie, Wyoming, USA Prosensing Inc., Amherst, Massachusetts, USA Argonne National Laboratory, Argonne, Illinois, USA 08 07 2011 11 7 19581 19616 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-discuss.net/11/19581/2011/acpd-11-19581-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/19581/2011/acpd-11-19581-2011.pdf

A unique feature of the VOCALS Regional Experiment was the inclusion of a small, inexpensive, zenith-pointing millimeter-wavelength passive radiometer on the fourteen research flights of the NCAR C-130 plane, the G-band (183 GHz) Vapor Radiometer (GVR). The radiometer permitted above-cloud retrievals of water vapor path, and cloud liquid water path retrievals at 1 Hz resolution for the sub-cloud and cloudbase aircraft legs when combined with in-situ thermodynamic data. Retrieved free-tropospheric (above-cloud) water vapor paths possessed a strong longitudinal gradient, with off-shore values of one to two mm and near-coastal values reaching one cm. Overall the free-troposphere was drier than that sampled by radiosondes in previous years. For the sub-cloud legs, the absolute (between-leg) and relative (within-leg) LWP accuracy was estimated at 20–25 and 5 g m<sup>−2</sup> respectively for well-mixed conditions, with greater uncertainties expected for decoupled conditions. Clouds with retrieved liquid water paths between 200 to 400 g m<sup>−2</sup> matched adiabatic values derived from coincident cloud thickness measurements exceedingly well. A significant contribution of the GVR dataset is the extended information on the thin clouds, with 66 % of the retrieved LWPs < 100 g m<sup>−2</sup>. Nevertheless, the overall LWP cloud fraction of 62 % was less than the 92 % cloud cover determined by airborne cloud lidar and radar combined.

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