Title: Aircraft millimeter-wave passive sensing of cloud liquid water and water vapor during VOCALS-REx

Abstract

Routine liquid water path measurements and water vapor path are valuable for process studies of the cloudy marine boundary layer and for the assessment of large-scale models. The VOCALS Regional Experiment respected this goal by including a small, inexpensive, upwardpointing millimeter-wavelength passive radiometer on the fourteen research flights of the NCAR C-130 plane, the Gband (183 GHz) Vapor Radiometer (GVR). The radiometer permitted above-cloud retrievals of the free-tropospheric water vapor path (WVP). Retrieved free-tropospheric (abovecloud) water vapor paths possessed a strong longitudinal gradient, with off-shore values of one to twomm and nearcoastal values reaching tenmm. The VOCALS-REx free troposphere was drier than that of previous years. Cloud liquid water paths (LWPs) were retrieved from the sub-cloud and cloudbase aircraft legs through a combination of the GVR, remotely-sensed cloud boundary information, and insitu thermodynamic data. The absolute (between-leg) and relative (within-leg) accuracy of the LWP retrievals at 1 Hz (≈100 m) resolution was estimated at 20 gm^-2 and 3 gm^-2 respectively for well-mixed conditions, and 25 gm^-2 absolute uncertainty for decoupled conditions where the input WVP specification was more uncertain. Retrieved liquid water paths matched adiabatic values derived from coincident cloud thickness measurements exceedingly well. A significant contribution of the GVRmore » dataset was the extended information on the thin clouds, with 62% (28 %) of the retrieved LWPs <100 (40) gm^-2. Coastal LWPs values were lower than those offshore. For the four dedicated 20° S flights, the mean (median) coastal LWP was 67 (61) gm^-2, increasing to 166 (120) gm^-2 1500 km offshore. Finally, the overall LWP cloud fraction from thirteen research flights was 63 %, higher than that of adiabatic LWPs at 40 %, but lower than the lidar-determined cloud cover of 85 %, further testifying to the frequent occurrence of thin clouds.« less

Authors:

Zuidema, P. ^[1]; Leon, D. ^[2]; Pazmany, A. ^[3]; Cadeddu, M. ^[4]

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+ Show Author Affiliations

1. Univ. of Miami, Miami, FL (United States). Rosenstiel School of Marine and Atmospheric Sciences
2. Univ. of Wyoming, Laramie, WY (United States). Dept. of Atmospheric Sciences
3. Prosensing Inc., Amherst, MA (United States)
4. Argonne National Lab. (ANL), Argonne, IL (United States)

Publication Date:

Thu Jan 05 00:00:00 EST 2012

Research Org.:

Argonne National Laboratory (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF)

OSTI Identifier:

1396248

Grant/Contract Number:  

AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Atmospheric Chemistry and Physics (Online)

Additional Journal Information:

Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 12; Journal Issue: 1; Journal ID: ISSN 1680-7324

Publisher:

European Geosciences Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES