Comparison of water vapor measurements by airborne Sun photometer and near-coincident in situ and satellite sensors during INTEX/ITCT 2004

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Read Full Article (file size: 3306692 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D12S16, doi:10.1029/2006JD007733, 2007 Comparison of water vapor measurements by airborne Sun photometer and near-coincident in situ and satellite sensors during INTEX/ITCT 2004 J. Livingston SRI International, Menlo Park, California, USA B. Schmid Bay Area Environmental Research Institute, Sonoma, California, USA J. Redemann Bay Area Environmental Research Institute, Sonoma, California, USA P. B. Russell NASA Ames Research Center, Moffett Field, California, USA S. A. Ramirez Bay Area Environmental Research Institute, Sonoma, California, USA J. Eilers NASA Ames Research Center, Moffett Field, California, USA W. Gore NASA Ames Research Center, Moffett Field, California, USA S. Howard Bay Area Environmental Research Institute, Sonoma, California, USA J. Pommier Bay Area Environmental Research Institute, Sonoma, California, USA E. J. Fetzer Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA S. W. Seemann Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin, Madison, Wisconsin, USA E. Borbas Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin, Madison, Wisconsin, USA D. E. Wolfe Earth System Research Laboratory, NOAA, Boulder, Colorado, USA A. M. Thompson Meteorology Department, Pennsylvania State University, University Park, Pennsylvania, USA Abstract We have retrieved columnar water vapor (CWV) from measurements acquired by the 14-channel NASA Ames Airborne Tracking Sun photometer (AATS-14) during 19 Jetstream 31 (J31) flights over the Gulf of Maine in summer 2004 in support of the Intercontinental Chemical Transport Experiment (INTEX)/Intercontinental Transport and Chemical Transformation (ITCT) experiments. In this paper we compare AATS-14 water vapor retrievals during aircraft vertical profiles with measurements by an onboard Vaisala HMP243 humidity sensor and by ship radiosondes and with water vapor profiles retrieved from AIRS measurements during eight Aqua overpasses. We also compare AATS CWV and MODIS infrared CWV retrievals during five Aqua and five Terra overpasses. For 35 J31 vertical profiles, mean (bias) and RMS AATS-minus-Vaisala layer-integrated water vapor (LWV) differences are −7.1% and 8.8%, respectively. For 22 aircraft profiles within 1 hour and 130 km of radiosonde soundings, AATS-minus-sonde bias and RMS LWV differences are −5.4% and 10.7%, respectively, and corresponding J31 Vaisala-minus-sonde differences are 2.3% and 8.4%, respectively. AIRS LWV retrievals within 80 km of J31 profiles yield lower bias and RMS differences compared to AATS or Vaisala retrievals than do AIRS retrievals within 150 km of the J31. In particular, for AIRS-minus-AATS LWV differences, the bias decreases from 8.8% to 5.8%, and the RMS difference decreases from 21.5% to 16.4%. Comparison of vertically resolved AIRS water vapor retrievals (LWV_A) to AATS values in fixed pressure layers yields biases of −2% to +6% and RMS differences of ∼20% below 700 hPa. Variability and magnitude of these differences increase significantly above 700 hPa. MODIS IR retrievals of CWV in 205 grid cells (5 × 5 km at nadir) are biased wet by 10.4% compared to AATS over-ocean near-surface retrievals. The MODIS-Aqua subset (79 grid cells) exhibits a wet bias of 5.1%, and the MODIS-Terra subset (126 grid cells) yields a wet bias of 13.2%. Received 3 July 2006; accepted 12 February 2007; published 6 June 2007. Keywords: airborne Sun photometer; columnar water vapor; satellite validation. Index Terms: 0360 Atmospheric Composition and Structure: Radiation: transmission and scattering; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques. Read Full Article (file size: 3306692 bytes) Cited by Citation: Livingston, J., et al. (2007), Comparison of water vapor measurements by airborne Sun photometer and near-coincident in situ and satellite sensors during INTEX/ITCT 2004, J. Geophys. Res., 112, D12S16, doi:10.1029/2006JD007733. Copyright 2007 by the American Geophysical Union.

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