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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 21 Nov 2018

Research article | 21 Nov 2018

Review status
This discussion paper is a preprint. A revision of the manuscript was accepted for the journal Atmospheric Measurement Techniques (AMT).

Liquid marine cloud geometric thickness retrieved from OCO-2's oxygen A-band spectrometer

Mark Richardson1,2, Jussi Leinonen1, Heather Q. Cronk3, James McDuffie1, Matthew D. Lebsock1, and Graeme L. Stephens1,4 Mark Richardson et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91125, USA
  • 2Joint Institute for Regional Earth System Science and Engineering, University of California Los Angeles, Los Angeles, CA 90095, USA
  • 3Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, CO 80521, USA
  • 4Department of Meteorology, University of Reading, Reading, RG6 6BB, UK

Abstract. This paper introduces the OCO2CLD-LIDAR-AUX product, which uses the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar and the Orbiting Carbon Observatory-2 (OCO-2) hyperspectral A-band spectrometer. CALIPSO provides a prior cloud top pressure (Ptop) for an OCO-2 based retrieval of cloud optical depth, Ptop and cloud geometric thickness expressed in hPa. Measurements are of single-layer liquid clouds over oceans from September 2014 to December 2016 when collocated data are available. Retrieval performance is best for solar zenith angle < 45° and when the cloud phase classification, which also uses OCO-2's weak CO2 band, is more confident. The highest quality optical depth retrievals agree with those from the Moderate Resolution Imaging Spectroradiometer (MODIS) with discrepancies smaller than the MODIS-reported uncertainty. Retrieved thicknesses are consistent with a substantially subadiabatic structure over marine stratocumulus regions, in which extinction is weighted towards the cloud top. Cloud top pressure in these clouds shows a 4 hPa bias compared with CALIPSO which we attribute mainly to the assumed vertical structure of cloud extinction after showing little sensitivity to the presence of CALIPSO-identified aerosol layers or assumed cloud droplet effective radius. This is the first case of success in obtaining internal cloud structure from hyperspectral A-band measurements and exploits otherwise unused OCO-2 data. The data provided by these retrievals provide additional constraints on satellite-based estimates of cloud droplet number concentration from visible imagery, which rely on parameterization of the cloud thickness.

Mark Richardson et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Mark Richardson et al.
Mark Richardson et al.
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Publications Copernicus
Short summary
We retrieve cloud properties, including geometric thickness, by combining hyperspectral Orbiting Carbon Observatory-2 (OCO-2) A-band measurements with CALIPSO lidar. This uses cloudy scene data that are not used in OCO-2's main mission, which is target at clear-sky atmospheric CO2 abundance. This is the first retrieval using such hyperspectral information and promises to provide a unique constraint on the properties of low, liquid clouds over the ocean.
We retrieve cloud properties, including geometric thickness, by combining hyperspectral Orbiting...