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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/amt-2020-140
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-140
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 May 2020

Submitted as: research article | 18 May 2020

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This preprint is currently under review for the journal AMT.

A new OCO-2 cloud flagging and rapid retrieval of marine boundary layer cloud properties

Mark Richardson1,2, Matthew D. Lebsock1, James McDuffie1, and Graeme L. Stephens1,2,3 Mark Richardson et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
  • 2Colorado State University, Fort Collins, CO 90095, USA
  • 3Department of Meteorology, University of Reading, RG6 7BE, UK

Abstract. The Orbiting Carbon Observatory-2 (OCO-2) carries a hyperspectral A-band sensor that can obtain information about cloud geometric thickness (H). The OCO2CLD-LIDAR-AUX product retrieved H with the aid of collocated CALIPSO lidar data to identify suitable clouds and provide a priori cloud-top pressure (Ptop). This collocation is no longer possible since CALIPSO's coordination flying with OCO-2 has ended, so here we introduce a new cloud flagging and a priori assignment using only OCO-2 data, restricted to ocean footprints where solar zenith angle < 45°. Firstly, a multi-layer perceptron network was trained to identify liquid clouds over ocean with sufficient optical depth (τ > 1) for a valid retrieval, and agreement with MODIS-CALIPSO is 90.0 %. Secondly, we developed a lookup table to simultaneously retrieve cloud τ, effective radius (re) and Ptop from A-band and CO2 band radiances. Median Ptop difference versus CALIPSO is 12 hPa with interdecile range [−11,87] hPa, substantially better than the MODIS-CALIPSO [−83,81] hPa. The MODIS-OCO-2 τ difference is 0.8 (−3.8,6.9) and re is −0.3 [−2.8,2.1] μm. The tau difference is due to optically thick and horizontally heterogeneous cloud scenes. As well as an improved passive Ptop retrieval, this a priori information will allow a purely OCO-2 based Bayesian retrieval of cloud droplet number concentration (Nd). Finally, our cloud flagging procedure may also be useful for future partial column above-cloud CO2 abundance retrievals.

Mark Richardson et al.

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Mark Richardson et al.

Mark Richardson et al.

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Short summary
We previously combined data from a lidar on the CALIPSO satellite and measurements of reflected sunlight from the OCO-2 satellite to get new information about low clouds over oceans. The satellites are no longer formation flying, so this work is a step towards getting unique new information about these clouds using OCO-2 data only. We show we can rapidly and accurately identify liquid oceanic clouds and obtain their height better than a widely-used passive sensor.
We previously combined data from a lidar on the CALIPSO satellite and measurements of reflected...
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