A054-06
Evaluation of MODIS and Himawari-8 Low Clouds Retrievals over the Southern Ocean with In Situ Measurements from the SOCRATES Campaign

Tuesday, 8 December 2020: 19:20
Virtual
Litai Kang1, Roger Marchand1, William L Smith Jr2 and SOCRATES Science Team, (1)University of Washington, Department of Atmospheric Sciences, Seattle, WA, United States, (2)NASA Langley Research Ctr, Hampton, VA, United States
Recorded Presentation
Abstract:
Satellite retrievals of cloud properties have been widely used to study clouds over the Southern Ocean, but our confidence in these retrievals has been limited by a lack of verification studies and in situ observations. In this study, in-situ aircraft measurements from the Southern Ocean Cloud Radiation Aerosol Transport Experimental Study (SOCRATES) are used to evaluate cloud properties of low clouds from three satellite-imager retrievals that are based on the bi-spectral technique: (i) The operational Moderate Resolution Imaging Spectroradiometer (MODIS) level 2 (collection 6.1) cloud product, (ii) The CERES-MODIS Edition 4 cloud product, and (iii) the NASA SatCORPS Himawari-8 cloud product. We evaluate the retrieved cloud optical depth, effective radius, liquid water path, and cloud droplet number concentration.

Overall the satellite retrievals compare well with the in situ data with little bias (no statistically significant bias at the 95% level of confidence) and modest to good correlation coefficients, when considering all aircraft profiles for which there are coincident MODIS observations. The SatCORPS Himawari-8 product does, however, show a statistically significant mean bias of about 1.2 μm for effective radius and 2.6 for optical depth when applied to a larger set of profiles with coincident Himawari-8 observations.

A close examination of the data shows that the low overall mean-bias in the retrievals is due in part to compensating errors between cases (profiles) that are non- or lightly-precipitating, with cases that have heavier precipitation (precipitation water path> 10 gm-2). The effective radius is slightly biased high (by about 0.5 to 1.0 μm) for non- and lightly-precipitating cases and biased low by a large amount (about 3 to 4 μm) for more heavily-precipitating cases. The bias in non- and lightly-precipitating conditions is due (at least in part) to having an assumed drop size distribution (DSD) in the retrieval that is too broad. For heavily-precipitating cases, large biases occurred when significant precipitation was found near cloud top. These biases in the effective radius ultimately propagate into the retrieved liquid water path and number concentration.

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