Dataset Information

Frequency and causes of failed MODIS cloud property retrievals for liquid phase clouds over global oceans.

ABSTRACT: Moderate Resolution Imaging Spectroradiometer (MODIS) retrieves cloud droplet effective radius (re ) and optical thickness (?) by projecting observed cloud reflectances onto a precomputed look-up table (LUT). When observations fall outside of the LUT, the retrieval is considered "failed" because no combination of ? and re within the LUT can explain the observed cloud reflectances. In this study, the frequency and potential causes of failed MODIS retrievals for marine liquid phase (MLP) clouds are analyzed based on 1?year of Aqua MODIS Collection 6 products and collocated CALIOP and CloudSat observations. The retrieval based on the 0.86?µm and 2.1?µm MODIS channel combination has an overall failure rate of about 16% (10% for the 0.86?µm and 3.7?µm combination). The failure rates are lower over stratocumulus regimes and higher over the broken trade wind cumulus regimes. The leading type of failure is the "re too large" failure accounting for 60%-85% of all failed retrievals. The rest is mostly due to the "re too small" or ? retrieval failures. Enhanced retrieval failure rates are found when MLP cloud pixels are partially cloudy or have high subpixel inhomogeneity, are located at special Sun-satellite viewing geometries such as sunglint, large viewing or solar zenith angles, or cloudbow and glory angles, or are subject to cloud masking, cloud overlapping, and/or cloud phase retrieval issues. The majority (more than 84%) of failed retrievals along the CALIPSO track can be attributed to at least one or more of these potential reasons. The collocated CloudSat radar reflectivity observations reveal that the remaining failed retrievals are often precipitating. It remains an open question whether the extremely large re values observed in these clouds are the consequence of true cloud microphysics or still due to artifacts not included in this study.

SUBMITTER: Cho HM

PROVIDER: S-EPMC5012132 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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Frequency and causes of failed MODIS cloud property retrievals for liquid phase clouds over global oceans.

Cho Hyoun-Myoung HM Zhang Zhibo Z Meyer Kerry K Lebsock Matthew M Platnick Steven S Ackerman Andrew S AS Di Girolamo Larry L C-Labonnote Laurent L Cornet Céline C Riedi Jerome J Holz Robert E RE

Journal of geophysical research. Atmospheres : JGR 20150509 9

Moderate Resolution Imaging Spectroradiometer (MODIS) retrieves cloud droplet effective radius (re ) and optical thickness (τ) by projecting observed cloud reflectances onto a precomputed look-up table (LUT). When observations fall outside of the LUT, the retrieval is considered "failed" because no combination of τ and re within the LUT can explain the observed cloud reflectances. In this study, the frequency and potential causes of ...[more]

PMID: 27656330

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Project description:We investigated the view angle dependence of domain mean Moderate Resolution Imaging Spectroradiometer (MODIS) liquid water path (LWP) and that of corresponding cloud optical thickness, effective radius, and liquid cloud fraction as proxy for plane-parallel retrieval biases. Independent Advanced Microwave Scanning Radiometer-EOS LWP was used to corroborate that the observed variations with sun-view geometry were not severely affected by seasonal/latitudinal changes in cloud properties. Microwave retrievals showed generally small (<10%) cross-swath variations. The view angle (cross-swath) dependence of MODIS optical thickness was weaker in backscatter than forward scatter directions and transitioned from mild ? shape to stronger ? shape as heterogeneity, sun angle, or latitude increased. The 2.2 µm effective radius variations always had a ? shape, which became pronounced and asymmetric toward forward scatter in the most heterogeneous clouds and/or at the lowest sun. Cloud fraction had the strongest and always ?-shaped view angle dependence. As a result, in-cloud MODIS cloud liquid water path (CLWP) showed surprisingly good view angle (cross-swath) consistency, usually comparable to that of microwave retrievals, due to cancelation between optical thickness and effective radius biases. Larger (20-40%) nadir-relative increases were observed in the most extreme heterogeneity and sun angle bins, that is, typically in the polar regions, which, however, constituted only 3-8% of retrievals. The good consistency of MODIS in-cloud CLWP was lost for gridbox mean LWP, which was dominated by the strong cloud fraction increase with view angle. More worryingly, MODIS LWP exhibited significant and systematic absolute increases with heterogeneity and sun angle that is not present in microwave LWP.Key pointsMicrowave LWP shows small overall and cross-swath variationsMODIS in-cloud LWP also shows good view angle consistency in most casesMODIS retrievals show strong overall increase with heterogeneity and sun angle.

Dataset Information

Frequency and causes of failed MODIS cloud property retrievals for liquid phase clouds over global oceans.

Publications

Frequency and causes of failed MODIS cloud property retrievals for liquid phase clouds over global oceans.

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