title: 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 (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 ofτandrewithin 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 "retoo large" failure accounting for 60%-85% of all failed retrievals. The rest is mostly due to the "retoo small" orτretrieval 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 theremainingfailed retrievals are often precipitating. It remains an open question whether the extremely largerevalues observed in these clouds are the consequence of true cloud microphysics or still due to artifacts not included in this study.
authors.affiliation: Joint Center of Earth Systems Technology Baltimore Maryland USA.
authors.forename: Hyoun-Myoung
authors.initials: HM
authors.lastname: Cho
authors.affiliation: Joint Center of Earth Systems Technology Baltimore Maryland USA; Physics Department University of Maryland, Baltimore County Baltimore Maryland USA.
authors.forename: Zhibo
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: NASA Goddard Space Flight Center Greenbelt Maryland USA; Goddard Earth Science Technology and Research Universities Space Research Association Columbia Maryland USA.
authors.forename: Kerry
authors.initials: K
authors.lastname: Meyer
authors.affiliation: Jet Propulsion Laboratory Pasadena California USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Lebsock
authors.affiliation: NASA Goddard Space Flight Center Greenbelt Maryland USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Platnick
authors.affiliation: NASA Goddard Institute for Space Studies New York New York USA.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Ackerman
authors.affiliation: Department of Atmospheric Sciences University of Illinois at Urbana-Champaign Urbana Illinois USA.
authors.forename: Larry
authors.initials: L
authors.lastname: Di Girolamo
authors.affiliation: Laboratoire d'Optique Atmosphérique-Université des Sciences et Technologies de Lille/CNRS Villeneuve d'A scq France.
authors.forename: Laurent
authors.initials: L
authors.lastname: C-Labonnote
authors.affiliation: Laboratoire d'Optique Atmosphérique-Université des Sciences et Technologies de Lille/CNRS Villeneuve d'A scq France.
authors.forename: Céline
authors.initials: C
authors.lastname: Cornet
authors.affiliation: Laboratoire d'Optique Atmosphérique-Université des Sciences et Technologies de Lille/CNRS Villeneuve d'A scq France.
authors.forename: Jerome
authors.initials: J
authors.lastname: Riedi
authors.affiliation: Cooperative Institute for Meteorological Satellite Studies University of Wisconsin-Madison Madison Wisconsin USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Holz
keywords: A‐Train; MODIS; cloud; drizzle; failure; inhomogeneity