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Polarized View of Supercooled Liquid Water CloudsSupercooled liquid water (SLW) clouds, where liquid droplets exist at temperatures below 0 C present a well known aviation hazard through aircraft icing, in which SLW accretes on the airframe. SLW clouds are common over the Southern Ocean, and climate-induced changes in their occurrence is thought to constitute a strong cloud feedback on global climate. The two recent NASA field campaigns POlarimeter Definition EXperiment (PODEX, based in Palmdale, California, January-February 2013) and Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS, based in Houston, Texas in August- September 2013) provided a unique opportunity to observe SLW clouds from the high-altitude airborne platform of NASA's ER-2 aircraft. We present an analysis of measurements made by the Research Scanning Polarimeter (RSP) during these experiments accompanied by correlative retrievals from other sensors. The RSP measures both polarized and total reflectance in 9 spectral channels with wavelengths ranging from 410 to 2250 nm. It is a scanning sensor taking samples at 0.8deg intervals within 60deg from nadir in both forward and backward directions. This unique angular resolution allows for characterization of liquid water droplet size using the rainbow structure observed in the polarized reflectances in the scattering angle range between 135deg and 165deg. Simple parametric fitting algorithms applied to the polarized reflectance provide retrievals of the droplet effective radius and variance assuming a prescribed size distribution shape (gamma distribution). In addition to this, we use a non-parametric method, Rainbow Fourier Transform (RFT),which allows retrieval of the droplet size distribution without assuming a size distribution shape. We present an overview of the RSP campaign datasets available from the NASA GISS website, as well as two detailed examples of the retrievals. In these case studies we focus on cloud fields with spatial features varying between glaciated and liquid phases at altitudes as high as 10 km, which correspond to temperatures close to the homogeneous freezing temperature of pure water drops (about -35 C or colder). The multimodal droplet size distributions retrieved from RSP data in these cases are consistent with the multi-layer cloud structure observed by correlative Cloud Physics Lidar (CPL) measurements.
Document ID
20160007567
Document Type
Reprint (Version printed in journal)
Authors
Alexandrov, Mikhail D. (Columbia Univ. New York, NY, United States)
Cairns, Brian (NASA Goddard Inst. for Space Studies New York, NY United States)
Van Diedenhoven, Bastiaan (Columbia Univ. New York, NY, United States)
Ackerman, Andrew S. (NASA Goddard Inst. for Space Studies New York, NY United States)
Wasilewski, Andrzej P. (TRINNOVIM, LLC New York, NY, United States)
McGill, Matthew J. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Yorks, John E. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Hlavka, Dennis L. (Science Systems and Applications, Inc. Lanham, MD, United States)
Platnick, Steven E. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Arnold, G. Thomas (Science Systems and Applications, Inc. Lanham, MD, United States)
Date Acquired
June 15, 2016
Publication Date
April 22, 2016
Publication Information
Publication: Remote Sensing of Environment
Volume: 181
Subject Category
Meteorology and Climatology
Report/Patent Number
GSFC-E-DAA-TN31822
Funding Number(s)
CONTRACT_GRANT: NNG12HP08C
CONTRACT_GRANT: NNG12HP07C
CONTRACT_GRANT: NNX14AB99A
Distribution Limits
Public
Copyright
Other
Keywords
Clouds
Supercooled water
Remote sensing
Electromagneteic scattering
Mie theory
Rainbow
Polarization