A42A-08
Implications of using transmitted vs. reflected light for determining cloud properties, cloud radiative effects and aerosol-cloud-interactions

Thursday, 17 December 2015: 12:05
3002 (Moscone West)
Samuel E LeBlanc1,2, Jens Redemann1, Michal Segal-Rosenhaimer1,3, Meloe S Kacenelenbogen1,3, Yohei Shinozuka1,3, Connor Joseph Flynn4, Sebastian Schmidt5, Peter Pilewskie5, Shi Song5, Sarah Woods6, Paul Lawson6, Athanasios Nenes7, Jack J Lin8 and Luke D Ziemba9, (1)NASA Ames Research Center, Moffett Field, CA, United States, (2)Oak Ridge Associated Universities Inc., Oak Ridge, TN, United States, (3)Bay Area Environmental Research Institute Sonoma, Sonoma, CA, United States, (4)Pacific Northwest National Laboratory, Richland, WA, United States, (5)University of Colorado, Boulder, CO, United States, (6)SPEC Inc, Boulder, CO, United States, (7)Georgia Institute of Technology, Atlanta, GA, United States, (8)Georgia Institute of Technology Main Campus, Atlanta, GA, United States, (9)NASA Langley Research Center, Hampton, VA, United States
Abstract:
Light transmitted through clouds is sensitive to a different cloud volume than reflected light at cloud top. This difference in sampling volumes has implications when calculating the radiative effects of clouds (CRE) and aerosol-cloud-interactions (ACI). We present a comparison of retrieved cloud properties and the corresponding CRE and ACI based on transmitted and reflected light for a cloud sampled during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS, 2013) field campaign. Measurements of zenith radiances were obtained from the NASA DC-8 aircraft using the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) instrument. 4STAR was deployed on an airborne platform during SEAC4RS alongside the Solar Spectral Flux Radiometer (SSFR).

To retrieve cloud properties from transmitted shortwave radiation, we use a retrieval utilizing spectrally resolved measurements. Spectral features in shortwave radiation transmitted through clouds are sensitive to changes in cloud optical thickness, effective radius, and thermodynamic phase. The spectral features due to absorption and scattering processes by liquid water and ice cloud particles include shifts in spectral slopes, curvatures, maxima, and minima of cloud-transmitted radiance. These spectral features have been quantified by 15 parameters used to retrieve cloud properties from the 4STAR zenith radiances. Retrieved cloud optical thicknesses and effective radii based on transmitted shortwave radiation are compared to their counterparts obtained from reflected shortwave radiation measured above cloud with MODIS and with the enhanced MODIS Airborne Simulator (eMAS), the Research Scanning Polarimeter (RSP), and SSFR operating aboard the NASA ER-2 aircraft. Remotely sensed cloud particle effective radius are combined with in situ measurements of cloud and aerosol particles from the NASA Langley Aerosol Research Group Experiment (LARGE) CCN Counter and the cloud probes from SPEC Inc. By using the combination of in situ and remote sensors, we present an estimate of ACI at cloud base.

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