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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2019-125
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-125
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Apr 2019

Submitted as: research article | 26 Apr 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Measurement Techniques (AMT).

Above-Cloud Aerosol Radiative Effects based on ORACLES 2016 and ORACLES 2017 Aircraft Experiments

Sabrina P. Cochrane1,2, K. Sebastian Schmidt1,2, Hong Chen1,2, Peter Pilewskie1,2, Scott Kittelman1, Jens Redemann3, Samuel LeBlanc4, Kristina Pistone4, Meloë Kacenelenbogen4, Michal Segal Rozenhaimer4, Yohei Shinozuka5, Connor Flynn6, Steven Platnick7, Kerry Meyer7, Rich Ferrare8, Sharon Burton8, Chris Hostetler8, Steven Howell9, Amie Dobracki10, and Sarah Doherty11 Sabrina P. Cochrane et al.
  • 1Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, 80303, USA
  • 2Laboratory for Atmospheric and Space Physics, Boulder, 80303, USA
  • 3School of Meteorology, University of Oklahoma, Norman, Oklahoma, 73019, USA
  • 4Bay Area Environmental Research Institute/NASA Ames Research Center, Mountain View, 94035, USA
  • 5Universities Space Research Association/NASA Ames Research Center, Mountain View, 94035, USA
  • 6Pacific Northwest National Laboratory, Richland, Washington, 99354, USA
  • 7NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 8NASA Langley Research Center, Hampton, VA 23666, USA
  • 9Departmentof Oceanography, University of Hawaii, Honolulu, HI 96844, USA
  • 10Department of Atmospheric Science, Rosentiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33146, USA
  • 11Joint Institute for the Study of Atmosphere and Ocean, University of Washington, Seattle, WA 98195, USA

Abstract. Determining the direct aerosol radiative effect (DARE) of absorbing aerosols above clouds from satellite observations alone is a challenging task, in part because the radiative signal of the aerosol layer is not easily untangled from that of the clouds below. In this study, we use aircraft measurements from the NASA ObseRvations of CLouds above Aerosols and their intEractionS (ORACLES) project in the southeast Atlantic to derive it with as few assumptions as possible. This is accomplished by using spectral irradiance measurements (Solar Spectral Flux Radiometer, SSFR) and aerosol optical depth (AOD) retrievals (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research, 4STAR) during vertical profiles (spirals) that minimize the albedo variability of the underlying cloud field – thus isolating aerosol radiative effects from those of the cloud field below. For two representative cases, we retrieve spectral aerosol single scattering albedo (SSA) and the asymmetry parameter (g) from these profile measurements, and calculate DARE given the albedo range measured by SSFR on horizontal legs above clouds. For mid-visible wavelengths, we find SSA values from 0.80–0.85, and a significant spectral dependence of g. As the cloud albedo increases, the aerosol increasingly warms the column. The transition from a cooling to a warming top-of-aerosol radiative effect (the critical albedo) occurs just above 0.2 in the mid-visible. In a companion paper, we use the techniques introduced here to generalize our findings to all 2016 and 2017 measurements, and parameterize aerosol radiative effects.

Sabrina P. Cochrane et al.
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Sabrina P. Cochrane et al.
Sabrina P. Cochrane et al.
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Short summary
For two cases from the NASA ORACLES experiments, we retrieve aerosol and cloud properties and calculate direct aerosol radiative effects (DARE). We investigate the relationship between DARE and the cloud albedo by specifying the albedo for which DARE transitions from a cooling to warming radiative effect. Our new aerosol retrieval algorithm is successful despite complexities associated with scenes that contain aerosols above clouds and decreases the uncertainty on retrieved aerosol parameters.
For two cases from the NASA ORACLES experiments, we retrieve aerosol and cloud properties and...
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