Satellite retrieval of cloud condensation nuclei concentrations by using clouds as CCN chambers
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Rosenfeld, Daniel, Youtong Zheng, Eyal Hashimshoni, Mira L. Pöhlker, Anne Jefferson, Christopher Pöhlker, Xing Yu, et al. “Satellite Retrieval of Cloud Condensation Nuclei Concentrations by Using Clouds as CCN Chambers.” Proceedings of the National Academy of Sciences 113, no. 21 (March 4, 2016): 5828–34. https://doi.org/10.1073/pnas.1514044113.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
Quantifying the aerosol/cloud-mediated radiative effect at a global scale requires simultaneous satellite retrievals of cloud condensation nuclei (CCN) concentrations and cloud base updraft velocities (Wb). Hitherto, the inability to do so has been a major cause of high uncertainty regarding anthropogenic aerosol/cloud-mediated radiative forcing. This can be addressed by the emerging capability of estimating CCN and Wb of boundary layer convective clouds from an operational polar orbiting weather satellite. Our methodology uses such clouds as an effective analog for CCN chambers. The cloud base supersaturation (S) is determined by Wb and the satellite-retrieved cloud base drop concentrations (Ndb), which is the same as CCN(S). Validation against ground-based CCN instruments at Oklahoma, at Manaus, and onboard a ship in the northeast Pacific showed a retrieval accuracy of ±25% to ±30% for individual satellite overpasses. The methodology is presently limited to boundary layer not raining convective clouds of at least 1 km depth that are not obscured by upper layer clouds, including semitransparent cirrus. The limitation for small solar backscattering angles of <25° restricts the satellite coverage to ~25% of the world area in a single day.