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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/acp-2018-1008
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1008
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Nov 2018

Research article | 15 Nov 2018

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

Evaluating Models' Response Of Tropical Low Clouds to SST Forcings Using CALIPSO Observations

Gregory Cesana1,2,4, Anthony D. Del Genio2, Andrew S. Ackerman2, Maxwell Kelley3,2, Gregory Elsaesser4,2, Ann M. Fridlind2, Ye Cheng1,2, and Mao-Sung Yao3,2 Gregory Cesana et al.
  • 1Columbia University, Center for Climate Systems Research, Earth Institute, New York, NY
  • 2NASA Goddard Institute for Space Studies, New York, NY
  • 3SciSpace LLC, Institute for Space Studies, New York, NY
  • 4Columbia University, Department of Applied Physics and Applied Mathematics, New York, NY

Abstract. Recent studies have shown that in response to a surface warming, the marine tropical low-cloud cover (LCC) as observed by passive sensor satellites substantially decreases, therefore generating a smaller negative value of the top-of-the-atmosphere cloud radiative effect (CRE). Here we study the LCC and CRE interannual changes in response to sea surface temperature (SST) forcings in the GISS Model E2 climate model, a developmental version of the GISS Model E3 climate model, and in 12 other climate models, as a function of their ability to represent the vertical structure of the cloud response to SST change against 10 years of CALIPSO observations. The more realistic models (those that satisfy the observational constraint) capture the observed interannual LCC change quite well (ΔLCC/ΔSST=−3.49±1.01%K−1 vs. ΔLCC/ΔSSTobs=−3.59±0.28%K−1) while the others largely underestimate it (ΔLCC/ΔSST=−1.32±1.28%K−1). Consequently, the more realistic models simulate more positive shortwave feedback (ΔCRE/ΔSST=2.60±1.13Wm−2K−1) than the less realistic models (ΔCRE/ΔSST=0.87±2.63Wm−2K−1), in better agreement with the observations (ΔCRE/ΔSSTobs=3.05±0.28Wm−2K−1), although slightly underestimated. The ability of the models to represent moist processes within the planetary boundary layer and produce persistent stratocumulus decks appears crucial to replicating the observed relationship between clouds, radiation and surface temperature. This relationship is different depending on the type of low cloud in the observations. Over stratocumulus regions, cloud top height increases slightly with SST, accompanied by a large decrease of cloud fraction, whereas over trade cumulus regions, cloud fraction decreases everywhere, to a smaller extent.

Gregory Cesana et al.
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Interactive discussion
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Gregory Cesana et al.
Gregory Cesana et al.
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Short summary
The response of low-clouds to climate change (i.e., cloud feedbacks) is still pointed out as being the largest source of uncertainty in climate models. Here we use CALIPSO observations to discriminate climate models that reproduce observed interannual change of cloud fraction with SST forcings, referred to as a present-day cloud feedback. Modeling moist processes in the planetary boundary layer is crucial to produce large stratocumulus decks and realistic present-day cloud feedbacks.
The response of low-clouds to climate change (i.e., cloud feedbacks) is still pointed out as...
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