Constraining the models' response of tropical clouds to SST forcings using CALIPSO observations

Gregory Cesana; Anthony D. Del Genio; Andrew Ackerman

doi:10.1117/12.2324800

23 October 2018 Constraining the models' response of tropical clouds to SST forcings using CALIPSO observations

Gregory Cesana, Anthony D. Del Genio, Andrew Ackerman

Proceedings Volume 10782, Remote Sensing and Modeling of the Atmosphere, Oceans, and Interactions VII; 107820A (2018) https://doi.org/10.1117/12.2324800
Event: SPIE Asia-Pacific Remote Sensing, 2018, Honolulu, Hawaii, United States

Abstract

Here we present preliminary results from the analysis of the low cloud cover (LCC) and cloud radiative effect (CRE) interannual changes in response to sea surface temperature (SST) forcings in two GISS climate models, and 12 other climate models. We further classify them as a function of their ability to reproduce the vertical structure of the cloud response to SST change against 10 years of CALIPSO observations: “the constrained models, which match the observation constraint, and the unconstrained models”. The constrained models replicate the observed interannual LCC change particularly well (ΔLCC_con=-3.49 ±1.01 %/K vs. ΔLCC_obs=-3.59 ±0.28 %/K) as opposed to the unconstrained models, which largely underestimate it (ΔLCC_unc = -1.32 ± 1.28 %/K). As a result, the amount of short-wave warming simulated by the constrained models (ΔCRE_con=2.60 ±1.13 W/m² /K) is in better agreement with the observations (ΔCRE_obs=3.05 ± 0.28 W/m² /K) than the unconstrained models (ΔCRE_con=0.87 ±2.63 W/m² /K). Depending on the type of low cloud, the observed relationship between cloud/radiation and surface temperature varies. Over the stratocumulus regions, increasing SSTs generate higher cloud top height along with a large decrease of the cloud fraction below as opposed to a slight decrease of the cloud fraction at each level over the trade cumulus regions. Our results suggest that the models must generate sustainable stratocumulus decks and moist processes in the planetary boundary layer to reproduce these observed features. Future work will focus on defining a method to objectively discriminate these cloud types that can be applied consistently in both the observations and the models.

Citation Download Citation

Gregory Cesana, Anthony D. Del Genio, and Andrew Ackerman "Constraining the models' response of tropical clouds to SST forcings using CALIPSO observations", Proc. SPIE 10782, Remote Sensing and Modeling of the Atmosphere, Oceans, and Interactions VII, 107820A (23 October 2018); https://doi.org/10.1117/12.2324800

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