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Satellite Observed Sensitivity of Tropical Clouds and Moisture to Sea Surface Temperature on Various Time and Space Scales: Part 2. Focus on Marine Low Level Clouds

Erik Höjgård‐olsen 1, 2, * Hélène Chepfer 1 Hélène Brogniez 2 
* Corresponding author
2 SPACE - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : This study examines how satellite observed relative humidity (RH) profiles, cloud covers and cloud altitudes vary with sea surface temperature (SST) in low cloud regions on different temporal and spatial scales over the tropical oceans (30°N-30°S). We split low clouds into optically opaque and optically thin clouds and characterize for the first time their altitude variations with SST using space lidar observations. On the process scale, the median instantaneous observations at high spatial resolution show simultaneously decreasing low opaque cloud top altitude, decreasing low opaque cloud cover, increasing middle-tropospheric RH and decreasing lower-tropospheric RH with SST. Collectively, these observational results suggest decreasing opaque marine boundary layer cloud cover and enhanced mixing between the middle and lower troposphere with SST on the process scale, consistent with previous Large-Eddy Simulation studies. The co-variations between opaque cloud cover and RH with SST are quantified on all time and space scales (from the process scale to the annual tropical mean scale). Meanwhile, on the process scale, low optically thin clouds, co-existing with opaque clouds, rise with SST (consistent with the literature mechanism), whilst the low optically thin cloud cover is insensitive to SST (not consistent with the literature mechanism). These results are then compared to a general circulation model, which captures the observed sign of change of opaque cloud cover and middle-tropospheric RH with SST but fails to reproduce the observed vertical shrinkage of low opaque clouds with SST and the variations of low thin clouds with SST.
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Submitted on : Thursday, August 18, 2022 - 8:06:56 AM
Last modification on : Friday, August 19, 2022 - 3:45:16 AM

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Erik Höjgård‐olsen, Hélène Chepfer, Hélène Brogniez. Satellite Observed Sensitivity of Tropical Clouds and Moisture to Sea Surface Temperature on Various Time and Space Scales: Part 2. Focus on Marine Low Level Clouds. Journal of Geophysical Research: Atmospheres, American Geophysical Union, 2022, 127 (6), pp.e2021JD035402. ⟨10.1029/2021JD035402⟩. ⟨insu-03586903⟩

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