The Diurnal Cycles of Cloud Profiles and Water Vapor over Land and Ocean seen by the CATS Spaceborne Lidar and Megha-Tropiques Sensors

Abstract : We document, for the first time, how detailed vertical profiles of cloud fraction change diurnally between 51°S and 51°N, by taking advantage of 15 months of measurements from the Cloud-Aerosol Transport System (CATS) lidar on the non-sun-synchronous International Space Station (ISS). In the Tropics, we compare CATS observations to the diurnal cycles of water vapor profiles and top-of-the-atmosphere radiation revealed by the several sensors onboard the Megha-Tropiques low-orbiting platform. We explore the diurnal cycles of low-level and high-level clouds over the course of the day globally and in several large regions during the boreal summer. We find distinct behaviours for high clouds over the tropical ocean, for mid-level clouds over tropical land, and for the omnipresent low and high level clouds over the Southern Ocean. Over all continental areas, we see boundary layer clouds develop upwards following sunlight activation and reach maximum occurrence at about 2.5km a.s.l. early in the afternoon. We find that the cloud profiles derived from CATS measurements at local times of 01:30 and 13:30 are consistent with those observed from CALIPSO at similar times. Our results suggest that CALIPSO measurements, always sampled at local times of 01:30 and 13:30, document the daily extremes of the cloud fraction profiles, most accurately over ocean. These findings are applicable to other instruments with similar local overpass times, including all the other A-Train instruments and the upcoming EarthCARE mission. Finally, two robust behaviours in tropical regions dominated by subsidence are explained by comparison with Megha-Tropiques measurements: 1) over ocean, a positive anomaly of opaque clouds in the lower atmosphere grows from sunset to sunrise, dampening the diurnal variation of oceanic surface temperature. 2) over land, a positive relative moisture anomaly near the surface at sunrise turns into a positive anomaly of opaque clouds in the free troposphere in the early afternoon, and into a near-tropopause thin clouds positive anomaly early at night, before vanishing with sunrise. This results in a strong surface temperature diurnal variation (17K).
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https://hal-insu.archives-ouvertes.fr/insu-01979657
Contributor : Catherine Cardon <>
Submitted on : Sunday, January 13, 2019 - 5:25:35 PM
Last modification on : Monday, October 28, 2019 - 4:59:25 PM

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  • HAL Id : insu-01979657, version 1

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Vincent Noël, Hélène Chepfer, Marjolaine Chiriaco, Hélène Brogniez, John Yorks, et al.. The Diurnal Cycles of Cloud Profiles and Water Vapor over Land and Ocean seen by the CATS Spaceborne Lidar and Megha-Tropiques Sensors. ATMOS 2018, Nov 2018, Salzburg, Austria. ⟨insu-01979657⟩

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