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Volume 18, issue 13 | Copyright
Atmos. Chem. Phys., 18, 9457-9473, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Jul 2018

Research article | 06 Jul 2018

The diurnal cycle of cloud profiles over land and ocean between 51° S and 51° N, seen by the CATS spaceborne lidar from the International Space Station

Vincent Noel1, Hélène Chepfer2, Marjolaine Chiriaco3, and John Yorks4 Vincent Noel et al.
  • 1Laboratoire d'Aérologie, CNRS/UPS, Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, Toulouse, France
  • 2LMD/IPSL, Sorbonne Université, École polytechnique, École Normale Supérieure, PSL Research University, CNRS, 91120 Palaiseau, France
  • 3LATMOS/IPSL, Univ. Versailles Saint-Quentin en Yvelines, Guyancourt, France
  • 4NASA GSFC, Greenbelt, Maryland, USA

Abstract. We document, for the first time, how detailed vertical profiles of cloud fraction (CF) 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).

Over the tropical ocean in summer, we find few high clouds during daytime. At night they become frequent over a large altitude range (11–16km between 22:00 and 04:00LT). Over the summer tropical continents, but not over ocean, CATS observations reveal mid-level clouds (4–8km above sea level or a.s.l.) persisting all day long, with a weak diurnal cycle (minimum at noon). Over the Southern Ocean, diurnal cycles appear for the omnipresent low-level clouds (minimum between noon and 15:00) and high-altitude clouds (minimum between 08:00 and 14:00). Both cycles are time shifted, with high-altitude clouds following the changes in low-altitude clouds by several hours. Over all continents at all latitudes during summer, the low-level clouds develop upwards and reach a maximum occurrence at about 2.5kma.s.l. in the early afternoon (around 14:00).

Our work also shows that (1) the diurnal cycles of vertical profiles derived from CATS are consistent with those from ground-based active sensors on a local scale, (2) 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, and (3) the diurnal cycles of low and high cloud amounts (CAs) derived from CATS are in general in phase with those derived from geostationary imagery but less pronounced. Finally, the diurnal variability of cloud profiles revealed by CATS strongly suggests that CALIPSO measurements at 01:30 and 13:30 document the daily extremes of the cloud fraction profiles over ocean and are more representative of daily averages over land, except at altitudes above 10km where they capture part of the diurnal variability. These findings are applicable to other instruments with local overpass times similar to CALIPSO's, such as all the other A-Train instruments and the future EarthCARE mission.

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Short summary
From 3 years of observations from the CATS lidar on the International Space Station we document the daily cycle of the vertical distribution of clouds. This is the first time this is documented over several continents and oceans using finely resolved measurements on a near-global scale from a single instrument. We show that other instruments observing clouds from space, like CALIPSO, document extremes of the daily cycle over ocean and closer to the average over land.
From 3 years of observations from the CATS lidar on the International Space Station we document...