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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

Abstract : We document, for the first time, how detailed ver-tical profiles of cloud fraction (CF) change diurnally be-tween 51◦S and 51◦N, by taking advantage of 15 monthsof measurements from the Cloud-Aerosol Transport Sys-tem (CATS) lidar on the non-sun-synchronous InternationalSpace Station (ISS).Over the tropical ocean in summer, we find few highclouds during daytime. At night they become frequent over alarge altitude range (11–16 km between 22:00 and 04:00 LT).Over the summer tropical continents, but not over ocean,CATS observations reveal mid-level clouds (4–8 km abovesea level or a.s.l.) persisting all day long, with a weak di-urnal 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 timeshifted, with high-altitude clouds following the changes inlow-altitude clouds by several hours. Over all continents atall latitudes during summer, the low-level clouds develop up-wards and reach a maximum occurrence at about 2.5 km a.s.l.in the early afternoon (around 14:00).Our work also shows that (1) the diurnal cycles of ver-tical profiles derived from CATS are consistent with thosefrom ground-based active sensors on a local scale, (2) thecloud profiles derived from CATS measurements at localtimes of 01:30 and 13:30 are consistent with those observedfrom CALIPSO at similar times, and (3) the diurnal cyclesof low and high cloud amounts (CAs) derived from CATS are in general in phase with those derived from geostationaryimagery but less pronounced. Finally, the diurnal variabilityof cloud profiles revealed by CATS strongly suggests thatCALIPSO measurements at 01:30 and 13:30 document thedaily extremes of the cloud fraction profiles over ocean andare more representative of daily averages over land, exceptat altitudes above 10 km where they capture part of the diur-nal variability. These findings are applicable to other instru-ments with local overpass times similar to CALIPSO’s, suchas all the other A-Train instruments and the future Earth-CARE mission.
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Vincent Noël, Hélène Chepfer, Marjolaine Chiriaco, John Yorks. 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. Atmospheric Chemistry and Physics, European Geosciences Union, 2018, 18, pp.9457-9473. ⟨10.5194/acp-18-9457-2018⟩. ⟨insu-01754601⟩

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