Variability of low-level clouds over the southern oceans

• Main Authors: Bazantay, Clément, Jourdan, Olivier, Mioche, Guillaume, Delanoë, Julien, Cazenave, Quitterie, Uitz, Julia, Sellegri, Karine
• Other Authors: Laboratoire de Météorologie Physique (LaMP), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA), SPACE - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'océanographie de Villefranche (LOV), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de la Mer de Villefranche (IMEV), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2022
• Subjects: [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; Sea ice; Southern Ocean; Weddell Sea
• Online Access: https://insu.hal.science/insu-03680894; https://doi.org/10.5194/egusphere-egu22-9550

International audience Climate model simulations of cloud radiative properties over the Southern Ocean (SO) show thatclouds reflect too little solar radiation compared with observations. This results in large errors inthe modelled sea surface temperature, atmospheric circulation and climate sensitivity. Low-level(LL) mixed-phase clouds (MPCs) in the cold sectors of extratropical cyclones are identified as themain contributor to the SO radiation bias.In this study, LL clouds are investigated between 40°S and 82° S to provide a new insight into theirgeographical distribution, as well as their spatial and temporal variabilities. The methodologyrelies on DARDAR products which exploits the synergy of CALIPSO's lidar and CloudSat's radarspace-borne remote sensing observations. Based on DARDAR cloud-type products, a cloudclassification program was developed to establish cloud spatial and temporal distributions. Thisstudy concerns all types of cloud, including MPCs and supercooled-water containing clouds. Themean seasonal LL cloud cover for 2007-2010 over oceans (including sea-ice) varies from 64.4% inwinter to 68.4% in fall. Larger cloud covers are observed between 50°S and 65°S where clouds arepresent more than 80% of the time. Dividing the studied area into smaller regions allowed toextract homogeneous sectors in term of cloud coverage. This analysis draw attention on someregions, such as the Tasman Sea sector that undergoes the highest seasonal variations for MPCand USLC occurrence, and the Argentinian coasts that presents important differences with otherregions at the same latitudes. Over the Southern Ocean, the Weddell Sea sector stands out with arelatively low LL cloud occurrence.Statistical analyses were carried out to determine the influence of the meteorological andbiological conditions on cloud occurrence. Even though air temperature drives all cloud-typeoccurrences, it was found that the lower-tropospheric stability (LTS) is a good predictor of ice-cloud occurrence between 40°S and 50°S, particularly. With ...