Challenging and Improving the Simulation of Mid‐Level Mixed‐Phase Clouds Over the High‐Latitude Southern Ocean

• Published in: Journal of Geophysical Research: Atmospheres
• Main Authors: Vignon, É., Alexander, S., Demott, P., Sotiropoulou, G., Gerber, F., Hill, T., Marchand, R., Nenes, A., Berne, A.
• Other Authors: Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), University of Tasmania Hobart, Australia (UTAS), Colorado State University Fort Collins (CSU), Stockholm University, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, University of Washington Seattle
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Antarctica; ice nuclei particles; microphysics; mixed-phase clouds; Southern Ocean; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Austral; Antarc*
• Online Access: https://hal.sorbonne-universite.fr/hal-03280181; https://hal.sorbonne-universite.fr/hal-03280181/document; https://hal.sorbonne-universite.fr/hal-03280181/file/Vignon%20et%20al.%20-%202021%20-%20Challenging%20and%20Improving%20the%20Simulation%20of%20Mid-Le.pdf; https://doi.org/10.1029/2020JD033490

International audience Climate models exhibit major radiative biases over the Southern Ocean owing to a poor representation of mixed-phase clouds. This study uses the remote-sensing dataset from the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean (MARCUS) campaign to assess the ability of the Weather Research and Forecasting (WRF) model to reproduce frontal clouds off Antarctica. It focuses on the modeling of thin mid-level supercooled liquid water layers which precipitate ice. The standard version of WRF produces almost fully glaciated clouds and cannot reproduce cloud top turbulence. Our work demonstrates the importance of adapting the ice nucleation parameterization to the pristine austral atmosphere to reproduce the supercooled liquid layers. Once simulated, droplets significantly impact the cloud radiative effect by increasing downwelling longwave fluxes and decreasing downwelling shortwave fluxes at the surface. The net radiative effect is a warming of snow and ice covered surfaces and a cooling of the ocean. Despite improvements in our simulations, the local turbulent circulation related to cloud-top radiative cooling is not properly reproduced, advocating for the need to develop a parameterization for top-down convection to capture the turbulence-microphysics interplay at cloud top.