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

Abstract

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.

Mixed‐Phase Clouds and Precipitation in Southern Ocean Cyclones and Cloud Systems Observed Poleward of 64°S by Ship‐Based Cloud Radar and Lidar

“…The cold front associated with this cyclone, as with the previous Mawson cyclone, remained well to the north of the continent (not shown, see Vignon et al. [2021] for further details). Satellite images and thermodynamic data from later times indicate that this cyclone weakened as it propagated south‐eastward toward the coast, with cloud dissipating in a midlevel westerly flow on January 16 (not shown).…”

“…Following this characterization of the fine‐scale structure of mixed‐phase clouds and precipitation within cyclones adjacent to the Antarctic, the next step is to simulate these events in high‐resolution models. Although it is likely that models will have difficulty producing and maintaining SLW, we suspect that by appropriately tuning the microphysical schemes using MARCUS observations, we will be able to more accurately reproduce the clouds’ vertical structure, evolution, and phase partitioning (Vignon et al., 2021). Such a path to model improvement of Southern Ocean clouds could be informed by recent analyses of geostationary satellite imagery, which are capable of providing cloud macrophysical properties and information on subcloud phase beneath supercooled liquid cloud tops (e.g., Noh et al., 2019).…”

Predicting Frigid Mixed‐Phase Clouds for Pristine Coastal Antarctica

“…Good agreement between observations and model output was recently achieved by Vignon et al (2021) in regional model simulations with WRF for the Southern Ocean. They adjusted the Morrison microphysics scheme (Morrison et al, 2005) for reduced heterogeneous nucleation consistent with the INP observations of McCluskey et al (2018) and produced realistic cloud water amounts, while simulations with the unmodified parameterization show a deficit of cloud water.…”

Introducing CRYOWRF v1.0: Multiscale atmospheric flow simulations with advanced snow cover modelling

“…The model is initialized and forced at the lateral boundaries by ERA5 reanalysis data (Hersbach et al, 2020). The parameterizations used are: RRTMG (shortwave and longwave radiation), Kain-Fritsch (KF, convection), a modified version of the Morrison scheme that improves representation of secondary ice production (microphysics, Vignon et al, 2021;Sotiropoulou et al, 2021), and MYNN (boundary layer scheme). The simulation is nudged against ERA5 for wind speeds in zonal and meridional direction in the top 20 levels of the atmosphere.…”