Published July 21, 2025 | Version v6
Preprint Open

Ship-based lidar evaluation of Southern Ocean low clouds in the storm-resolving general circulation model ICON and the ERA5 and MERRA-2 reanalyses

Creators

  • 1. Department of Meteorology (MISU), Stockholm University, Stockholm, Sweden
  • 2. Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 3. School of Physical and Chemical Sciences, University of Canterbury, Christchurch, Aotearoa/New Zealand
  • 4. Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt am Main, Hesse, Germany
  • 5. Australian Antarctic Division, Kingston, Tasmania, Australia
  • 6. Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  • 7. Cooperative Institute of Severe and High Impact Weather Research and Operations, University of Oklahoma, Norman, OK, USA
  • 8. School of Meteorology, University of Oklahoma, Norman, OK, USA
  • 9. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 10. ROR icon National Snow and Ice Data Center
  • 11. Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, USA
  • 12. Department of Physics & Atmospheric Science, Dalhousie University, Halifax, Canada
  • 13. New South Wales Department of Planning and Environment, Sydney, New South Wales, Australia
  • 14. New Zealand Defence Force, Wellington, New Zealand

Description

Global storm resolving models (GSRMs) represent the next generation of global climate models. One of them is a 5-km Icosahedral Nonhydrostatic Weather and Climate Model (ICON). Its high resolution means that parameterizations of convection and clouds, including subgrid-scale clouds, are omitted, relying on explicit simulation but necessarily utilizing microphysics and turbulence parameterizations. Standard-resolution (10–100 km) models, which use convection and cloud parameterizations, have substantial cloud biases over the Southern Ocean (SO), adversely affecting radiation and sea surface temperature. The SO is dominated by low clouds, which cannot be observed accurately from space due to overlapping clouds, attenuation, and ground clutter. We evaluated SO clouds in ICON and the ERA5 and MERRA-2 reanalyses using approximately 2400 days of lidar observations and 2300 radiosonde profiles from 31 voyages and a Macquarie Island station during 2010–2021, compared to the models using a ground-based lidar simulator. We found that ICON and the reanalyses underestimate the total cloud fraction by about 10 and 20%, respectively. ICON and ERA5 overestimate the cloud occurrence peak at about 500 m, associated with underestimated lower tropospheric stability and overestimated lifting condensation level. The reanalyses strongly underestimate fog and very low-level clouds, and MERRA-2 underestimates cloud occurrence at almost all heights. Outgoing shortwave radiation is overestimated in MERRA-2, implying a “too few, too bright” cloud problem. SO cloud and fog biases are a substantial issue in the analyzed models and result in shortwave and longwave radiation biases.

In review in Journal of Geophysical Research: Atmospheres.

Files

Kuma et al. (2025), Ship-based lidar evaluation of Southern Ocean low clouds in the storm-resolving general circulation model ICON and the ERA5 and MERRA-2 reanalyses (in review 2025-07-21).pdf

Files (19.6 MB)

Additional details

Funding

European Commission
NextGEMS - Next Generation Earth Modelling Systems 101003470
European Commission
CleanCloud - Clouds and climate transitioning to post-fossil aerosol regime 101137639
Wenner-Gren Foundations
Swedish e-Science Research Centre
United States Department of Energy
DE-SC0021159