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

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Journal of Geophysical Research Atmospheres
• Year: 2025
• Date: 2025-11-21
• Authors: Peter Kuma, Frida A.‐M. Bender, Adrian McDonald, Simon P. Alexander, Greg M. McFarquhar, John J. Cassano, Graeme Plank, Sean Hartery, Simon Parsons, Sally Garrett, Alex Schuddeboom, Anna Possner
• DOI: 10.1029/2024jd043145

Research Groups

This study evaluated Southern Ocean (SO) clouds in the 5-kilometer ICON model and ERA5/MERRA-2 reanalyses against extensive lidar and radiosonde observations, revealing that ICON and reanalyses significantly underestimate total cloud fraction and exhibit biases in cloud occurrence and radiation, particularly for low-level clouds and fog.

Objective

• To evaluate Southern Ocean cloud representation in the 5-kilometer Icosahedral Nonhydrostatic Weather and Climate Model (ICON) and the ERA5 and MERRA-2 reanalyses using ground-based lidar and radiosonde observations.

Study Configuration

• Spatial Scale: Global (for models), Southern Ocean (for evaluation region).
• Temporal Scale: 2010–2021 (for observations), approximately 2400 days of lidar observations and 2300 radiosonde profiles.

Methodology and Data

• Models used: Icosahedral Nonhydrostatic Weather and Climate Model (ICON) at 5-kilometer resolution, ERA5 reanalysis, MERRA-2 reanalysis.
• Data sources: Ground-based lidar observations (approximately 2400 days), radiosonde profiles (approximately 2300) from 31 voyages and Macquarie Island station, ground-based lidar simulator.

Main Results

• ICON and the reanalyses underestimate the total cloud fraction by approximately 10% and 20%, respectively, over the Southern Ocean.
• ICON and ERA5 overestimate the cloud occurrence peak at approximately 500 meters, associated with underestimated lower tropospheric stability and overestimated lifting condensation level.
• The reanalyses strongly underestimate fog and very low-level clouds.
• MERRA-2 underestimates cloud occurrence at almost all heights and overestimates outgoing shortwave radiation, implying a "too few, too bright" cloud problem.
• Southern Ocean cloud and fog biases are a substantial issue in the analyzed model and reanalyses, resulting in shortwave and longwave radiation biases.

Contributions

• Provides a comprehensive evaluation of Southern Ocean clouds in a next-generation global storm-resolving model (ICON) and two prominent reanalyses (ERA5, MERRA-2) using extensive ground-based lidar and radiosonde observations.
• Quantifies specific biases in cloud fraction, vertical distribution, and radiation for low-level clouds and fog, highlighting persistent issues even in high-resolution models.
• Identifies potential causes for cloud biases, such as underestimated lower tropospheric stability and overestimated lifting condensation level.

Funding

Citation

@article{Kuma2025ShipBased,
  author = {Kuma, Peter and Bender, Frida A.‐M. and McDonald, Adrian and Alexander, Simon P. and McFarquhar, Greg M. and Cassano, John J. and Plank, Graeme and Hartery, Sean and Parsons, Simon and Garrett, Sally and Schuddeboom, Alex and Possner, Anna},
  title = {Ship‐Based Lidar Evaluation of Southern Ocean Low Clouds in the Storm‐Resolving General Circulation Model ICON and the ERA5 and MERRA‐2 Reanalyses},
  journal = {Journal of Geophysical Research Atmospheres},
  year = {2025},
  doi = {10.1029/2024jd043145},
  url = {https://doi.org/10.1029/2024jd043145}
}