Biases in Southern Ocean Precipitation From Shallow Convection: The Role of Cloud Morphology

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Abstract
Precipitation from marine boundary layer clouds is a critical yet highly uncertain feature of post‐frontal conditions over the Southern Ocean (SO), where shallow convection dominates. This study evaluates whether satellite retrievals (GPM‐IMERG and CloudSat) and reanalysis (ERA5) represent the contrasting precipitation between open and closed mesoscale cellular convection (MCC) observed over the SO, from limited in situ records. Substantial discrepancies are found across data sets. While ERA5 captures the expected contrast, GPM‐IMERG underestimates precipitation, especially from open MCCs, and fails to reflect morphological distinction. Both CloudSat products detect higher mean precipitation for open MCCs, though with differences in intensity distribution. Using observed precipitation rates and occurrence frequencies, open MCCs are estimated to contribute 9%–13% and closed MCCs 1%–11% of the annual precipitation between 40°S and 50°S. These results highlight the importance of improving the representation of marine atmospheric boundary layer cloud morphologies in models and observational data sets to better constrain the SO water cycle.

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