Southern Ocean precipitation: Toward a process‐level understanding

Large differences continue to exist between current precipitation products over the Southern Ocean (SO). This limits our ability to close the hydrological cycle over the SO and Antarctica, as well as limiting our understanding of a range of climatological and meteorological processes. This uncertainty arises from the absence of long‐term, high‐quality surface observational records of precipitation suitable for evaluation across a range of temporal and spatial scales. We have no “truth” for precipitation across this region that covers ~15% of the Earth's surface. These differences extend to spatial and temporal distributions and trends. Precipitation products that have been calibrated and evaluated against established observations in the Northern Hemisphere potentially may be biased due to fundamental differences in the dynamics and microphysics over the remote SO. This review first considers recent advances in our understanding of the precipitation of the SO, including spatial and temporal variability, thermodynamic phase, and response to climate drivers. We then examine several commonly used precipitation products derived from satellite observations (both passive and active), reanalyses, and merged products. Where possible, we examine the skill of these products across a range of precipitation processes that commonly occur across the SO. Finally, we look briefly at the potential of new resources, such as dual‐polarized radars and maritime disdrometers, that can be used in field campaigns specifically designed to observe precipitation at the process level, and ultimately used to evaluate precipitation products over the SO.