Variations in Precipitation across the Southern Ocean

Abstract

The Southern Ocean lies beneath a unique region of the global atmosphere with minimal effects of land masses on the zonal flow. The absence of land masses also means that in situ observations of precipitation are limited to a few ocean islands. Two reanalyses and two satellite-based gridded datasets are analysed to estimate the character of the distribution of precipitation across the region. The latitudinal variation is computed across three longitudinal sectors, representing the Pacific, Atlantic and Indian Oceans. The most recent ECMWF reanalysis (ERA5) is found to produce the most accurate estimate of the mean profile and seasonal cycle of precipitation. However, there is little consistency in the estimates of trends in monthly anomalies of precipitation. Amore consistent description of precipitation trends is found by using linear regression of the precipitation anomaly with the local mean sea-level pressure anomaly, the Southern Annular Mode and the Southern Oscillation Index. In broad terms, precipitation is found to be decreasing at lower latitudes and increasing at higher latitudes which is consistent with earlier climate model simulations on the impacts of anthropogenic climate change.