Air Moisture Climatology and Related Physical Processes in the Antarctic on the Basis of ERA5 Reanalysis

Atmospheric moisture is a key component in the water cycle and radiative transfer. In this study, a comprehensive picture of air moisture climatology and related physical processes is presented for the first time for the circumpolar area south of 50 degrees S. The results are based on the most modern global reanalysis, ERA5, which manages reasonably well to close the Antarctic water budget. We show that over the ocean transient cyclones have the dominant role in determining moisture conditions, whereas over the continent the moisture conditions are largely affected by the mean circulation. Over the open sea, moisture transport from lower latitudes is an equally important source of moisture compared to the local evaporation, but practically all precipitating moisture over the plateau is provided by the horizontal transport. Over the ocean and continental slopes, southward moisture transport brings warm and moist air masses from lower latitudes, notably increasing atmospheric water vapor and cloud water, and simultaneously decreasing local evaporation over the open sea. On the Antarctic plateau, radiative cooling leads to high relative humidity and causes condensation of moisture especially near the surface, causing a nearly permanent specific humidity inversion layer. As a consequence, dry air masses with extremely low specific humidity are formed. These dry air masses are transported downward from the plateau by katabatic winds, experiencing adiabatic warming. This leads to a decrease in relative humidity and to a downward-directed sensible heat flux, which enable efficient surface evaporation on the coastal slopes and farther over coastal polynyas and leads.