Tropical Cyclones and strong MJO events as precursors of summertime Antarctic atmospheric rivers

Abstract

Antarctic atmospheric rivers (ARs) are rare but high-impact events that have a major influence on the surface mass and energy balance of the ice sheet, by causing strong positive anomalies in temperature and precipitation. Previous studies have shown that the main moisture sources of Antarctic ARs extend from the midlatitudes to the subtropics (equatorward of 30° latitude). Here, we focus on the tropical moisture origins through analyzing tropical cyclones and the Madden-Julian Oscillation, i.e. the most intense tropical convective events. They can act in some cases as precursors of the AR development particularly during the austral summer season, increasing the Antarctic AR probability by a factor of 3–5. Not all intense tropical convective events produce ARs: a precise phase locking between regions of poleward moisture export and extratropical Rossby waves is necessary to channel tropical moisture poleward, and form an AR over the Southern Ocean reaching the Antarctic ice sheet.