Joint modulations of Antarctic Oscillation and EL Niño-Southern Oscillation on extratropical cyclone activities in the Antarctica

Abstract Investigating the activities of extratropical cyclones and their relationships with atmospheric and oceanic climate indices is essential for understanding the broader dynamics of the atmosphere-ocean system over Antarctica. Based on an extratropical cyclone track dataset, we examine the joint modulation of Antarctic Oscillation (AAO) and El Niño-Southern Oscillation (Oceanic Niño Index, ONI) on extratropical cyclone activity in Antarctica. Extratropical cyclone activity is generally enhanced during both AAO+ & ONI- and AAO- & ONI- phases.We compare sea surface temperature, sea level pressure, geopotential height and wind fields based on atmospheric reanalysis datasets. The AAO phases modulate sea level pressure, westerly winds, and geopotential height, thereby strengthening or weakening atmospheric circulation. Different ONI phases shift the centers of these anomalies. Moreover, the AAO and ONI jointly influence wind shear, with positive Eady growth rate anomalies roughly associated with negative wind shear anomalies. These results provide insights into the dynamics of extratropical cyclone activities in Antarctica.