Linking ENSO to Synoptic Weather Systems in Eastern Australia

Abstract

El Niño-Southern Oscillation (ENSO) is the main driver of interannual east Australian rainfall variability, but its link with rain-producing synoptic weather systems is unclear. By tracking low pressure systems in ERA5 over 1979 to 2021, we find that springtime cyclones are linked to variations in the large-scale atmospheric circulation during ENSO events. On spring days with a cyclone during La Niña, a pressure dipole occurs with a strong anticyclonic anomaly southeast of Australia and a cyclonic anomaly over eastern Australia. The northeasterly circulation directs tropical moisture toward eastern Australia, and coupled with induced ascent, promotes rainfall in this region. Both dynamical and thermodynamical changes are important for the rainfall response. An almost opposite circulation response occurs on cyclone days during El Niño events: high-pressure over the Australian continent reduces rainfall in eastern Australia. These synoptic setups resemble the seasonal-mean Rossby wave teleconnections, indicating a link between weather systems and ENSO.