Madden-Julian Oscillation teleconnections to Australian springtime temperature extremes and their prediction in ACCESS-S1

Madden-Julian Oscillation teleconnections to Australian springtime temperature extremes and their prediction in ACCESS-S1

We examine impacts of the Madden–Julian Oscillation (MJO) on Australian springtime temperatures and extremes, explore the mechanisms behind the teleconnections, and assess their prediction in retrospective forecasts using the Bureau of Meteorology’s ACCESS-S1 dynamical forecast system. The MJO incites strong and significant warming across southern Australia in phases 2, 3 and 4 when its active convection propagates over the Indian Ocean and Maritime Continent. The heat signal appears strongest in south-eastern Australia during MJO phases 2 and 3 in the vicinity of a deep anticyclonic anomaly which brings warmer airflow to south-western Australia while promoting shortwave radiative heating in the southeast. This occurs as part of a Rossby wave train that emanates from the Indian Ocean and disperses across the Southern Hemisphere along a great circle route towards South America, in response to MJO convective heating on the equator. Importantly, we show the wave train emerges from the divergent outflow from anomalous MJO convection, rather than from the Rossby waves that exist within the MJO's baroclinic structure. Feedbacks between transient eddies and the low frequency flow to the south of Australia and southeast of South America reinforce the wave train in phases 1–3 but act against it during its demise in phase 4. The MJO is a source of subseasonal predictability of springtime heat and cold events over southern Australia in ACCESS-S1 at lead times of 2–4 weeks, yet there remains room for improvement in the model's depiction of the MJO and its teleconnection to the Southern Hemisphere.