Recurrent Rossby waves and south-eastern Australian heatwaves

Abstract. In the Northern Hemisphere, recurrence of transient synoptic-scale Rossby wave packets in same phase over periods days to weeks, termed RRWPs, may repeatedly create similar surface weather conditions. This can lead persistent anomalies. Here, we first demonstrate significance RRWPs for hot spells Southern Hemisphere (SH) using ERA-Interim (ERA-I) reanalysis dataset and then examine role blocks heatwaves south-eastern Australia (SEA). A Weibull regression analysis shows that are statistically associated with a significant increase duration several regions SH, including SEA. Two case studies SEA summers 2004 2009 illustrate forming recurrent ridges (anticyclonic potential vorticity – PV anomalies), aiding persistence heatwaves. Then, weather-station-based identify heatwaves, find more frequent than climatology during extreme activity (high RSEA). On both high RSEA circumglobal zonal wavenumber 4 5 (WN4, WN5) anomaly patterns present composite mean upper-level field, an anticyclonic The Fourier decomposition meridional wind velocity fields further reveals WN4 WN5 components suitable aids ridge RSEA. addition, anomalous blocking Indian South Pacific oceans which help modulate RRWPs.