The Structure and Evolution of Heat Waves in Southeastern Australia

Abstract

The underlying large-scale dynamical processes responsible for the development of heat waves in Victoria, southeastern Australia, in summer are presented here. Heat waves are defined as periods of at least three days and two nights for which daily maximum and minimum temperatures exceed the 90th percentile for a particular location and month, using a station daily temperature dataset. Composites of upper-level potential vorticity anomalies from the Interim ECMWF Re-Analysis (ERA-Interim) reveal that heat waves in southeastern Australia are associated with propagating Rossby waves, which grow in amplitude and eventually overturn. The process of overturning generates an upper-level anticyclone over southern Australia and an upper-level trough to the northeast, with maximum amplitudes near the tropopause. The northerly flow associated with the circulation around the surface anticyclone advects hot air from the continental interior over the southeast of Australia, leading to extreme surface temperatures. Composite rainfall shows that precipitation is enhanced in the vicinity of the upper-level trough over northeastern Australia, consistent with adiabatically forced vertical motion, destabilization of the atmosphere, and modified moisture fluxes. Heat waves in the southeast are frequently accompanied by heavy rainfall over the northeast of the continent and adjacent ocean.

Modes of climate variability and heat waves in Victoria, southeastern Australia

“…This band of enhanced precipitation is also present on the first day of all heat waves in Victoria [Parker et al, 2014].…”

“…Anomalies are calculated as the deviation from the seasonal mean for these DJF months [see Parker et al, 2014]. (The results using a day-of-year mean instead of a seasonal mean are not appreciably different.…”

“…Anomalies are calculated as the deviation from the day-of-year mean calculated from the daily rainfall data [see Parker et al, 2014].…”

Relationships between climate variability, soil moisture, and Australian heatwaves

“…These sea level high-pressure systems are coupled with high-pressure anomalies aloft [e.g., Meehl and Tebaldi, 2004;Trigo et al, 2005;Dole et al, 2011] and are stationary for an extended number of days [e.g., Nairn and Fawcett, 2013]. Dynamical teleconnections of prevailing heatwave weather systems to tropical low-pressure systems and Rossby waves also exist [Parker et al, 2013[Parker et al, , 2014aBoschat et al, 2015] and may be more prevalent during particular modes of climate variability [Parker et al, 2014b]. Indeed, climate variability modes are another link in the heatwave development chain; however, with the exception of some focus over southeast Australia [Parker et al, 2014a[Parker et al, , 2014b, little research has been undertaken regarding continental-scale relationships between these phenomena and discrete heatwave characteristics.…”

A global perspective on atmospheric blocking using GPS radio occultation – one decade of observations

“…Due to this imbalance comparably few studies investigate blocking in the SH, mostly focusing on impacts in Australia and New Zealand (Australian-New Zealand blocking region) and in South America (south-eastern Pacific blocking region) (e.g. Marques and Rao, 1999;Cowan et al, 2013;Pook et al, 2013;Parker et al, 2014). Several studies have also looked into the influence of other phenomena like the El Niño-Southern Oscillation (ENSO) or the Antarctic oscillation (also known as Southern Annular Mode) on SH blocking (Damião Mendes and Cavalcanti, 2014;Oliveira et al, 2014).…”