Extreme heat events from an object viewpoint with application to south‐east Australia

Abstract

Surface high temperature extremes have a large impact on society and environment, and their relationship to the large‐scale circulation has been explored in detail. However, most of these studies have investigated these relationships in a single location or region, and focused on events that persist at this location sufficiently long to be considered heatwave‐like events. Moreover, few studies have explored the full lifecycle of extreme temperature events. The present study introduces a simple object that can be used to follow areas of extreme temperature that moves through time, and presents a basic global climatology of these objects, showing that shorter high temperature objects are more frequently found in the tropics and longer objects are more likely along the mid‐latitude jet regions. Heatwave‐length (three or more days) high temperature events in the south‐eastern part of Australia are also explored using this object approach, showing that while many shorter length objects in the area form and decay within the region, longer objects tend to first appear along the coast west of much of the south‐east Australian region and decay mostly over the ocean to the south‐east of the region. The area affected by the objects is closely associated to the propagation of circulation anomalies, moving from west to east with surface temperature extremes slightly to the west of upper‐level anticyclonic anomalies and in between a surface high to the east and a trough/low/cold front to the west. The large‐scale circulation anomalies are similar in structure but differ in magnitude for different lengths of objects that affect south‐east Australia, although longer‐lived objects have upper‐level anticyclonic anomalies located further north than the shorter heatwave‐length objects. Objects that affect both far western and south‐eastern Australia closely resemble the longer south‐eastern Australian heatwave‐length objects.

Interactive influence of ENSO and IOD on contiguous heatwaves in Australia

“…Vogel et al (2020) investigated projections of large contiguous heatwaves globally by considering neighbouring countries as contiguous regions and found that they will substantially increase under the RCP8.5 emissions scenario. Over Australia, King and Reeder (2021) tracked spatially contiguous extreme heat events (not necessarily heatwaves) in the southeast during 1979-2018 to explore their lifecycle. However, contiguous heatwaves have not yet been a research focus of Australian heatwaves.…”

Anthropogenic forcing has increased the risk of longer-traveling and slower-moving large contiguous heatwaves

“…2C). The predominant southeastward-moving heatwaves in Australia are possibly linked to a slow-moving transient anticyclone, which is accompanied by northwesterly flow over the southeast of Australia ( 28 , 29 ). For contiguous heatwaves in South America, their northeastward movements are likely associated with the jet stream that transports warm air from the inland regions toward the coasts and further northeastward ( 30 ).…”

The life cycle of the heatwave boundary layer identified from commercial aircraft observations at Melbourne Airport (Australia)

“…The final step is to identify heatwave days. To ensure there is a sufficiently large number of heatwave days in the composite means (Sections 3.2-3.4), and following the work of King and Reeder (2021), heatwaves in Melbourne for December-March (DJFM) 2003-2018 are defined as periods of at least 3 consecutive days for which the daily maximum temperature is above the 80th percentile of daily maximum temperatures at Melbourne station. The calculation of percentiles uses a 15-day window around the day of year on data from 1979 onwards.…”