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

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.