The Typicality of Regimes Associated with Northern Hemisphere Heatwaves

TL;DR

This study identifies typical atmospheric regimes associated with Northern Hemisphere heatwaves, revealing their recurrent nature and potential for improved prediction and climate assessment.

Contribution

The paper introduces archetype analysis to characterize atmospheric patterns linked to heatwaves, highlighting their frequency and role in extreme temperature events.

Findings

Blocking high pressure systems are key to heatwave development.

Heatwave regimes are recurrent and typical of surface extremes.

Rossby Wave Packets influence the persistence of heatwaves.

Abstract

We study the hemispheric to continental scale regimes that lead to summertime heatwaves in the Northern Hemisphere. By using a powerful data mining methodology - archetype analysis - we identify characteristic spatial patterns consisting of a blocking high pressure systems embedded within a meandering upper atmosphere circulation that is longitudinally modulated by coherent Rossby Wave Packets. Periods when these atmospheric regimes are strongly expressed correspond to large increases in the likelihood of extreme surface temperature. Most strikingly, these regimes are shown to be typical of surface extremes and frequently reoccur. Three well publicised heatwaves are studied in detail - the June-July 2003 western European heatwave, the August 2010 "Russian" heatwave, and the June 2021 "Heatdome" event across western North America, and are shown to be driven by blocking high pressure systems linked to stalled Rossby Wave Packets. We discuss the implications of our work for long-range prediction or early warning, climate model assessment and post-event diagnosis.