02 Jan 2023
02 Jan 2023
Status: this preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).

On the persistence of warm and cold spells in the Northern Hemisphere extratropics: regionalisation, synoptic-scale dynamics, and temperature budget

Alexandre Tuel1 and Olivia Martius1,2 Alexandre Tuel and Olivia Martius
  • 1Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Switzerland
  • 2Mobiliar Lab for Natural Risks, University of Bern, Switzerland

Abstract. Persistent warm and cold spells are often high-impact events that may lead to significant increases in mortality and crop damage, and can put substantial pressure on the power grid. Their spatial extent is seldom taken into account, or only based on case studies. Yet, the spatial dependence in prolonged warm or cold anomalies is critical to correctly understand the associated risks, whether in present-day or future climates. Here, we present a regionalisation of 3-week warm and cold spells in winter and summer across the Northern Hemisphere based on their sensitivity to the large-scale circulation. We identify spatially coherent regions and discuss the physical drivers responsible for persistent extreme temperature anomalies. Blocks are important precursors of such events – co-localized blocks for persistent summer warm spells and upstream blocks for winter cold spells. Recurrent Rossby wave patterns are also relevant for many mid-latitude regions. Additionally, summer warm spells are – unsurprisingly – often accompanied by negative precipitation anomalies that likely play an important role through land-atmosphere feedbacks.

Alexandre Tuel and Olivia Martius

Status: open (until 28 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1478', Anonymous Referee #1, 30 Jan 2023 reply
  • RC2: 'Comment on egusphere-2022-1478', Anonymous Referee #2, 02 Feb 2023 reply

Alexandre Tuel and Olivia Martius

Alexandre Tuel and Olivia Martius


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Short summary
Warm and cold spells often have damaging consequences for agriculture, power demand, human health or infrastructure, especially when they occur over large areas and persist for a week or more. Here, we split the Northern Hemisphere extra-tropics into coherent regions where 3-week warm and cold spells in winter and summer are associated with the same large-scale circulation patterns. To understand their physical drivers, we analyse the associated circulation and temperature budget anomalies.