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Please join us for this Climate Coffee with Matthias Röthlisberger on Quantifying the physical processes leading to atmospheric hot extremes at a global scale

Abstract

Heat waves are among the deadliest climate hazards. Yet the relative importance of the physical processes causing their near-surface temperature anomalies (𝑇′)—advection of air from climatologically warmer regions, adiabatic warming in subsiding air and diabatic heating—is still a matter of debate. Here we quantify the importance of these processes by evaluating the 𝑇′ budget along air-parcel backward trajectories. We first show that the extreme near-surface 𝑇′ during the June 2021 heat wave in western North America was produced primarily by diabatic heating and, to a smaller extent, by adiabatic warming. Systematically decomposing 𝑇′ during the hottest days of each year (TX1day events) in 1979–2020 globally, we find strong geographical variations with a dominance of advection over mid-latitude oceans, adiabatic warming near mountain ranges and diabatic heating over tropical and subtropical land masses. In many regions, however, TX1day events arise from a combination of these processes. In the global mean, TX1day anomalies form along trajectories over roughly 60 h and 1,000 km, although with large regional variability. This study thus reveals inherently non-local and regionally distinct formation pathways of hot extremes, quantifies the crucial factors determining their magnitude and enables new quantitative ways of climate model evaluation regarding hot extremes.

Röthlisberger, M., Papritz, L. Quantifying the physical processes leading to atmospheric hot extremes at a global scale. Nat. Geosci. 16, 210–216 (2023). https://doi.org/10.1038/s41561-023-01126-1

About Matthias

Matthias Röthlisberger is a senior scientist at ETH Zürich, Switzerland. Matthias’ work focusses on identifying and quantifying the meteorological causes of weather and climate extremes, as well as on their representations in climate models.

Matthias obtained his PhD in Climate Science from the University of Bern, Switzerland, where he investigated how the dynamics of synoptic-scale Rossby waves modulates the occurrence, persistence and intensity of surface weather extremes. After his PhD, Matthias joined the Atmospheric Dynamics group at ETH Zürich as a PostDoc to investigate the meteorological causes of entire extreme seasons, such as extremely hot summers, wet spring seasons or stormy winters.

In his current work, Matthias combines Lagrangian and Eulerian diagnostics applied to reanalysis data and climate model output to quantify the physical processes leading to temperature extremes, to investigate which factors determine exceptionally intense heat waves, and to evaluate climate models regarding their ability to realistically simulate such events from a physical and meteorological point of view.

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