Röthlisberger Matthias, Papritz Lukas
Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland.
Nat Geosci. 2023;16(3):210-216. doi: 10.1038/s41561-023-01126-1. Epub 2023 Feb 20.
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.
热浪是最致命的气候危害之一。然而，导致其近地表温度异常（𝑇'）的物理过程——来自气候较暖区域的空气平流、下沉空气中的绝热增温以及非绝热加热——的相对重要性仍存在争议。在这里，我们通过沿着气块向后轨迹评估𝑇'收支来量化这些过程的重要性。我们首先表明，2021年6月北美西部热浪期间极端的近地表𝑇'主要是由非绝热加热产生的，在较小程度上是由绝热增温产生的。通过系统地分解1979 - 2020年全球每年最热日（TX1day事件）期间的𝑇'，我们发现存在强烈的地理差异，平流在中纬度海洋占主导，绝热增温在山脉附近占主导，非绝热加热在热带和亚热带陆地上占主导。然而，在许多地区，TX1day事件是由这些过程共同作用产生的。在全球平均值中，TX1day异常沿着轨迹在大约60小时和1000公里的范围内形成，尽管存在很大的区域变异性。因此，本研究揭示了极端高温本质上的非局地和区域独特形成路径，量化了决定其强度的关键因素，并为气候模型关于极端高温的评估提供了新的定量方法。
