Quantifying the complex interplay behind heat waves

The complex interplay behind great heat
2021 Pacific Northwest heat-wave anomaly decomposition. a–d,T′ (a), advective T′ (b), adiabatic T′ (c) and diabatic T′ (d) averaged for 28–30 June 2021. eThe trajectories of air parcels arriving at Lytton (121.5° W, 50.0° N, marked with a black cross in a–e) during the same period. Trajectories are plotted only for trajectory times after the respective anomaly genesis (for trajectory times t for which tg ≤ t) and are colored according to their respective T′ (t). fFormation pathway of T′, averaged for all trajectories arriving within the heat-wave region during 28–30 June 2021. Gray shading (left y axis) denotes the fraction of trajectories for which tg ≤ t for each trajectory time t. Colored lines show the evolution of T′, advective T′, adiabatic T′ and diabatic T′ within these trajectories in Kelvin (right y axis). In each trajectory, all terms are set to zero for trajectory times before the respective tg. Credit: Nature Geoscience (2023). DOI: 10.1038/s41561-023-01126-1

Unusually hot weather in India and Pakistan at the end of March; a long, warmer-than-average summer in central Europe; extreme December temperatures in northern Argentina, Uruguay and Paraguay: 2022 was definitely a year of heat waves. And there is currently a broad consensus among climate researchers that such extreme events will occur much more frequently in the future than they do today.

There are essentially three mechanisms that cause the thermometer to climb to unusually high values: air from warmer regions reaches cooler ones, for example from the Sahara to central Europe; the air in a high-pressure area sinks, warming up in the process due to compression; or the sun heats the ground with unusual intensity, so that the air above it is warmed up more than normal.

Which process dominates?

“These three processes are easy to understand and can be described well with physical formulas,” explains Matthias Röthlisberger, a scientist in the Atmospheric Dynamics Group at ETH Zurich. So he finds it all the more remarkable that there is still intense controversy surrounding the three. Indeed, experts disagree on the importance of each of these three processes and on which one ultimately determines whether or not a heat wave occurs in a given location.

This is not simply an academic question, Röthlisberger says, “It’s important to understand how big a role each of these mechanisms plays. Because that’s instrumental for assessing how reliable the climate model projections are.” Granted, these accurately predict the frequency and duration of heat waves under current conditions. “But we don’t yet understand well enough whether or not these models are representing heat waves correctly for the right physical reasons.”

Extensive dataset

Röthlisberger now wants to close this knowledge gap together with his colleague Lukas Papritz from the same group. To address this contentious issue, the researchers analyzed heat extremes around the world, starting with a heat wave in Canada that measured temperatures of nearly 50 degrees Celsius in late June 2021.

For their analysis, the scientists used the latest dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF), which contains three-dimensional global weather data at high temporal and spatial resolution. From this extensive dataset, they first filtered out the hottest day in each of the past 40 years at every location in the world. Next, they meticulously calculated the path taken by the air near the ground at each location over the preceding 15 days and the last point at which this air had had a normal temperature.

The path of the air is crucial, because it points to the main mechanism of heating. If the air originates from a region with a then heat transport is a major contributor to the heat wave. If, instead, the air comes from a climatically comparable region, then the other two factors must be the cause of anomalous temperatures.

Substantial regional differences

Röthlisberger and Papritz examined a total of 250 million air parcels for their study. An evaluation of the data shows that how the three factors interact varies extremely from region to region. Each of the factors dominates in certain regions of the world, but very often heat waves result from a complex interplay of all three mechanisms.

In the case of the Canadian heat wave mentioned above, for example, the researchers were able to show that all three factors had a hand in the unusual weather situation. There are also within this single heat wave: in zones near the coast, it was primarily heat transport from the south and the sinking of the air that led to great heat, while further inland the extreme temperatures were a result of the dry and therefore heated ground warming the air.

For central Europe, meanwhile, the researchers find that hot Saharan air often has only an indirect influence. When hot air from Africa reaches Europe, rather than displacing the cooler air on the ground, it usually glides over it. “So the Saharan air ends up warming not the lower layers of the atmosphere but the middle and upper layers,” Papritz says. “In contrast, the hot air at ground level here mostly comes to us from the Atlantic and is then warmed up by the heated ground and compression.”

Nevertheless, air from the Sahara does play a significant role: by heating up the higher layers, it prevents the thunderstorms that would normally develop in response to the warming near the ground, and would go on to provide urgently hoped-for cooling.

The study is published in the journal Nature Geoscience.

More information:Matthias Röthlisberger, Quantifying the physical processes leading to atmospheric hot extremes at a global scale, Nature Geoscience (2023). DOI: 10.1038/s41561-023-01126-1. www.nature.com/articles/s41561-023-01126-1

Citation:Quantifying the complex interplay behind heat waves (2023, February 20)retrieved 1 March 2023from https://phys.org/news/2023-02-quantifying-complex-interplay.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Note: This article have been indexed to our site. We do not claim legitimacy, ownership or copyright of any of the content above. To see the article at original source Click Here

Related Posts
Fibril activity may be key to a better understanding of foot-and-mouth disease thumbnail

Fibril activity may be key to a better understanding of foot-and-mouth disease

Credit: CC0 Public Domain The imaging of vanishingly tiny structures created by the foot-and-mouth disease virus could one day help scientists develop new treatments for infected animals. In a new study published today, biologists from Leeds in collaboration with colleagues at the MRC-University of Glasgow Centre for Virus Research observed the interaction between components of…
Read More
Long March 7A rocket deploys two Chinese tech demo satellites thumbnail

Long March 7A rocket deploys two Chinese tech demo satellites

A Long March 7A rocket lifts off Dec. 23 from the Wenchang space center. Credit: CASCChina launched two classified Shiyan satellites Dec. 23 into a geostationary transfer orbit aboard a Long March 7A rocket, one of the country’s newest launch vehicles. The mission took off from China’s Wenchang launch base on Hainan Island. The 199-foot-tall…
Read More
CALB 40GWh LFP Battery Expansion and Targets 500 GWh by 2025 thumbnail

CALB 40GWh LFP Battery Expansion and Targets 500 GWh by 2025

China Lithium Battery Technology (CALB) has started building the thrid phase of an LFP lithium battery factory with manufacturing capacity of 40GWh and supporting assembly lines for battery modules and battery packs. For the first stage, CALB plans to invest 5 billion yuan ($786.275 million) in 10GWh manufacturing facilities. The first phase will output a…
Read More
Why do some babies grow poorly in the womb? thumbnail

Why do some babies grow poorly in the womb?

The mammalian fetus is dependent upon the placenta for nutrients and oxygen. The placenta is a specialized organ that contains cells from both baby and mother. Between 10% and 15% of babies grow poorly in the womb, often showing reduced growth of blood vessels in the placenta. In humans, these blood vessels expand dramatically between…
Read More
How to Inspire Your Team to Achieve Better Results thumbnail

How to Inspire Your Team to Achieve Better Results

Everyone’s needs are highly subjective. That fact does little to help you devise a one-and-done strategy for inspiring your team to achieve better results, but that’s okay.If you’re a leader who prioritizes success and wants to achieve the best results for you, your team, and your organization, then you’re willing to employ several strategies to…
Read More
Index Of News
Consider making some contribution to keep us going. We are donation based team who works to bring the best content to the readers. Every donation matters.
Donate Now

Subscription Form

Liking our Index Of News so far? Would you like to subscribe to receive news updates daily?

Total
0
Share