Quantifying the physical processes leading to atmospheric hot extremes at a global scale

Area of Science:

• Climate Science
• Atmospheric Physics
• Extreme Weather Events

Background:

• Heat waves are a significant climate hazard with severe impacts.
• The specific physical drivers of near-surface temperature anomalies during heat waves (advection, adiabatic warming, diabatic heating) are debated.
• Understanding these drivers is crucial for predicting and mitigating heat wave impacts.

Purpose of the Study:

• To quantify the relative importance of physical processes contributing to extreme heat events.
• To identify geographical variations in the formation pathways of hot extremes.
• To provide a framework for evaluating climate models' representation of heat waves.

Main Methods:

• Analysis of the temperature anomaly budget using air-parcel backward trajectories.
• Decomposition of near-surface temperature anomalies (𝑇') during the hottest days of each year (TX1day events) globally from 1979-2020.
• Evaluation of advection, adiabatic warming, and diabatic heating contributions.

Main Results:

• Extreme heat in western North America (June 2021) was mainly driven by diabatic heating and adiabatic warming.
• Global analysis shows regional differences: advection dominates over mid-latitude oceans, adiabatic warming near mountains, and diabatic heating over tropical/subtropical land.
• TX1day events often result from a combination of these processes.
• Global mean formation trajectories span approximately 60 hours and 1,000 km.

Conclusions:

• Hot extremes have distinct, non-local formation pathways that vary by region.
• The study quantifies key factors influencing heat wave magnitude.
• Findings enable improved quantitative evaluation of climate models for hot extremes.