Abstract A catastrophic heatwave struck North America (NA) in the summer of 2021, the underlying cause of which currently remains unclear. The reanalysis data (1980–2021) is analyzed to elucidate the mechanism modulating the summer heatwaves. We find the heatwaves over western NA tend to occur concurrently with quasi-barotropic ridges (QBTRs). The 2021 record-breaking heatwave, in particular, coincides with an extended eight-day QBTR event. The frequency of QBTRs is modulated by large-scale forcing. During the period of 1980–2000, it is correlated with the Arctic Oscillation. After 2000, however, the QBTR frequency is highly associated with sea ice variations. Specifically, the negative sea ice anomalies in the Chukchi Sea are usually associated with stronger net surface shortwave radiation and low cloud cover, triggering upward motion and a low-pressure center in the low- and mid-troposphere. The low pressure strengthens a stationary wave response, concomitant with two alternately high- and low-pressure centers, inducing more frequent QBTRs over western NA. These findings indicate that further Arctic sea ice loss under a warming climate will likely lead to more devastating heatwaves over western NA.
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Increased Summer European Heatwaves in Recent Decades: Contributions From Greenhouse Gases‐Induced Warming and Atlantic Multidecadal Oscillation‐Like Variations
Summer heatwaves over Europe, which can cause many deaths and severe damage, have become increasingly frequent over central and eastern Europe and western Russia in recent decades. In this paper, we estimate the contributions of the warming due to increased greenhouse gases (GHG) and nonlinear variations correlated with the Atlantic Multidecadal Oscillation (AMO) to the observed heatwave trend over Europe during 1980–2021, when the GHG‐induced warming over Europe exhibits a linear trend. It is found that GHG‐induced warming contributes to ∼57% of the European heatwave trend over 1980–2021, while the cold‐to‐warm phase shift of the AMO‐like variations accounts for ∼43% of the trend via the intensification of midlatitude North Atlantic jet. The recent trend of heatwaves over western and northern Europe is mainly due to GHG‐induced warming, while that over central and eastern Europe and western Russia is primarily related to the combined effect of the AMO‐like variations and GHG‐induced warming. To some extent, GHG‐induced warming is an amplifier of the increasing trend of recent AMO‐related European heatwaves. Moreover, European blocking (Ural blocking, UB) is shown to contribute to 55% (42%) of the AMO‐related heatwave trend via the influence of midlatitude North Atlantic jet. In the presence of a strong North Atlantic jet during the recent warm AMO phase, UB events concurrent with positive‐phase North Atlantic Oscillation can cause intense, persistent and widespread heatwaves over Europe such as that observed in the summer of 2022.
more » « less- PAR ID:
- 10513467
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Earth's Future
- Volume:
- 11
- Issue:
- 8
- ISSN:
- 2328-4277
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2023EF003701
