期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：38
DOI：10.1073/pnas.2200890119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Extreme midlatitude weather is strongly associated with the unusual meandering of jets. A central question is whether it is caused by or related to global warming. Here, we show that zonally asymmetric thermal forcing can drive a dramatic shift in planetary-scale atmospheric motion. As the zonal mean flow is reduced, a small-amplitude response confined near the surface shifts to a large-amplitude response reaching the upper atmosphere. As the high latitudes warm more rapidly under global warming, the reduction in zonal mean wind strength can trigger wavier atmospheric jets.
Recent studies have argued that global warming is responsible for a wavier jet stream, thereby driving midlatitude extreme flooding and drought. Polar amplification—the relative enhancement of high-latitude temperatures under global warming—is argued to be the principal climate state driving midlatitude extremes. Namely, the decreased meridional temperature gradient suppresses the mean zonal winds, leading to wavier midlatitude jets. However, although observations are consistent with such a linkage, a detailed dynamical mechanism is still debated. Here, we argue that the Northern Hemisphere land–sea thermal forcing contrast that underlies zonally asymmetric forcing drives a response in the planetary geostrophic motion, which provides balanced mean fields for synoptic eddies in midlatitudes and thus for wavier jet streams. We show that when the barotropic zonal mean wind
U is smaller than a threshold, proportional to the
β-plane effect and dry static stability, the flow field exhibits a dramatic transition from a response confined near the surface to one reaching the upper atmosphere. As global warming enhances polar amplification, the midlatitude jet stream intensity is suppressed. The confluence of these effects leads to wavier jet streams.
