Preprints
https://doi.org/10.5194/cp-2024-46
https://doi.org/10.5194/cp-2024-46
04 Jul 2024
 | 04 Jul 2024
Status: this preprint is currently under review for the journal CP.

Stretched polar vortex increases mid-latitude climate variability during the Last Glacial Maximum

Yurui Zhang, Hans Renssen, Heikki Seppä, Zhen Li, and Xingrui Li

Abstract. The Arctic stratospheric polar vortex (PV) is a key driver of winter weather, and has been found playing role in winter climate variability and its predictability in Eurasia and North America on inter-annual and decadal time scales. However, to what extent this relationship also plays a role in driving climate variability on glacial-interglacial time scales is still unknown. Here, by systematically analysing PV changes in four sets of PMIP4 simulations for the last glacial maximum (LGM) and the pre-industrial (PI), we explore how the PV changed during the glacial climate and how it influenced climate variability. Our results show that under LGM conditions, the PV stretched toward the Laurentide ice sheet, which resulted in a less stable ellipse shape that increased the possibility of cold air outbreaks into mid-latitudes. During the LGM, this stretched PV pushed cold Arctic air further equatorward, increasing winter climate variability over the more (southward) southern mid-latitudes. In particular, this strengthened winter cooling over the mid-latitudes beyond the coverage of the Laurentide ice sheet (unlike summer). PV-induced temperature variability also explains the inter-model spread, as removing the PV variation from the model results reduces the inter-model spread by up to 5 °C over mid-latitude Eurasia. These results highlight the critical role of PV in connecting the polar region and mid-latitudes on glacial-interglacial time scales. These connections are reminiscent of intra-seasonal stratosphere–troposphere coupling.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Yurui Zhang, Hans Renssen, Heikki Seppä, Zhen Li, and Xingrui Li

Status: open (until 29 Aug 2024)

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  • RC1: 'Comment on cp-2024-46', Anonymous Referee #1, 10 Jul 2024 reply
Yurui Zhang, Hans Renssen, Heikki Seppä, Zhen Li, and Xingrui Li
Yurui Zhang, Hans Renssen, Heikki Seppä, Zhen Li, and Xingrui Li

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Short summary
The upper and lower atmosphere are interacted. The polar regions, with a high-speed and cyclonically rotating winds, provide a window that the upper air flow affects the mid-latitudes' weather which results in intra-seasonal climate variability. To explore their impacts on glacial-interglacial cycles, we analysed climate model results, and found that the stretched upper air flow increases glacial climate variability via more cold air outbreaks, highlighting their connections on multi-timescales.