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The different stratospheric influence on cold-extremes in Eurasia and North America

Kretschmer, Marlene and Cohen, Judah and Matthias, Vivien and Runge, Jakob and Coumou, Dim (2018) The different stratospheric influence on cold-extremes in Eurasia and North America. npj Climate and Atmospheric Science, 1 (1), p. 44. Springer. ISSN 2397-3722

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Official URL: http://www.nature.com/articles/s41612-018-0054-4

Abstract

The stratospheric polar vortex can influence the tropospheric circulation and thereby winter weather in the mid-latitudes. Weak vortex states, often associated with sudden stratospheric warmings (SSW), have been shown to increase the risk of cold-spells especially over Eurasia, but its role for North American winters is less clear. Using cluster analysis, we show that there are two dominant patterns of increased polar cap heights in the lower stratosphere. Both patterns represent a weak polar vortex but they are associated with different wave mechanisms and different regional tropospheric impacts. The first pattern is zonally symmetric and associated with absorbed upward-propagating wave activity, leading to a negative phase of the North Atlantic Oscillation (NAO) and cold-air outbreaks over northern Eurasia. This coupling mechanism is well-documented in the literature and is consistent with the downward migration of the northern annular mode (NAM). The second pattern is zonally asymmetric and linked to downward reflected planetary waves over Canada followed by a negative phase of the Western Pacific Oscillation (WPO) and cold-spells in Central Canada and the Great Lakes region. Causal effect network (CEN) analyses confirm the atmospheric pathways associated with this asymmetric pattern. Moreover, our findings suggest the reflective mechanism to be sensitive to the exact region of upward wave-activity fluxes and to be state-dependent on the strength of the vortex. Identifying the causal pathways that operate on weekly to monthly timescales can pave the way for improved sub-seasonal to seasonal forecasting of cold spells in the mid-latitudes.

Item URL in elib:https://elib.dlr.de/126426/
Document Type:Article
Title:The different stratospheric influence on cold-extremes in Eurasia and North America
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Kretschmer, MarleneUNSPECIFIEDUNSPECIFIED
Cohen, JudahUNSPECIFIEDUNSPECIFIED
Matthias, VivienUNSPECIFIEDUNSPECIFIED
Runge, JakobInstitute of Data Sciencehttps://orcid.org/0000-0002-0629-1772
Coumou, DimUNSPECIFIEDUNSPECIFIED
Date:2018
Journal or Publication Title:npj Climate and Atmospheric Science
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In SCOPUS:No
In ISI Web of Science:No
Volume:1
Page Range:p. 44
Publisher:Springer
ISSN:2397-3722
Status:Published
Keywords:Atmospheric dynamics,Climate change
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:other
DLR - Research area:Raumfahrt
DLR - Program:R - no assignment
DLR - Research theme (Project):R - no assignment
Location: Jena
Institutes and Institutions:Institute of Data Science
Deposited By: Runge, Jakob
Deposited On:08 Feb 2019 08:17
Last Modified:08 Feb 2019 08:17

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