Do split and displacement sudden stratospheric warmings have different annular mode signatures?

Sudden stratospheric warmings (SSWs) contribute to intraseasonal tropospheric forecasting skill due to their surface impacts. Recent studies suggest these impacts depend upon whether the polar vortex splits or is displaced during the SSW. We analyze the annular mode signatures of SSWs in a 1000 year...

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Bibliographic Details
Published in:Geophysical research letters 2015-12, Vol.42 (24), p.10,943-10,951
Main Authors: Maycock, Amanda C., Hitchcock, Peter
Format: Article
Language:English
Subjects:
Algorithms
Annular
annular modes
Anomalies
Classification
climate variability
Coupling
Displacement
Meteorology
Signatures
Stratosphere
stratosphere‐troposphere coupling
stratospheric sudden warmings
Stratospheric warming
Troposphere
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Summary:Sudden stratospheric warmings (SSWs) contribute to intraseasonal tropospheric forecasting skill due to their surface impacts. Recent studies suggest these impacts depend upon whether the polar vortex splits or is displaced during the SSW. We analyze the annular mode signatures of SSWs in a 1000 year IPSL‐CM5A‐LR simulation. Although small differences in the mean surface Northern Annular Mode (NAM) index following splits and displacements are found, the sign is not consistent for two independent SSW algorithms, and over 50 events are required to distinguish the responses. We use the wintertime correlation between extratropical lower stratospheric wind anomalies and the surface NAM index as a metric for two‐way stratosphere‐troposphere coupling and find that the differences between splits and displacements, and between classification methodologies, can be simply understood in terms of their mean stratospheric wind anomalies. Predictability studies should therefore focus on understanding the factors that determine the persistence of these anomalies following SSWs. Key Points Large uncertainties exist in estimating differences in split/displacement impacts in reanalyses Differences in annular mode responses to split and displacement SSWs are not robust across definitions The tropospheric impact of SSWs is strongly related to their persistence in the lower stratosphere
ISSN:0094-8276
1944-8007
DOI:10.1002/2015GL066754