Intra-seasonal variability of extreme boreal stratospheric polar vortex events and their precursors

The dynamical variability of the boreal stratospheric polar vortex has been usually analysed considering the extended winter as a whole or only focusing on December, January and February. Yet recent studies have found intra-seasonal differences in the boreal stratospheric dynamics. In this study, th...

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Bibliographic Details
Published in:Climate dynamics 2017-11, Vol.49 (9-10), p.3473-3491
Main Authors: Díaz-Durán, Adelaida, Serrano, Encarna, Ayarzagüena, Blanca, Abalos, Marta, de la Cámara, Alvaro
Format: Article
Language:English
Subjects:
Anomalies
Atmospheric pressure
Climatology
Dynamics
Earth and Environmental Science
Earth Sciences
El Nino phenomena
Geophysics/Geodesy
La Nina
Northern Hemisphere
Observations
Oceanography
Polar vortex
Quasi-biennial oscillation
Seasonal variability
Seasonal variation
Seasonal variations
Stratosphere
Stratospheric circulation
Stratospheric dynamics
Stratospheric polar vortexes
Vortices
Wavelengths
Winter
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Summary:The dynamical variability of the boreal stratospheric polar vortex has been usually analysed considering the extended winter as a whole or only focusing on December, January and February. Yet recent studies have found intra-seasonal differences in the boreal stratospheric dynamics. In this study, the intra-seasonal variability of anomalous wave activity preceding polar vortex extremes in the Northern Hemisphere is examined using ERA-Interim reanalysis data. Weak (WPV) and strong (SPV) polar vortex events are grouped into early, mid- or late winter sub-periods depending on the onset date. Overall, the strongest (weakest) wave-activity anomalies preceding polar vortex extremes are found in mid- (early) winter. Most of WPV (SPV) events in early winter occur under the influence of east (west) phase of the Quasi-Biennial Oscillation (QBO) and an enhancement (inhibition) of wavenumber-1 wave activity (WN1). Mid- and late winter WPV events are preceded by a strong vortex and an enhancement of WN1 and WN2, but the spatial structure of the anomalous wave activity and the phase of the QBO are different. Prior to mid-winter WPVs the enhancement of WN2 is related to the predominance of La Niña and linked to blockings over Siberia. Mid-winter SPV events show a negative phase of the Pacific-North America pattern that inhibits WN1 injected into the stratosphere. This study suggests that dynamical features preceding extreme polar vortex events in mid-winter should not be generalized to other winter sub-periods.
ISSN:0930-7575
1432-0894
DOI:10.1007/s00382-017-3524-1