Intra-seasonal variability of extreme boreal stratospheric polar vortex events and their precursors
Díaz-Durán, A; Serrano, E; Ayarzagüena, B; et al.Abalos, M; de la Cámara, A
Date: 20 January 2017
Journal
Climate Dynamics
Publisher
Springer Verlag
Publisher DOI
Abstract
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 ...
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
20 (QBO) and an enhancement (inhibition) of wavenumber-1 wave activity (WN1). Mid- and late winter WPV
21 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.
Mathematics and Statistics
Faculty of Environment, Science and Economy
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