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| Titel |
Frequency of synoptic-scale winter storms over western North America: decadal variability arising from the Pacific Decadal Oscillation |
| VerfasserIn |
Tim Kruschke, Gregor C. Leckebusch, Dominik Renggli, Uwe Ulbrich |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053573
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| Zusammenfassung |
| Windstorms of synoptic scale, often related to extratropical cyclones, are meteorological
phenomena of great importance also from a socio-economic perspective. Due to political,
economic and social plans on the time scale of decades, a growing demand for reliable
climate projections on the decadal scale has emerged. A basic requirement for this kind of
medium-range climate projections is a better understanding of natural processes leading to
variabilities on this time scale. A crucial role for these questions is played by the
ocean-atmosphere interactions.
This study addresses the natural variability of winter storm frequency (wsf ) over western
North America (WNA) on decadal time scales by the means of a 506-year pre-industrial
control run of the ECHAM5/MPI-OM1 AOGCM. Regarding a possible oceanic influence, the
most important mode of variability in the Pacific, i.e. the Pacific Decadal Oscillation (PDO)
has to be considered.
Distinct variability of WNA-wsf on all time scales is evident, while spectrum analysis
reveals the decadal contribution to the total variance from interannual and lower
frequencies to be in the order of 10-20%. After band pass filtering to eliminate other
than decadal variabilities, principal component analysis of model SSTs yields the
PDO as the first EOF, explaining 28.6% of the total decadal North Pacific SST
variance.
It can be shown that WNA-wsf is significantly influenced by the PDO on decadal time scales
experiencing increased (decreased) wsf during positive (negative) phases of the PDO.
However, it has to be considered that this influence is sensitive to changes in the oceanic
current system.
There is a significant overall correlation of 0.52 between the PDO times series and the
decadal variability of WNA-wsf. Running 35y-correlations reveal that this connection is even
stronger for great sub-periods within the model simulation, except for two distinct phases of
approximately 50 years with almost no correlation.
The difference between the state of strong correlation between PDO and WNA-wsf and the
state of weak correlation is to be found within the ocean, i.e. in the appearence of the PDO
itself. During the phase of weak correlation compared to the usual state, the SST-anomalies of
the Kuroshio Extension proceed further north and east into the Bering Sea and towards the
Gulf of Alaska, which is assumed to be related to a stronger Kuroshio-Oyashio current
system. |
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