Patterns of low-frequency variability in a three-level quasi-geostrophic model. Climate dynamics 13(12):883–904 Dee DP, Uppala SM, Simmons AJ, Berrisford
Abstract. To assess the extent to which atmospheric low-frequency variability can be ascribed to internal dynam-ical causes, two extended runs (1200 winter seasons) of a three level quasi-geostrophic model have been carried out. In the Þrst experiment the model was forced by an average forcing Þeld...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
| Published: |
Springer
1997
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| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.514.4185 http://iri.columbia.edu/~alesall/pubslist/climdyn1997_cortietal.pdf |
| Summary: | Abstract. To assess the extent to which atmospheric low-frequency variability can be ascribed to internal dynam-ical causes, two extended runs (1200 winter seasons) of a three level quasi-geostrophic model have been carried out. In the Þrst experiment the model was forced by an average forcing Þeld computed from nine winter seasons; in the second experiment we used a periodically variable forcing in order to simulate a seasonal cycle. The analysis has been focused on the leading Northern Hemisphere teleconnection patterns, namely the PaciÞc North Ameri-can (PNA) and the North Atlantic Oscillation (NAO) patterns, and on blocking, both in the Euro-Atlantic and PaciÞc sectors. The NAO and PNA patterns are realisti-cally simulated by the model; the main di⁄erence with observations is a westward shift of the centres of action of the NAO. Related to this, the region of maximum fre-quency of Atlantic blocking is shifted from the eastern boundary of the North Atlantic to its central part. Apart from this shift, the statistics of blocking frequency and duration compare favourably with their observed counter-parts. In particular, the model exhibits a level of interan-nual and interdecadal variability in blocking frequency which is (at least) as large as the observed one, despite the absence of any variability in the atmospheric energy sour-ces and boundary conditions on such time scales. 1 |
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