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| Titel |
Structure and dynamical Evolution of the Greenland Tip Jet: ERA40 climatology |
| VerfasserIn |
K. Vaage, T. Spengler, H. C. Davies, R. S. Pickart |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250020827
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| Zusammenfassung |
| The Greenland tip jet is an intense, narrow and intermittent westerly wind phenomenon
southeast of Cape Farewell that often takes place in winter and plays an important role for
both the circulation and seasonal evolution of the mixed layer in the Irminger Sea below. The
orographically induced winds result from an interaction between a low pressure system and
the high topography of Greenland. Using the ERA-40 reanalysis data set and an air-parcel
trajectory model, we investigate the wintertime conditions in which tip jets occur and
describe their characteristics. A catalog of 586 objectively detected tip jet events for
the winters 1957-2002 reveal significant positive correlations of tip jet frequency
with both the NAO index and the latitude of the Icelandic Low. Composite tip jet
averages expose strong winds with peak velocities and heat fluxes of up to 30 m∕s and
600 W∕m2, respectively, sustained for less than one day. Backward trajectories
demonstrate a continental origin of the air parcels comprising the tip jet, and confirm that
acceleration through deflection around Greenland is a robust feature of most tip jets. A
vertical coherence between the lower-level tip jet and upper-level jet stream winds
along with strong positive anomalies of cyclone and jet stream residence in the
vicinity of Greenland may suggest that tip jets arise due to an interplay between the
high topography of Greenland and the presence of a cyclone to the east and the jet
stream to the south. We favor an alternative hypothesis that explains the co-location
of the tip jet and the jet stream with the tandem propagation of cyclones and the
upper-level steering currents in which they are embedded. In this scenario, which
is supported by a high variance in jet stream wind speed during tip jets, there is
not necessarily a direct dynamical link between the upper- and lower-level winds. |
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