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| Titel |
Isentropic tracking of lower-stratospheric potential vorticity anomalies: A 10-year winter climatology |
| VerfasserIn |
S. Kew, M. Sprenger |
| 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 |
250028107
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| Zusammenfassung |
| Isentropic charts exhibit many mesoscale potential vorticity (PV) maxima in the weak
background PV field of the lowermost stratosphere. Such PV anomalies are known to act as
precursors to cyclogenesis when in the vicinity of the tropopause. A feature-tracking tool
is developed and applied to ten consecutive winters of the European Centre for
Medium-range Weather Forecasts (ECMWF) Reanalysis (ERA-40) to establish the general
characteristics and life cycle of these anomalies and thus shed light on an earlier
phase of cyclogenesis. The tool identifies the anomalies as local maxima, whose
amplitudes are defined with respect to the surrounding local background PV. The
isentropic wind field is used to advect structures forward to the next time step,
thus predicting their subsequent position and form. A tracking is enabled when
there is a satisfactory overlap between the predicted and observed structures. The
routine detects the merger and splitting of PV entities as well as their genesis and
lysis.
The 10-year climatology reveals that the anomalies are frequently located near high
topography in a quasi-annular band at about 70-N, can be long-lived (days to weeks) and
their core PV is typically 2 PV units above that of their local surroundings. Clear life cycles
in along-track composites of amplitude, PV, shape (isotropy) and velocity indicate that the
anomalies have their own distinctive dynamics.
The tracking methodology is being adapted for cyclone tracking to take part in
the Intercomparison of Mid-Latitudinal Storm Diagnostics (IMILAST) project. |
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