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| Titel |
A potential vorticity perspective on the motion of mid-latitude surface cyclones: the example of the winter storm Xynthia |
| VerfasserIn |
Gwendal Rivière, Philippe Arbogast, Guillaume Lapeyre, Karine Maynard |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077084
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| Zusammenfassung |
| Mid-latitude surface cyclones are commonly observed to move across the mean flow from the equator to the pole and to undergo a strong and rapid deepening when they cross the axis of the large-scale jet stream. The purpose of the present study is to validate a recent theory that may explain this cross-jet motion which is a generalization of the so-called beta drift in the mid-latitude baroclinic context. According to this theory, the key parameter controlling the movement of a surface cyclone across the mean tropospheric jet is the vertical-average potential vorticity (PV) gradient associated with the jet. To test this theoretical result, numerical sensitivity experiments are performed using the Météo-France global operational forecast model ARPEGE-IFS for the particular case of the storm Xynthia (26–28 February 2010). The control forecast, starting from the operational analysis almost 2 days before the storm hit France, represents the trajectory of the storm quite well, together with the deepening during the crossing of the large-scale upper-level jet axis. A PV-inversion tool is used to modify the vertical-average PV gradient at the initial time. As expected from the theory, when the PV gradient is intensified, there is a quicker displacement of the surface cyclone toward the jet axis and the jet-crossing phase occurs earlier than in the control forecast. The opposite occurs for a reduced PV gradient. A dynamical interpretation is provided in terms of upper-levels PV anomalies generated by Rossby wave radiation. |
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