A potential vorticity perspective on the motion of a mid-latitude winter stormReport as inadecuate

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1 CNRM-GAME - Groupe d-étude de l-atmosphère météorologique 2 LMD - Laboratoire de Météorologie Dynamique

Abstract : 1 The motion of mid-latitude surface cyclones relative to the jet streams is of particular interest because of the com-monly observed strong and rapid deepening they undergo when they cross the upper-level jet axis. The purpose of the present study is to validate a recent theory that may explain this 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 ver-tically averaged potential vorticity PV gradient associated with the jet. To test this theoretical result, numerical sensi-tivity 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 analy-sis 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 upper-level jet axis. A PV-inversion tool is used to modify the vertically aver-aged PV gradient of the initial state. 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. The interpretation is that an enhanced PV gradient reinforces the dipolar PV anomaly located at upper levels which, in turn, advects the surface cyclone faster towards the jet axis. Citation: Rivière, G., P. Arbogast, G. Lapeyre, and K. Maynard 2012, A potential vorticity perspective on the motion of a mid-latitude winter storm,

Author: G. Rivière - P. Arbogast - G. Lapeyre - K. Maynard -

Source: https://hal.archives-ouvertes.fr/


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