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The Resonant Interaction of a Tropical Cyclone and a Tropopause Front in a Barotropic Model. Part II: Frontal Waves

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  • 1 Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • | 2 British Atmospheric Data Centre, Rutherford Appleton Laboratory, Chilton, United Kingdom
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Abstract

The influence of frontal waves on the interaction of a tropical cyclone and a tropopause front is investigated in an idealized framework. In a nondivergent barotropic model the front is represented by a vorticity step with a superimposed sinusoidal perturbation. This gives rise to a jet that meanders to the north and south and can be viewed as a sequence of upper-level troughs and ridges. The model evolution depends sensitively on the position of the cyclone relative to the troughs and ridges. Here a bifurcation point is identified that is located on the trough axis at a distance where the zonal speed of the background flow equals the phase speed of the wave. Arbitrarily small displacements from this position determine whether a cyclone is advected toward the front or repelled. Only a limited range of wavelengths can lead to track bifurcations. The largest effects are obtained for resonant frontal waves propagating with a phase speed matching the initial zonal translation speed of the cyclone. Weak and large-scale vortices can be disrupted when approaching the bifurcation point, where they are exposed to continuously strong shear deformation.

Corresponding author address: Leonhard Scheck, Karlsruher Institut für Technologie, Institut für Meteorologie und Klimaforschung, Kaiserstr. 12, 76131 Karlsruhe, Germany. Email: leonhard.scheck@kit.edu

Abstract

The influence of frontal waves on the interaction of a tropical cyclone and a tropopause front is investigated in an idealized framework. In a nondivergent barotropic model the front is represented by a vorticity step with a superimposed sinusoidal perturbation. This gives rise to a jet that meanders to the north and south and can be viewed as a sequence of upper-level troughs and ridges. The model evolution depends sensitively on the position of the cyclone relative to the troughs and ridges. Here a bifurcation point is identified that is located on the trough axis at a distance where the zonal speed of the background flow equals the phase speed of the wave. Arbitrarily small displacements from this position determine whether a cyclone is advected toward the front or repelled. Only a limited range of wavelengths can lead to track bifurcations. The largest effects are obtained for resonant frontal waves propagating with a phase speed matching the initial zonal translation speed of the cyclone. Weak and large-scale vortices can be disrupted when approaching the bifurcation point, where they are exposed to continuously strong shear deformation.

Corresponding author address: Leonhard Scheck, Karlsruher Institut für Technologie, Institut für Meteorologie und Klimaforschung, Kaiserstr. 12, 76131 Karlsruhe, Germany. Email: leonhard.scheck@kit.edu

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