Non-Linear Aspects of a Barotropically Unstable Polar Vortex in a Forced-Dissipative System

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  • 強制-散逸系における順圧不安定な極渦の非線形な様相
  • 流れ場のレジームと物質輸送
  • Flow Régimes and Tracer Transport

Abstract

Non-linear dynamics of a barotropically unstable circumpolar vortex in a forced-dissipative system is investigated numerically with a high-resolution barotropic model on a spherical domain. Horizontal transport and mixing processes of a passive tracer are also investigated for several types of evolving flow fields with a high-resolution transport model.<br>Vacillating and irregular solutions are obtained within some parameter ranges as well as steady-wave solutions. In the vacillation, planetary waves propagate eastward, changing the horizontal structure periodically. Stepwise transitions from steady-wave solutions to irregular ones via vacillations are found for a sech-type jet which is unstable mainly on the poleward flank of the jet, while no irregular solutions are obtained for a tank-type jet which is unstable on the equatorward flank of the jet within realistic parameter ranges of the stratosphere.<br>Time evolutions of an ideal passive tracer field show that the edge of the circumpolar vortex is so robust that mixing through the edge hardly occurs whether the solution is steady or not. Exceptionally intermittent intrusion and ejection of fluid through the vortex edge occur in the irregular solutions for the sech-type jet.

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