Strong interaction between two co-rotating vortices in rotating and stratified flows.

Vortex-motion;Stratified flow;Gravity waves

Bambrey, Ross R. ; Reinaud, Jean Noel ; Reinaud, Jean Noel

University:University of St Andrews

Department:Mathematics & Statistics (School of)

关键词: Vortex-motion;    Stratified flow;    Gravity waves;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/341/thesis.pdf?sequence=1&isAllowed=y

来源: DR-NTU

【 摘 要 】

In this study we investigate the interactions between two co-rotating vortices.These vortices are subject to rapid rotation and stable stratification such asare found in planetary atmospheres and oceans. By conducting a large numberof simulations of vortex interactions, we intend to provide an overview of theinteractions that could occur in geophysical turbulence.We consider a wide parameter space covering the vortices height-to-widthaspect-ratios, their volume ratios and the vertical offset between them. The vorticesare initially separated in the horizontal so that they reside at an estimatedmargin of stability. The vortices are then allowed to evolve for a period of approximately20 vortex revolutions.We find that the most commonly observed interaction under the quasi-geostrophic(QG) regime is partial-merger, where only part of the smaller vortex is incorporatedinto the larger, stronger vortex. On the other hand, a large number of filamentaryand small scale structures are generated during the interaction. We findthat, despite the proliferation of small-scale structures, the self-induced vortex energyexhibits a mean `inverse-cascade' to larger scale structures. Interestingly weobserve a range of intermediate-scale structures that are preferentially shearedout during the interactions, leaving two vortex populations, one of large-scalevortices and one of small-scale vortices.We take a subset of the parameter space used for the QG study and performsimulations using a non-hydrostatic model. This system, free of the layer-wisetwo-dimensional constraints and geostrophic balance of the QG model, allows forthe generation of inertia-gravity waves and ageostrophic advection. The study ofthe interactions between two co-rotating, non-hydrostatic vortices is performedover four different Rossby numbers, two positive and two negative, allowing forthe comparison of cyclonic and anti-cyclonic interactions. It is found that agreater amount of wave-like activity is generated during the interactions in anticyclonicsituations. We also see distinct qualitative differences between the interactionsfor cyclonic and anti-cyclonic regimes.