Strong interaction between two co-rotating vortices in rotating and stratified flows.
Abstract
In this study we investigate the interactions between two co-rotating vortices.
These vortices are subject to rapid rotation and stable stratification such as
are found in planetary atmospheres and oceans. By conducting a large number
of simulations of vortex interactions, we intend to provide an overview of the
interactions that could occur in geophysical turbulence.
We consider a wide parameter space covering the vortices height-to-width
aspect-ratios, their volume ratios and the vertical offset between them. The vortices
are initially separated in the horizontal so that they reside at an estimated
margin of stability. The vortices are then allowed to evolve for a period of approximately
20 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 incorporated
into the larger, stronger vortex. On the other hand, a large number of filamentary
and small scale structures are generated during the interaction. We find
that, despite the proliferation of small-scale structures, the self-induced vortex energy
exhibits a mean `inverse-cascade' to larger scale structures. Interestingly we
observe a range of intermediate-scale structures that are preferentially sheared
out during the interactions, leaving two vortex populations, one of large-scale
vortices and one of small-scale vortices.
We take a subset of the parameter space used for the QG study and perform
simulations using a non-hydrostatic model. This system, free of the layer-wise
two-dimensional constraints and geostrophic balance of the QG model, allows for
the generation of inertia-gravity waves and ageostrophic advection. The study of
the interactions between two co-rotating, non-hydrostatic vortices is performed
over four different Rossby numbers, two positive and two negative, allowing for
the comparison of cyclonic and anti-cyclonic interactions. It is found that a
greater amount of wave-like activity is generated during the interactions in anticyclonic
situations. We also see distinct qualitative differences between the interactions
for cyclonic and anti-cyclonic regimes.
Type
Thesis, PhD Doctor of Philosophy
Rights
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http://creativecommons.org/licenses/by-nc-nd/3.0/
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