The evolution of surface quasi-geostrophic modons on sloping topography

This work discusses modons, or dipolar vortices, propagating along sloping topography. Two different regimes exist, which are studied separately using the surface quasi-geostrophic equations. First, when the modon propagates in the direction opposite to topographic Rossby waves, steady solutions exi...

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Bibliographic Details
Published in:Journal of fluid mechanics 2023-08, Vol.970, Article A10
Main Authors: Crowe, Matthew N., Johnson, Edward R.
Format: Article
Language:English
Subjects:
Analytical methods
Chlorophyll
Decay
Dipoles
Direction
JFM Papers
Planetary waves
Topography
Vortices
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Summary:This work discusses modons, or dipolar vortices, propagating along sloping topography. Two different regimes exist, which are studied separately using the surface quasi-geostrophic equations. First, when the modon propagates in the direction opposite to topographic Rossby waves, steady solutions exist and a semi-analytical method is presented for calculating these solutions. Second, when the modon propagates in the same direction as the Rossby waves, a wave wake is generated. This wake removes energy from the modon, causing it to decay slowly. Asymptotic predictions are presented for this decay and found to agree closely with numerical simulations. Over long times, decaying vortices are found to break down due to an asymmetry resulting from the generation of waves inside the vortex. A monopolar vortex moving along a wall is shown to behave in a similar way to a dipole, though the presence of the wall is found to stabilise the vortex and prevent the long-time breakdown. The problem is equivalent mathematically to a dipolar vortex moving along a density front, hence our results apply directly to this case.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2023.607