Deformation and destruction of north-eastward drifting dipoles

• Published in: Physics of fluids (1994) 2023-11, Vol.35 (11)
• Main Authors: Davies, J., Sutyrin, G. G., Crowe, M. N., Berloff, P. S.
• Format: Article
• Language: English
• Subjects: Dipoles; Evolution; Fluid dynamics; Mathematical models; Physics; Planetary waves
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/5.0171909

We systematically study the evolution of Larichev–Reznik dipoles in an equivalent-barotropic quasi-geostrophic beta-plane model in high-resolution numerical simulations. Our results shed light on the self-organization and rich dynamics of dipolar vortices, which are ubiquitous in geophysical flows. By varying both dipole strength and initial angle α0 of dipole tilt to the zonal direction, we discover new breakdown mechanisms of the dipole evolution. The dipoles are quickly destroyed by Rossby wave radiation, if initial tilt is too large or the dipole is too weak; otherwise, via damped oscillations, the dipoles tend to adjust themselves to different states drifting eastward. Two competing physical mechanisms that govern dipole transformations are found: (1) spontaneous dipole instability due to a growing critical linear mode and (2) meridional separation of dipole partners that accumulates over the adjustment period and prevents the above instability. Which mechanism prevails depends on the initial tilt and dipole strength, and the details of this are discussed.