Understanding Jupiter’s Polar Vortex Crystals

This thesis explores vortex dynamics on background planetary potential vorticity (PV) gradients caused by planetary rotation. Using a quasi-geostrophic (QG) pseudo-spectral model, we investigated the formation of opposing PV annuli that form on the vortex edges as a result of this drift known as a vortex shield which forms as a result of fluid becoming trapped in the vortex flow and carried to higher latitudes. We analyse the shield formation process and measure the effects of planetary and vortex parameters on the width and strength of these shields and we investigate the role of Rossby wave radiation on the long-term radial decay of the vortex core. We found ultimately that shield strength largely depends on the initial latitude and extent of meridional displacement, while the width of the shield is decided by the ratio of the vortex peak tangential velocity relative to its drift velocity. Therefore, for the shield width there is a strong dependence on both the background planetary PV gradient (or latitude of the beta-plane) and the deformation scale. We found that the vortex core decays in a quasi-linear fashion, with a strong dependence on both the background gradient and the deformation scale. Ultimately, it was found that planetary parameters that promote faster Rossby wave radiation lead to faster core decay rates. We derived an analytical model in order to explore the factors that affect the size of the vortex trapped-zone and to more precisely quantify the process of radial decay, allowing us to more accurately determine the timescales of decay for near-deformation scale shielded vortices. It was found that the trapped-zone (or shield width) largely scales similarly to the simulations, with the vortex peak velocity to drift speed ratio being the most important parameter in deciding the size of the vortex trapped-zone. We additionally found that the near-deformation scale vortices have relatively constant decay rates and thus we were able to reproduce the quasi-linear decay seen in the numerical simulations. For sub-deformation scale vortices, the decay rate is highly non-linear leading to the rapid decay of the vortex towards the barotropic limit. Finally, we investigated the role of the central cyclone on the precession direction and speed of the circling circumpolar cyclones in a Jovian-like vortex crystal. In particular we explored the role of the circumpolar cyclone rest position relative to the pole and its influence on speed of circumpolar cyclone precession. Ultimately, it was found that, regardless of planetary parameters and central cyclone configuration, the precession speeds and direction of the circumpolar cyclones are largely dependent on the position relative to the pole, suggesting that the observed drift speeds of the Jovian circumpolar cyclones are entirely explained by the simple point vortex dynamics induced by the competing combination of the beta-effect and the central cyclone winds.<p></p>

Author dc:creator

• Aaron Carruthers (21042074)

• Jupiter
• Juno
• Vortex
• Vortex Shielding
• QGPV
• Rossby Waves
• Vortex Decay
• Vortex Crystals
• Polar Vortex

Statement dc:rights

• All rights reserved
• Embargoed

Identifier

10779/exe.32311164.v1

OAI identifier oai:identifier

oai:figshare.com:article/32311164