What Drives Dark Spot Drift?

Dark spots on the Ice Giants have exhibited a variety of drifting motions ranging from meridional drift across more than ten degrees of latitude to oscillatory drift in both longitude and latitude to no significant drift at all. While the Kida vortex provides a simple two-dimensional dark spot model, it does not explain drift motions. The possibility of background potential vorticity gradients, created by planetary rotation and zonal wind variations, to generate drifting vortices has been demonstrated in numerical simulations but results have been inconsistent when compared to observed dark spot motions. Further, the inclusion or exclusion of different phenomena in the simulations, such as clouds, has been shown to alter the drift characteristics. Thus, quantifying the underlying mechanisms that drive vortex drift remains elusive.

A possible approach to gaining insight into these motions is to parametrically examine the outcomes of simulations, allowing the search for differences in the flow physics to indicate key mechanisms. This approach is applied to a series of dark spot simulations of varying vortex strength, size, background conditions, and drift rates, serving as a preliminary examination of how these parameters influence dark spot drift.