Using Numerical Simulation to Consider the Observed Variations in the Behavior and Appearance of Dark Spots on the Ice Giants

The most recent observation of a dark spot on Neptune (Simon et al., 2019) is the latest confirmation that these vortices are a not uncommon feature in the atmospheres of the Ice Giants. With observations of more than a half-dozen of these vortices since the Voyager II encounters, we are now in a position to start categorizing the nature of these features and try to determine what drives their different properties and behaviors. These behaviors can include latitudinal and longitudinal drift, shape oscillations, and the formation of companion clouds. Simulations of these dark spots with EPIC GCM (Dowling et al., 2006) can capture all of these behaviors, providing a diagnostic tool that can investigate the underlying physics of the observed phenomena. However, these simulations have generally targeted a specific feature such as the 1989 Great Dark Spot (GDS-89) or the Uranian Dark Spot (UDS), as opposed to developing a consistent understanding that captures the observed characteristics of all known dark spots. This more generalized work targets the effect of spot size, shape, and strength on its subsequent evolution, examining for example its interaction with the zonal wind shears to generate drift or a lack of drift or the existence of orographic uplift-driven condensation that may or may not generate companion clouds. This systematic simulation of multiple vortices and comparison of the results aims to reveal the key physics that govern the observed differences between the increasing number of recorded dark spots, creating stronger links between the simulations and future observations.