The vision of Uranus as a featureless planet has been proven increasingly anachronistic as the planet approaches its equinox. Uranus is notable for its unique 98 degree axial tilt, which leads to dramatic seasonal changes in its atmosphere. Currently, the northern hemisphere of Uranus is nearing its spring which happens once every 42 Earth years. Among the recent observations is the discovery of the first observed dark spot in August, 2006. This region of darker albedo was observed at about 27oN latitude and measured approximately 1700 by 3000 kilometers. Unfortunately, the first observations of this feature were limited to two days, meaning that its longer term behavior or even existence is not known.

Based on the observational results and the expectation of further near-term observations of Uranus, we present computational fluid dynamic simulations of the Uranian atmosphere. The Explicit Planetary Isentropic-Coordinate General Circulation Model of Dowling et al. (2006) is used to perform the simulations, guided by previous simulations of spots on the other jovian planets. The spot is treated as a vortex feature with an assumed wind distribution. The background conditions are based on observations, with several northern zonal wind profiles applied as part of a parametric study. Through the parametric simulations, we examine the sustainability of a dark spot on Uranus and possible dynamical explanations of why dark spots were previously observed on Neptune multiple times but not on Uranus until 2006. Investigation of local background vorticity in the region of the observed spot suggests that seasonal changes in the zonal wind profile may be a critical factor in the emergence of large sustained vortices on Uranus. The simulation results are also presented as a potential predictive tool for the future dynamics of the dark spot while hopefully awaiting further observations of the changing face of Uranus.