Seasonal Change on Uranus: GCM Modeling of Solar Insolation

Mike Sussman

Given Uranus' extreme axial tilt and the relative importance of solar insolation to the planetary energy balance, seasonal variation of atmospheric dynamics is expected to be significant. As Uranus' December 2007 equinox approaches, the current epoch presents the first time the Uranian equinox can be observed with AO-enabled and space telescopes, allowing for well-resolved imaging of seasonal phenomena. Observations have already been made demonstrating significant changes in the weather layer (e.g. Hammel et al., 2005) when compared with Voyager-era images, including the first-ever observation of a large vortex on Uranus similar to the Great Dark Spots seen on Neptune (News Release STScI-2006-47).

While prior simulations provide compelling clues to the planet's seasonal variability and its interplay with internal heat flux (Friedson and Ingersoll, 1987), efforts to model Uranian seasons have remained sparse since the time of Voyager. In an effort to explore such variability, I propose modifications to the EPIC general climate model (Dowling et al., 2006) to simulate dynamical phenomenon in the Uranian atmosphere. I will incorporate solar insolation, a term generally neglected in giant planet simulations, in a series of increasingly physical schemes as a forcing mechanism to drive seasonal variation. I will model atmospheric spin-up of the planet's zonal winds from rest. Additionally, I will attempt to drive Hadley-like meridional circulation as suggested by radio observations, and study vortex stability in a potentially variable zonal wind field.