EPIC Modeling of Seasonal Thermal Forcing on Uranus

Details EPIC Modeling of Seasonal Thermal Forcing on Uranus EPIC Modeling of Seasonal Thermal Forcing on Uranus

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.5505s&link_type=abstract

American Astronomical Society, DPS meeting #39, #55.05; Bulletin of the American Astronomical Society, Vol. 39, p.526

Astronomy and Astrophysics

Astronomy

Scientific paper

Uranus is unique among the giant planets in that its measured temperature is quite close to its equilibrium temperature. This implies a relatively large role for solar insolation in the energy budget of the planet's observable weather layer. When combined with Uranus' extreme axial tilt, the seasonal variation of atmospheric dynamics is expected to be significant. Several observations in the IR and radio support this expectation as Uranus approaches equinox, including altered zonal winds, increased cloud activity, and strengthening molecular gradients (e.g. Hammel et al., (2005), Icarus 175, 534-545; Hofstadter and Butler, (2003), Icarus 184, 170-180).
However, little modeling of seasonal change on Uranus has been performed in the past twenty years. We present ongoing modifications to the EPIC general climate model (Dowling et al. (2006) Icarus 182, 259-273). In addition to dynamical updates to the Uranus model, we are implementing a thermal forcing term within the upper few bars of Uranus' atmosphere. This forcing term varies seasonally across latitudes to simulate the role of solar insolation. Heat deposition for each layer is determined using an exponentially decreasing transmission function with depth; sunlight that is not transmitted by a given layer is absorbed within it. The transmission function can be made to correspond to physically meaningful depths such as the expected location of the stratospheric hydrocarbon haze and the tropospheric methane cloud.
We will conduct spin-up experiments of planetary winds initially at rest, using solar insolation as the only forcing term to reproduce Uranus' observed zonal wind profile. We further expect to simulate seasonal zonal wind variability similar to that seen in observations.
This work was supported by NASA through grant number NNG05GB45G.

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