Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p31a1242s&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P31A-1242
Other
[5704] Planetary Sciences: Fluid Planets / Atmospheres, [6293] Planetary Sciences: Solar System Objects / Uranus
Scientific paper
Uranus' emitted infrared irradiance is only 6% more than its absorbed insolation, thus unlike other giant planets, Uranus appears to emit little internal heat. This results in an important role for solar radiation in the planetary energy budget in spite of its large heliocentric distance. Furthermore, its extreme axial tilt of 97 degrees generates a strongly varying insolation pattern which may act as a forcing mechanism to drive seasonal circulation effects. Some evidence such as increased discrete cloud features and altered zonal wind structure suggests seasonal change has already been observed (Hammel et al., 2005, Icarus 175, 534-545). Additionally, latent heat released from ortho-para hydrogen conversion is expected to be a significant source of atmospheric forcing for Uranus because the relative internal energy difference between the two states of hydrogen approaches its maximum value for the cold (~60 K) temperatures found in the planet's tropopause. To model potential seasonal changes and ortho-para conversion effects on Uranus' circulation, we employ the use of the Explicit Planetary Isentropic Coordinate (EPIC) GCM (Dowling et al., 2006, Icarus 182, 259-273), previously used successfully for simulations of atmospheric circulation for the other giant planets. Latent heat released by ortho-para conversion is already an existing feature of the EPIC codebase. To properly model the effects of seasonal insolation patterns, we replace EPIC's default Newtonian cooling with a new, more realistic two-color (visible and mid-IR) fully radiative scheme which properly models radiative diffusion. Our radiative scheme generally reproduces the planet's temperature-pressure profile with only three free parameters: extinction coefficients for visible radiation and mid-IR radiation, and an assumed abyssal temperature. We present the results of our modeling efforts, showing spin-up of zonal and meridional winds with forcing from various seasonal insolation patterns. We also demonstrate the effects upon atmospheric circulation of latent heat released from ortho-para conversion and its response to seasonal forcing.
Chanover Nancy
Dowling Timothy E.
Sussman Michael
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