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F. M. Flasar, A. A. Simon-Miller (GSFC), B. J. Conrath (Cornell), G. S. Orton, B. Fisher (JPL)
The stratospheric temperatures retrieved from Cassini CIRS spectra obtained during the Jupiter swingby in January 2001 exhibit a hemispheric asymmetry. At the 4-mbar level the temperatures in the north are 5-10 K warmer than those at comparable latitudes in the south. Although the swingby occurred 8 months after N. summer solstice, the radiative relaxation times are large enough that one would have expected a phase lag of nearly a season (~3 years) in the temperature response. To examine this problem, we consider the scaling of a quasi-geostrophic flow with a zonal-mean meridional circulation forced by some unspecified wave/eddy zonal-momentum flux convergence. This mechanical forcing is unknown, but it could, for instance, be related in part to the waves driving the measured 4-year equatorial oscillation. We use the CIRS temperatures and those retrieved from Voyager IRIS and ground-based observations to constrain the temporal and spatial variations of the stratospheric temperatures. We find to lowest order that temporal variations in the stratospheric temperature result from the adiabatic heating and cooling associated with vertical motions. Radiative effects are secondary. For meridional circulations with a horizontal scale comparable to the planetary radius, the Coriolis torques associated with the meridional motions balance the wave/eddy zonal-momentum flux convergence. The simple set of equations allows one to solve for the flux convergence explicitly in terms of the measured stratospheric temperatures and their temporal variations and vertical gradients.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.