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L. Li, A. P. Ingersoll (Division of Geological and Planetary Sciences,)
We use a reduced-gravity quasi-geostrophic model with a parameterization of moist convection that is based on Galileo and Cassini observations of lightning and convective storms (Little et al., 1999; Gierasch et al., 2000; Porco et al., 2003). The features of the jets we want to reproduce in the model include: (1) the curvature of the zonal jet profile, which violates the barotropic stability criterion near many of the westward jets (Ingersoll et al., 1981; Li et al., 2004), (2) the speed of the zonal jets, which is related to their width, given that the jets marginally violate the barotropic stability criterion, and (3) the sign of the eddy momentum flux, which is into the jets and tends to sustain them (Beebe et al., 1979; Ingersoll et al., 1981; Salyk et al., 2004). The features of moist convective storms that are taken from observation include: (1) the tendency of the storms to occur in the cyclonic belts, (2) the rapid divergence of horizontal velocity near the cloud tops, and (3) the lifetime of the storms, which is on average 4-5 days (Li et al., 2004). We find that moist convection leads to zonal jets in the upper layer, but the jets violate the barotropic stability criterion only if the flow in the deep underlying layer is westward. We can reproduce the chevron shape on the sides of the jets if we postulate that the clouds persist longer than the storms that produce them. We can reproduce the number and frequency of moist convection storms by assuming that they carry most of the planet¡¯s vertical heat flux (Gierasch et al., 2000). The NASA Planetary Atmospheres Program supported this research.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.