Young Et Al. 2002, Gravity Waves in Jupiter's Stratosphere 2. Observations

The temperatures in Jupiter's stratosphere, as measured by the Galileo Atmosphere Structure Instrument (ASI), show fluctuations that have been interpreted as gravity waves. We present a detailed description of these fluctuations, showing that they are not likely to be due to either measurement error or isotropic turbulence. These fluctuations share features with gravity waves observed in the terrestrial middle atmosphere, including the shape and amplitude of the power spectrum of temperature with respect to vertical wavenumber. Under the gravity wave interpretation, we calculate ranges of energy deposition and heat fluxes, place limits on the eddy Prandtl number, and compare predicted and observed eddy diffusion coefficients. We find that wave heating or cooling is likely to be important in Jupiter's upper stratosphere, that the Prandtl number lies between 1 and 4.4, and that diffusive filtering theory is a poor predictor of the eddy diffusion coefficient in Jupiter's atmosphere. 1. Introduction The Atmosphere Structure Instrument (ASI) on the Galileo probe measured densities and temperatures in Jupiter's stratosphere that vary on scales ranging from 50 km to the limit of the resolution (2-4 km/point). Temperature variations on scales less than a scale height have also been seen in stellar occultations (e.g., French and Gierasch 1974) and radio occultations (Lindel et al. 1981). Interpretations of these small-scale temperature variations include turbulence (Jokipii and Hubbard 1977), gravity waves (French and Gierasch 1974), or planetary-scale, longer-lived phenomena (Allison 1990, Friedson 1999). The characteristics of the temperature or density variations are the key to interpreting the data in terms of the underlying dynamics. The ASI data combines high vertical resolution with a large range of altitudes, permitting a more detailed examination of the statistics of Jupiter's stratosphere than previously possible. Stratospheric temperature and density fluctuations have also been reported in the middle atmospheres of Titan and the other giant planets (e.g., Cooray et al. 1998, Sicardy et al. 1985, Roques et al. 1994). The quantitative description of the thermal and density variations presented here will help with comparative planetology, by establishing whether temperature variations in the outer planets exhibit a " universal power spectrum, " as temperatures appear to do in the Earth's middle atmosphere (VanZandt 1982). We describe the ASI measurements and errors in Section 2. In Section 3, we present a statistical analysis of Jupiter's stratosphere, with interpretation. The results are discussed in Section 4, and our conclusions are summarized in Section 5. The Galileo …