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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.06.020 Byline: Katia I. Matcheva (a), Barney J. Conrath (a), Peter J. Gierasch (a), F. Michael Flasar (b) Keywords: Jupiter; Jupiter; atmosphere; Atmospheres; structure Abstract: We analyze the thermal infrared spectra of Jupiter obtained by the Cassini-CIRS instrument during the 2000 flyby to infer temperature and cloud density in the jovian stratosphere and upper troposphere. We use an inversion technique to derive zonal mean vertical profiles of cloud absorption coefficient and optical thickness from a narrow spectral window centered at 1392 cm.sup.-1 (7.18 [mu]m). At this wavenumber atmospheric absorption due to ammonia gas is very weak and uncertainties in the ammonia abundance do not impact the cloud retrieval results. For cloud-free conditions the atmospheric transmission is limited by the absorption of molecular hydrogen and methane. The gaseous optical depth of the atmosphere is of order unity at about 1200 mbar. This allows us to probe the structure of the atmosphere through a layer where ammonia cloud formation is expected. The results are presented as height vs latitude cross-sections of the zonal mean cloud optical depth and cloud absorption coefficient. The cloud optical depth and the cloud base pressure exhibit a significant variability with latitude. In regions with thin cloud cover (cloud optical depth less than 2), the cloud absorption coefficient peaks at 1.1[+ or -]0.05bar, whereas in regions with thick clouds the peak cloud absorption coefficient occurs in the vicinity of 900[+ or -]50 mbar. If the cloud optical depth is too large the location of the cloud peak cannot be identified. Based on theoretical expectations for the ammonia condensation pressure we conclude that the detected clouds are probably a system of two different cloud layers: a top ammonia ice layer at about 900 mbar covering only limited latitudes and a second, deeper layer at 1100 mbar, possibly made of ammonium hydrosulfide. Author Affiliation: (a) Department of Astronomy, Cornell University, Ithaca, NY 14853, USA (b) NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA Article History: Received 25 October 2004; Revised 24 April 2005

We analyze the thermal infrared spectra of Jupiter obtained by the Cassini-CIRS instrument during the 2000 flyby to infer temperature and cloud density in the jovian stratosphere and upper troposphere. We use an inversion technique to derive zonal mean vertical profiles of cloud absorption coefficient and optical thickness from a narrow spectral window centered at 1392 [cm.sup.-1] (7.18 [micro]m). At this wavenumber atmospheric absorption due to ammonia gas is very weak and uncertainties in the ammonia abundance do not impact the cloud retrieval results. For cloud-free conditions the atmospheric transmission is limited by the absorption of molecular hydrogen and methane. The gaseous optical depth of the atmosphere is of order unity at about 1200 mbar. This allows us to probe the structure of the atmosphere through a layer where ammonia cloud formation is expected. The results are presented as height vs latitude cross-sections of the zonal mean cloud optical depth and cloud absorption coefficient. The cloud optical depth and the cloud base pressure exhibit a significant variability with latitude. In regions with thin cloud cover (cloud optical depth less than 2), the cloud absorption coefficient peaks at 1.1 [+ or -] 0.05 bar, whereas in regions with thick clouds the peak cloud absorption coefficient occurs in the vicinity of 900 [+ or -] 50 mbar. If the cloud optical depth is too large the location of the cloud peak cannot be identified. Based on theoretical expectations for the ammonia condensation pressure we conclude that the detected clouds are probably a system of two different cloud layers: a top ammonia ice layer at about 900 mbar covering only limited latitudes and a second, deeper layer at 1100 mbar, possibly made of ammonium hydrosulfide. Keywords: Jupiter; Jupiter, atmosphere; Atmospheres, structure

The JO-ingress radio occultation of the Galileo orbiter by Jupiter exhibits a system of well-defined, regularly spaced electron layers in the altitude range where the presence of gravity waves have been previously inferred. Based on the terrestrial analog of sporadic E and spread F ionospheric layers, we argue that the observed layers are a result of dynamical processes rather than chemistry. We consider the impact of upward propagating gravity waves on the plasma distribution in a [H.sup.+] dominated ionosphere. The relevant physics is discussed and illustrated with an analytic, small-amplitude model. A time-dependent, 2D, large-amplitude model is developed to simulate the observed large excursions in the JO-electron density profile. We show that gravity waves with parameters consistent with the thermal structure of Jupiter's upper atmosphere are capable of creating large peaks in the electron density similar to the observed ones. The ionospheric response is extremely anisotropic with respect to the direction of wave propagation. We demonstrate that the location of the JO-ingress radio occultation on Jupiter favors large ionospheric response for waves propagating along the magnetic meridian. A wave driven plasma flux results in plasma removal above the altitude of maximum ionospheric response and plasma deposition in the region below, significantly modifying the initial steady state electron density profile. Key Words: Jupiter; ionosphere; dynamics; aeronomy; planets.

Heating Jupiter's thermosphere by viscous dissipation of upward propagating gravity waves is evaluated with correct formulations of total energy conservation and the total wave induced vertical energy flux. In contrast to the results of L. A. Young et al. (1997, Science 276, 108-111), our calculations, with their wave amplitudes and parameters, yield a maximum thermospheric temperature of T = 380 K at 552 km above the 1-bar level in comparison to the Galileo probe inferred temperature of T = 900 K and therefore gravity waves may not be solely responsible for the observed steep temperature gradient just above the homopause. The large sensible heat flux associated with dissipating gravity waves generates net heating of the lower regions and net cooling of the upper regions of wave dissipation due to energy redistribution. The transition from net heating to net cooling occurs at the level of constant wave amplitude. In regions of substantial wave dissipation the local cooling rate due to sensible heat flux divergence can exceed the local heating due to convergence of the Eliassen-Palm flux to produce (1) net cooling of and (2) a distinct temperature decrease ([approximately equal to]65 K) in the topside thermosphere. To simulate Jupiter's thermospheric temperature profile inferred from the Galileo probe data with (1) gravity wave heating only, (2) 100% conversion of wave energy to internal energy, and (3) radiative cooling by [Mathematical Expression Omitted] near-IR emission [approximately]0.1 erg [cm.sup.-2] [s.sup.-1], gravity waves must deposit their energy high in the thermosphere with peak heating occurring near [approximately]500 and [approximately]1000 km with near saturation amplitudes at very high altitudes (> 1100 km). Key Words: Jupiter, atmosphere; atmospheres, dynamics; planets.