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Abstract: We report here the first detection of mono-deuterated acetylene (acetylene-d1, C2HD) in Titan''s atmosphere from the presence of two of its emission bands at 678 and 519 cm−1 as observed in CIRS spectral averages of nadir and limb observations taken between July 2004 and mid-2007. By using new laboratory spectra for this molecule, we were able to derive its abundance at different locations over Titan''s disk. We find the C2HD value () to be roughly constant with latitude from the South to about 45° N and then to increase slightly in the North, as is the case for C2H2. Fitting the 678 cm−1 band simultaneously with the nearby C2H2 729 cm−1 band, allows us to infer a D/H ratio in acetylene on Titan with an average of the modal values of from the nadir observations, the uncertainties being mainly due to the vertical profile used for the fit of the acetylene band. Although still subject to significant uncertainty, this D/H ratio appears to be significantly larger than the one derived in methane from the CH3D band (upper limit of ; Bézard, B., Nixon, C.A., Kleiner, I., Jennings, D.E., 2007. Icarus, 191, 397–400; Coustenis, A., Achterberg, R., Conrath, B., Jennings, D., Marten, A., Gautier, D., Bjoraker, G., Nixon, C., Romani, P., Carlson, R., Flasar, M., Samuelson, R.E., Teanby, N., Irwin, P., Bézard, B., Orton, G., Kunde, V., Abbas, M., Courtin, R., Fouchet, Th., Hubert, A., Lellouch, E., Mondellini, J., Taylor, F.W., Vinatier, S., 2007. Icarus 189, 35–62). From the analysis of limb data we infer D/H values of (at 54° S), (at 15° S), (at 54° N) and (at 80° N), which average to a mean value of . [Copyright &y& Elsevier]

Abstract: The Composite Infrared Radiometer–Spectrometer (CIRS) instrument, on the NASA Cassini Saturn orbiter, has been acquiring thermal emission spectra from the atmosphere of Titan since orbit insertion in 2004. Observation sequences for measuring stratospheric temperatures have been obtained using both a nadir mapping mode and a limb viewing mode. The limb observations give better vertical resolution, and give information from higher altitudes, while the nadir observations provide more complete longitude coverage. Because the scale height of Titan''s atmosphere is large enough so that emission from a grazing ray is influenced by horizontal temperature variations in the atmosphere, we have developed a two-dimensional temperature retrieval algorithm for reducing the limb spectra, which solves simultaneously for meridional and vertical temperature variations. The analyzed nadir mapping data have sampled nearly all longitudes at latitudes from about 90° S to 60° N, providing temperatures between pressure levels of about 5 to 0.2 mbar. The limb data covers latitudes between about 75° S and 85° N, and yields temperatures between about 1 and 0.005 mbar, at a small number of longitudes. The retrieved temperatures are consistent with early results from nadir observations [Flasar, F.M., and 44 colleagues, 2005. Science 308, 975–978] between 0.5 and 5 mbar where both results are valid, with the warmest temperatures at the equator, and much stronger meridional temperature gradients in the northern (winter) hemisphere than in the southern. At higher altitudes not probed by nadir viewing, the limb data reveal that the stratopause is nearly 20 K warmer in the northern polar regions than at the equator and southern hemisphere, and that the altitude of the stratopause shifts from ≈0.1 mbar (300 km) near the equator to 0.01 mbar (400 km) poleward of about 40° N. When the gradient wind equation is used to construct a zonal mean wind, the reversal in sign of the temperature leads to capping of the winter westerly flow. The core of the resulting jet is about 190 m s−1 in magnitude, spans between 30° N and 60° N, and peaks near 0.1 mbar. Estimates of the radiative heating associated with the radiative disequilibrium lead to a meridional overturning timescale of about three Earth years. [Copyright &y& Elsevier]

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−1 (7.18 μm). 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 , whereas in regions with thick clouds the peak cloud absorption coefficient occurs in the vicinity of 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. [Copyright &y& Elsevier]