Venus upper atmosphere winds from ground-based heterodyne spectroscopy of CO2 at 10μm wavelength

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We present wind measurements in the Venusian upper mesosphere / lower thermosphere (at an altitude of 100-120km) by means of infrared heterodyne spectroscopy of CO2 P(2) features at 959.3917 cm-1. Provided high spectral resolution winds can be retrieved from Doppler-shifts of CO2 non-thermal emission lines.The mesosphere is the not very well understood transitions zone form the superrotating zonal circulation (RSZ) dominated troposphere and the subsolar to anti-solar flow (SS-AS flow) dominated thermosphere [1,2] hence the addressed altitude region is of special interest. Observations are carried out systematically on the day-side of the planet using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS). Measurements were gathered during two observing runs: a) May 25 to June 6 2007 at the McMath-Pierce solar telescope on KittPeak/Arizona; b) November 21-28 2007 at the McMath-Pierce solar telescope on KittPeak/Arizona; Both times Venus illumination was about 50%. Run a) took place shortly before Venus superior conjunction and b) shortly after Venus superior conjunction. Several positions on the planet with a diameter of approx. 20" were measured during each observing run. The telescope with a 1.5m main mirror provided a beamsize of 1.7". Zonal wind velocities as well as values for the SS-AS flow were retrieved and will be presented. The data analyzed so far show weak zonal wind velocities (from 3±7m/s to 32 ±4m/s ) with minimum values at the equator and maximum values at mid latitudes. Also the retrieved speed of the SS-AS flow was significantly lower than found by previous observations [3,4,5]. Together with results from space missions [6,7] and complementary ground based observing methods [8,3,4,5] probing wind velocities at different altitudes in the atmosphere of Venus, these measurements can provide global information about dynamical properties and increase the understanding about our neighbor planet. [1] Gierasch, P.J. et al. (1997) University of Arizona Press, 459. [2] Bougher, S.W. et al. (1986) Icarus, 68, 284-312. [3] Lellouch, E. et al. (1994) Icarus, 110, 315-339. [4] Shah, K et al. (1991) Icarus, 93, 96-121. [5] Goldstein, J. et al. (1991) Icarus, 94, 45-63. [6] Drossart, P. et al. (2007) Nature, 450(7170), 641- 645. [7] Markiewicz, W.J. et al. (2007) Nature, 450(7170), 633-636. [8] Widemann, T. et al. (2007) Planetary and Space Science, 55, 1741-1756.

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