Venus upper atmosphere winds from ground-based heterodyne spectroscopy of CO ₂ at 10µm wavelength

Abstract

We report observations of Venus atmospheric wind near 110 km altitude by means of high-resolution mid-infrared spectroscopy. Data were acquired May 28-June 4, 2007 at the McMath-Pierce Solar Telescope (Kitt Peak, Arizona, USA), during a coordinated ground-based observing campaign in support of Venus Express. The Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) was used to measure the Doppler shift of fully resolved non-LTE emission lines of CO ₂ at 959.3917cm^-1(10.423μm) to determine wind velocity. Spatial resolution was ∼1.7arcsec on Venus' apparent diameter of 20-22 arcsec. Zonal wind velocities were retrieved at six different latitudes close to the west limb. Retrieved zonal velocities - parallel to Venus' retrograde solid body rotation - range 3±7m/s(1σ) at the equator to a maximum of 32±4m/s(1σ) at southern mid-latitude (45^∘S), decreasing at higher latitudes and thus suggesting a retrograde double jet structure for the zonal component. The subsolar-to-antisolar circulation component was measured at one position, 45^∘ towards the sunlit limb from the central meridian, on the equator. The retrieved subsolar-to-antisolar component at this position implies a cross-terminator velocity of 52±18m/s(1σ). Retrieved velocities are lower than previous results, suggesting spatial and/or temporal variability of dynamics in the mesosphere/thermosphere of Venus.