Which Way Does the Wind Blow? Titan's Zonal Circulation

Theodor Kostiuk, Kelly Fast, Tim Livengood, Fred Espenak, David Buhl (NASA/Goddard Space Flight Center), Jeffrey Goldstein, Tilak Hewagama, Kyung Ho Ro (Challenger Center)

Knowledge of the direction and magnitude of Titan's circulation is important for the Cassini Huygens Probe mission and for constraining dynamical models of slowly rotating bodies. Ethane emission lines from Titan's stratosphere were measured with a spectral resolving power of tex2html_wrap_inline11 using the Goddard Infrared Heterodyne Spectrometer at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii in August 1993, October 1995 and September 1996. A comparison of the retrieved line center frequencies of the resolved lineshapes from the east and west hemispheres of Titan provides a measure of the direction and a mean magnitude of the speed of the circulation in the 7-0.1 mbar pressure altitude regions (120-350 km). The relative Doppler shift of the lines from the two hemispheres yields a prograde wind direction and an average limb-to-limb magnitude of tex2html_wrap_inline13  m/sec ( tex2html_wrap_inline15 m/sec horizontal). The instrumental stability permits absolute measurements to tex2html_wrap_inline17  m/s, while the signal-to-noise on the data limits the limb-to-limb uncertainty to tex2html_wrap_inline19  m/sec. Recent improved analyses and interpretation will be discussed.