Publications of the MPIfR
Optical & Infrared
Interferometry Group
Kostiuk, T.; Livengood, T. A.;
Sonnabend, G.; Fast, K. E.; Hewagama, T.; Murakawa, K.; Tokunaga, A.
T.; Annen, J.; Buhl, D.; Schmülling, F.; Luz, D.; Witasse, O.
Stratospheric global winds on Titan at the time
of Huygens descent
Journal of Geophysical Research, Volume 111, Issue
E7
Abstract
Measurements of stratospheric zonal winds on Titan were made in
preparation for and during the time of the descent of the Huygens Probe
into Titan's atmosphere on 14 January 2005. Fully resolved emission
lines from ethane near 11.7 μm were measured on the east, center, and
west positions on Titan using the NASA/GSFC Heterodyne Instrument for
Planetary Wind And Composition, HIPWAC, mounted on the National
Astronomical Observatory of Japan 8.2 m Subaru Telescope on Mauna Kea,
Hawaii. Analysis of the Doppler shifts of the emission line shapes
yielded mean prograde gas velocity ~60 +/- 65 m/s at altitudes below
~120 km (~5 mbar). This result is consistent with retrievals from the
Huygens Doppler Wind Experiment and from other observations near this
altitude range. Current spectral line shapes, however, differed
significantly from those obtained in similar measurements on Subaru in
2004 and on the NASA IRTF in 1993-1996, which retrieved prograde zonal
winds 190 +/- 90 m/s at 230 km (~0.4 mbar). The cores of the emission
lines, which probe the high-altitude region, could not be fitted as
before to retrieve wind directly using the accepted atmospheric model
for Titan. They imply an approximately tenfold increase in ethane mole
fraction (1.2 × 10-4) with strong wind shear above the stratopause,
providing a potential probe of the lower mesosphere and possible
evidence of temporal and spatial variability. Results contribute to
coordinated measurements of winds by various techniques providing
information on the altitude distribution of wind velocity in Titan's
atmosphere from near the surface to the lower mesosphere.
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