Interferometric measurements of zonal winds on Titan

We report millimetre observations of Titan performed with the IRAM Plateau de Bure Interferometer at the rotational frequencies of HC3N(25–24) and CH3CN(12–11). The most extended configuration of the array yielded disk-resolved emission spectra of Titan with an angular resolution of 0.6´´. Data were acquired in February–March 2003 and February 2004 near the greatest eastern and western elongations of Titan at high spectral resolution ( 106). Doppler lineshift measurements enable us to establish that the zonal wind flow is prograde in the upper atmosphere. Two different altitude regions are probed. Beam–integrated equatorial wind velocities of 160 () m/s and 60 () m/s are determined at respective altitudes of 300 () km (upper stratosphere) and 450 () km (lower mesosphere). The latter is the first direct determination of mesospheric wind speed on Titan.