Abstract. We describe observations of Neptune carried out using the James Clerk Maxwell Telescope (Mauna Kea, Hawaii) during September 1998. High-quality data for the sub-mm-wavelength rotational transitions of HCN (J = 4−3) and CO (J = 3−2 and 4−3) were obtained, and we use the data to make improved determinations of the abundances of these trace species and the temperature profile of Neptune's atmosphere.

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Winds in Titan's lower and middle atmosphere have been determined by a variety of techniques, including direct measurements from the Huygens Probe 1 over 0-150 km, Doppler shifts of molecular spectral lines in the optical, thermal infrared and mm ranges 2-4 , probing altogether the ~100-450 km altitude range, and inferences from thermal field over 10 mbar -10 -3 mbar (i.e. ~100-500 km) 5-6 and from central flashes in stellar occultation curves 7-9 . These measurements predominantly indicated strong prograde winds, reaching maximum speeds of ~150-200 m/s in the upper stratosphere, with important latitudinal and seasonal variations. However, these observations provided incomplete atmospheric sounding; in particular, the wind regime in Titan's upper mesosphere and thermosphere (500-1200 km) has remained unconstrained so far. Here we report direct wind measurements based on Doppler shifts of six molecular species observed with ALMA. We show that unlike expectations, strong prograde winds extend up to the thermosphere, with the circulation progressively turning into an equatorial jet regime as altitude increases, reaching ~340 m/s at 1000 km. We suggest that these winds may represent the dynamical response of forcing by waves launched at upper stratospheric/mesospheric levels and/or magnetospheric-ionospheric interaction. We also demonstrate that the HNC distribution is restricted to Titan's thermosphere above ~870 km altitude.

Abstract.We report millimetre observations of Titan performed with the IRAM Plateau de Bure Interferometer at the rotational frequencies of HC 3 N(25-24) and CH 3 CN(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 (λ/∆λ = 5.5 × 10 6 ). 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 (±60) m/s and 60 (±20) m/s are determined at respective altitudes of 300 (±150) km (upper stratosphere) and 450 (±100) km (lower mesosphere). The latter is the first direct determination of mesospheric wind speed on Titan.

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