Interferometric measurements of zonal winds on Titan

Abstract

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.

First disk-resolved millimeter observations of Io's surface and SO2atmosphere

“…When this is combined with the noise level and the ∼50 m/s uncertainty associated with the deconvolution process, the disk center shift may in fact be consistent with zero. We note that similar Doppler shift measurements on Titan obtained with PdBI (Moreno et al 2005) also indicate unexplained disk center shifts at the level of ±40 m/s. In this situation, relative frequency measurements are much more precise, and the best determined parameter is the limb-to-limb difference in Doppler shift, found to be 330 ± 100 m/s.…”

Titan's stratospheric zonal wind, temperature, and ethane abundance a year prior to Huygens insertion

“…The altitude where maximum wind is retrieved is !220 km, at the altitude limit probed by CIRS at low latitudes from temperature maps (wind speed$100 -160 m/s), and covers the near-equatorial region not measured by CIRS [Flasar et al, 2005]. A comprehensive altitude structure of circulating winds can be established from Cassini, Huygens, and ground-based measurements with HIPWAC as well as techniques such as UVES probing $100 -200 km [Luz et al, 2003] and mm-wave studies probing !300 km [Moreno et al, 2005].…”

First detection of hydrogen isocyanide (HNC) in Titan’s atmosphere

“…Despite these impressive results, from which a completely new view of Titan's ion-neutral chemistry emerged, INMS cannot distinguish between species of identical mass, in particular between isomers. Heterodyne spectroscopy of strong rotational lines provides high sensitivity and frequency discrimination for the detection of minor species with permanent dipole moment -such as HCN, HC 3 N and CH 3 CN (Marten et al 2002;Gurwell 2004), and CO (Gurwell & Muhleman 1995;Hidayat et al 1998;Rengel et al 2011) -and allows for full resolution of line profiles, as well as unique absolute wind measurements in Titan's stratosphere and mesosphere from mapping of the Doppler shift in spatially-resolved data (Moreno et al 2005).…”