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

Kostiuk, T.; Livengood, T. A.; Hewagama, T.; Sonnabend, G.; Fast, K. E.; Murakawa, K.; Tokunaga, A. T.; Annen, J.; Bühl, D.; Schmülling, F.

doi:10.1029/2005gl023897

Cited by 39 publications

(34 citation statements)

References 22 publications

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“…This correlation and phase change would occur if the temperatures were zonally symmetric about an axis of rotation that was offset from Titan's pole. To check this, a function minimization algorithm (Nelder and Mead, 1965) was used to find the rotation axis offset that minimizes the global variance of the 1 mbar temperatures from their zonal mean. The amplitude and phase of zonal wavenumber 1 in the resulting tilted reference frame, with a rotation pole offset from the IAU definition of Titan's pole (Seidelmann et al, 2007) by 4.1 • , is shown in Figs.…”

Section: Discussionmentioning

confidence: 99%

Observation of a tilt of Titan's middle-atmospheric superrotation

Achterberg

Conrath

Gierasch

et al. 2008

Icarus

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Section: Discussionmentioning

confidence: 99%

Observation of a tilt of Titan's middle-atmospheric superrotation

Achterberg

Conrath

Gierasch

et al. 2008

Icarus

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“…From this latitudinal density gradient we inferred zonal wind speeds in Titan's thermosphere of the order of 245±50 ms −1 , which are close to the sound speed. Wind speeds of the order of 60–200 ms −1 have been observed in Titan's stratosphere and lower mesosphere from ground‐based observations [ Hubbard et al , 1993; Kostiuk et al , 2001, 2005; Luz et al , 2005; Moreno et al , 2005; Sicardy et al , 2006] as well as recent infrared observations by Cassini's Composite Infrared Spectrometer (CIRS) [ Flasar et al , 2005].…”

Section: Discussionmentioning

confidence: 99%

Waves and horizontal structures in Titan's thermosphere

et al. 2006

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[1] The Ion Neutral Mass Spectrometer (INMS) on board the Cassini spacecraft carried out in situ measurements of neutral gas composition above 1025 km altitude in Titan's atmosphere during its flybys in October 2004 (TA) and April 2005 (T5). Strong perturbations are present in the N 2 and CH 4 densities which we interpret as vertically propagating waves. Typical vertical wavelengths range from 170 to 360 km with density and pressure amplitudes reaching 4-12% of the background values and temperature amplitudes of 5-10 K. Amplitudes over our sampled height range, 1025 (T5) or 1176 (TA) to 1600 km, remain roughly constant, implying that the exponential increase in wave amplitudes with height due to the decrease of density is offset by damping. This finding allows us to constrain the wave periods to values in the order of hours. Estimates of wave-induced acceleration of the background thermosphere suggest that the waves we observe could deposit considerable momentum in Titan's thermosphere, thereby coupling the dynamics of the upper atmosphere with that of the middle atmosphere. In addition, we infer latitudinal structures in Titan's thermosphere with a factor of 3-4 increase of mass densities from pole to equator in the northern hemisphere. A preliminary evaluation of local time variations suggests densities and thermospheric temperatures to be largest near dusk, contradicting expectations for a thermosphere driven energetically and dynamically primarily by solar EUV. From the latitudinal density gradients we derived zonal wind speeds of around 245 ± 50 ms À1 , implying that Titan's thermosphere, like its stratosphere, could be superrotating. Our analyses were based on the TA and TS flybys only, and future Cassini Titan flybys could either support or invalidate our findings.

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“…In order to measure the global circulation at cloud top altitude, we need to address wind amplitude variations (or wind latitudinal gradients) on the order of 5-10 m/s projected on the line-of-sight (Widemann et al, 2007). Such an accuracy cannot be achieved by single line fitting, even at high spectral resolution (with the exception of very high resolution heterodyne techniques, which require dedicated instrumentation; Kostiuk et al, 2001Kostiuk et al, , 2005Sonnabend et al, 2006Sonnabend et al, , 2008Sonnabend et al, , 2010. Therefore, it becomes necessary to optimally measure relative Doppler shifts between two sets of absorption lines (Connes, 1985), while simultaneously monitoring the change in spectral calibration with time .…”

Section: Introductionmentioning

confidence: 99%