Seasonal variation of Titans atmospheric structuresimulated by a general circulation model

Tokano, Tetsuya; Neubauer, F. M.; Laube, M.; McKay, Christopher P.

doi:10.1016/s0032-0633(99)00011-2

Cited by 95 publications

(93 citation statements)

References 37 publications

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“…This difference is remarkable, but not altogether surprising. Titan's substantial orbital eccentricity modulates the insolation: Tokano et al (1999) have recently determined that this eccentricity effect causes the peak stratospheric summer temperature over the south pole to be 10 K warmer than the peak summer temperature in the north. This temperature difference may affect condensation processes on the haze as well as the circulation that blows the haze around.…”

Section: Discussion and Supporting Datamentioning

confidence: 99%

“…We find that seasonal change on Titan appears to occur faster than was expected. We introduce a simple physical model for these changes, invoking the latitudinal transport of haze particles as suggested by Hutzell et al (1996) and more recently elaborately modeled by Tokano et al (1999), and then attempt to quantify the number density, optical properties, and altitude of the haze responsible using detailed radiative transfer models.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal Change on Titan Observed with the Hubble Space Telescope WFPC-2

Lorenz

Lemmon

Smith

et al. 1999

Icarus

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Recent observations with the Wide-Field Planetary Camera (WFPC-2) on the Hubble Space Telescope (HST) show an unexpectedly rapid change in the atmospheric albedo contrast between the north and south hemispheres. In 1994 at blue wavelengths, the north was around 15% brighter than the south, and was expected to fall to about 12% in 1997, but has dropped to only 6% brighter. At some other wavelengths, the contrast has reversed, which was not expected until 2002. The interhemispheric contrast has a time dependence that varies with wavelength; contrast changes in blue lag behind changes in violet and yellow/red. The rapid change and the phase variation with wavelength are consistent with ground-based photometry. A physical model of the transport of high-altitude dark haze by meridional winds is a better description of Titan's behavior than the simple sinusoidal models used to date. Investigation with a radiative transfer model indicates that haze number density changes above 160-km altitude are compatible with the observed hemispheric albedo difference, and require particles >0.1 µm in radius.

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Section: Discussion and Supporting Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Seasonal Change on Titan Observed with the Hubble Space Telescope WFPC-2

Lorenz

Lemmon

Smith

et al. 1999

Icarus

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“…Hydrostatic Venus GCMs underestimate the magnitude of the superrotation if the models are run with realistic diabatic forcing, but the superrotation becomes more realistic if an excessive diabatic forcing is assumed below the cloud level [Hollingsworth et al, 2007;Yamamoto and Takahashi, 2009;Lebonnois et al, 2010], although there is also significant model dependency. The magnitude of the stratospheric zonal wind predicted by Titan GCMs is strongly model dependent and highly sensitive to model parameters, ranging from weak subrotation to strong superrotation [Hourdin et al, 1995;Tokano et al, 1999;Friedson et al, 2009;Newman et al, 2011;Lebonnois et al, 2012a].…”

Section: Introductionmentioning

confidence: 99%

Wind‐induced equatorial bulge in Venus and Titan general circulation models: Implication for the simulation of superrotation

Tokano

2013

Geophysical Research Letters

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[1] The centrifugal force associated with the superrotation in Venus' and Titan's middle atmosphere reduces the effective gravity and thereby modifies the shape of the geopotential surface, which manifests itself as an equatorial bulge. General circulation models (GCMs) based on the hydrostatic primitive equations cannot correctly represent this dynamics since the vertical component of the centrifugal force does not appear in the hydrostatic equation. Consequently, they are likely to underestimate the poleward pressure gradient force and superrotation in gradient wind balance. This effect can be accounted for in nonhydrostatic GCMs or in quasi-hydrostatic GCMs, in which the hydrostatic equation is supplemented by the vertical component of the centrifugal and Coriolis force and which do not make the shallow-atmosphere approximation. A quasi-hydrostatic GCM is shown to predict faster superrotation than a hydrostatic GCM run under otherwise identical conditions. Citation: Tokano, T. (2013), Wind-induced equatorial bulge in Venus and Titan general circulation models: Implication for the simulation of superrotation, Geophys. Res. Lett., 40,[4538][4539][4540][4541][4542][4543]

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“…Simulations by Tokano et al (1999) and Richardson et al (2007) achieved equatorial winds of approximately 10-20 m s K1 . The reason for the dispersion in results is not obvious.…”

Section: General Circulation Model Studiesmentioning

confidence: 94%

The structure and dynamics of Titan's middle atmosphere

Flasar

Achterberg

2008

Phil. Trans. R. Soc. A.

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Titan's middle atmosphere is characterized by cyclostrophic winds and strong seasonal modulation. Cassini CIRS observations, obtained in northern winter, indicate that the stratosphere near 1 mbar is warmest at low latitudes, with the South Pole a few degrees colder and the North Pole approximately 20 K colder. Associated with the cold northern temperatures are strong circumpolar winds with speeds as high as 190 m s K1 . Within this vortex, the mixing ratios of several organic gases are enhanced relative to those at low latitudes. Comparison with Voyager thermal infrared measurements, obtained 25 years ago in northern spring, suggests that the enhancement currently observed will increase as the winter progresses. The stratopause height increases from 0.1 mbar near the equator to 0.01 mbar near the North Pole, where it is the warmest part of the atmosphere, greater than 200 K. This implies subsidence at the pole, which is consistent with the enhanced organics observed. Condensate features, several still not identified, are also apparent in the infrared spectra at high northern latitudes. In many ways, the winter vortex observed on Titan, with cyclostrophic winds, resembles the polar winter vortices on the Earth, where the mean winds are geostrophic.

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Seasonal variation of Titans atmospheric structuresimulated by a general circulation model

Cited by 95 publications

References 37 publications

Seasonal Change on Titan Observed with the Hubble Space Telescope WFPC-2

Seasonal Change on Titan Observed with the Hubble Space Telescope WFPC-2

Wind‐induced equatorial bulge in Venus and Titan general circulation models: Implication for the simulation of superrotation

The structure and dynamics of Titan's middle atmosphere

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