Mountain torque and its influence on the atmospheric angular momentum on Titan

Tokano, Tetsuya

doi:10.1016/j.icarus.2012.06.027

Cited by 6 publications

(4 citation statements)

References 54 publications

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“…However, the development of the Köln model continued up to now, with studies mostly dedicated to Titan's troposphere (e.g. among the most recent works, Tokano et al 2011;Tokano 2012Tokano , 2019.…”

Section: A Short History Of Titan's General Circulation Modelsmentioning

confidence: 99%

Superrotation in Planetary Atmospheres

et al. 2020

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Superrotation is a dynamical regime where the atmosphere circulates around the planet in the direction of planetary rotation with excess angular momentum in the equatorial region. Superrotation is known to exist in the atmospheres of Venus, Titan, Jupiter, and Saturn in the solar system. Some of the exoplanets also exhibit superrotation. Our understanding of superrotation in a framework of circulation regimes of the atmospheres of terrestrial planets is in progress thanks to the development of numerical models; a global instability involving planetary-scale waves seems to play a key role, and the dynamical state depends on the Rossby number, a measure of the relative importance of the inertial and Coriolis forces, and the thermal inertia of the atmosphere. Recent general circulation models of Venus's and Titan's atmospheres demonstrated the importance of horizontal waves in the angular momentum transport in these atmospheres and also an additional contribution of thermal tides in Venus's atmosphere. The atmospheres of Jupiter and Saturn also exhibit strong superrotation. Recent gravity data suggests that these superrotational flows extend deep into the planet, yet currently no single mechanism has been identified as driving this superrotation. Moreover, atmospheric circulation models of tidally locked, strongly Understanding the Diversity of Planetary Atmospheres Edited by François Forget,

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Section: A Short History Of Titan's General Circulation Modelsmentioning

confidence: 99%

Superrotation in Planetary Atmospheres

et al. 2020

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“…Other effects may influence the atmospheric torque. Mitchell (2009) suggested the methane cycle could reduce the amplitude of the torque and produce a small drift while Tokano (2012) suggested the presence of mountains could increase the AAM a little without changing the torque very much. These effects remain poorly constrained but should only have a small impact.…”

Section: F1mentioning

confidence: 99%

Librational response of a deformed 3-layer Titan perturbed by non-Keplerian orbit and atmospheric couplings

Richard

Rambaux

Charnay

2014

Planetary and Space Science

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The analyses of Titan's gravity field obtained by Cassini space mission suggest the presence of an internal ocean beneath its icy surface. The characterization of the geophysical parameters of the icy shell and the ocean is important to constrain the evolution models of Titan. The knowledge of the librations, that are periodic oscillations around a uniform rotational motion, can bring piece of information on the interior parameters.The objective of this paper is to study the librational response in longitude from an analytical approach for Titan composed of a deep atmosphere, an elastic icy shell, an internal ocean, and an elastic rocky core perturbed by the gravitational interactions with Saturn. We start from the librational equations developed for a rigid satellite in synchronous spin-orbit resonance. We introduce explicitly the atmospheric torque acting on the surface computed from the Titan IPSL GCM (Institut Pierre Simon Laplace General Circulation Model) and the periodic deformations of elastic solid layers due to the tides. We investigate the librational response for various interior models in order to compare and to identify the influence of the geophysical parameters and the impact of the elasticity.The main librations arise at two well-separated forcing frequency ranges: low forcing frequencies dominated by the Saturnian annual and semi-annual frequencies, and a high forcing frequency regime dominated by Titan's or- bital frequency around Saturn. At low forcing frequency, the librational response is dominated by the Saturnian gravitational torque and the atmospheric torque has a small effect. In addition, the libration amplitude in that case is almost equal to the magnitude of the perturbation. The modulation of the gravitational torque amplitude at the orbital frequency with periodic deformation induces long-period terms in the librational response which contain information on the internal structure. At high forcing frequency the libration depends on the inertia of the layers and the elasticity can strongly reduce its amplitude at orbital frequency. For example, the amplitude of diurnal libration for oceanic models goes from about 320 − 390 meters if the icy shell is purely rigid to 60 − 85 meters when the elasticity is included, i.e. a reduction of about 80%. For models without ocean, diurnal libration goes from 52 meters in a rigid case to 50 meters for an elastic case, a very low reduction due to the weak deformation of an entirely solid satellite compared to the deformation of a thin icy shell. Oceanic models with elastic solid layers have the same order of libration amplitude than the oceanless models, which makes more challenging to differentiate them by the interpretation of librational motion.

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“…Due to the lack of knowledge about Titan's topography, this GCM has not yet been run with topography. The impact of a first‐approximation topography on the angular momentum budget has been recently studied by Tokano [2012] in the case of the Köln Titan GCM [ Tokano et al , 1999]. In these simulations, the dycore contribution was estimated and also shown to be non‐negligible both without and with topography.…”

Section: Analysis Of Angular Momentum Budgetsmentioning

confidence: 99%

Angular momentum budget in General Circulation Models of superrotating atmospheres: A critical diagnostic

et al. 2012

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1] To help understand the large disparity in the results of circulation modeling for the atmospheres of Titan and Venus, where the whole atmosphere rotates faster than the surface (superrotation), the atmospheric angular momentum budget is detailed for two General Circulation Models (GCMs). The LMD GCM is tested for both Venus (with simplified and with more realistic physical forcings) and Titan (realistic physical forcings).The Community Atmosphere Model is tested for both Earth and Venus with simplified physical forcings. These analyses demonstrate that errors related to atmospheric angular momentum conservation are significant, especially for Venus when the physical forcings are simplified. Unphysical residuals that have to be balanced by surface friction and mountain torques therefore affect the overall circulation. The presence of topography increases exchanges of angular momentum between surface and atmosphere, reducing the impact of these numerical errors. The behavior of GCM dynamical cores with regard to angular momentum conservation under Venus conditions provides an explanation of why recent GCMs predict dissimilar results despite identical thermal forcing. The present study illustrates the need for careful and detailed analysis of the angular momentum budget for any GCM used to simulate superrotating atmospheres.

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Mountain torque and its influence on the atmospheric angular momentum on Titan

Cited by 6 publications

References 54 publications

Superrotation in Planetary Atmospheres

Superrotation in Planetary Atmospheres

Librational response of a deformed 3-layer Titan perturbed by non-Keplerian orbit and atmospheric couplings

Angular momentum budget in General Circulation Models of superrotating atmospheres: A critical diagnostic

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