Equatorial Waves And Superrotation In The Stratosphere Of A Titan General Circulation Model

By Keith Cowing
Status Report
July 13, 2023
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Equatorial Waves And Superrotation In The Stratosphere Of A Titan General Circulation Model
Zonal-mean zonal wind u and TEM streamfunction Ψ ∗ for northern hemisphere late summer and late autumn. Six contour levels are shown for Ψ ∗ at ±107 , ±108 and ±109 kg s−1 (negative contours dashed). Positive Ψ ∗ indicates clockwise overturning. — astro-ph.EP

We investigate the characteristics of equatorial waves associated with the maintenance of superrotation in the stratosphere of a Titan general circulation model.

A variety of equatorial waves are present in the model atmosphere, including equatorial Kelvin waves, equatorial Rossby waves, and mixed Rossby-gravity waves. In the upper stratosphere, acceleration of superrotation is strongest around solstice and is due to interaction between equatorial Kelvin waves and Rossby-type waves in winter-hemisphere mid-latitudes.

The existence of this ‘Rossby-Kelvin’-type wave appears to depend on strong meridional shear of the background zonal wind that occurs in the upper stratosphere at times away from the equinoxes. In the lower stratosphere, acceleration of superrotation occurs throughout the year and is partially induced by equatorial Rossby waves, which we speculate are generated by quasigeostrophic barotropic instability. Acceleration of superrotation is generally due to waves with phase speeds close to the zonal velocity of the mean flow.

Consequently, they have short vertical wavelengths which are close to the model’s vertical grid scale, and therefore are likely to be not properly represented. We suggest this may be a common issue amongst Titan GCMs which should be addressed by future model development.

Neil T. Lewis, Nicholas A. Lombardo, Peter L. Read, Juan M. Lora

Comments: Accepted for publication in The Planetary Science Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph); Fluid Dynamics (physics.flu-dyn)
Cite as: arXiv:2307.06745 [astro-ph.EP] (or arXiv:2307.06745v1 [astro-ph.EP] for this version)
Submission history
From: Neil Lewis
[v1] Thu, 13 Jul 2023 13:37:08 UTC (9,857 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻