The dynamics of Titan's troposphere

Abstract

While the Voyager mission could essentially not reveal the dynamics of Titan's troposphere, useful information was obtained by the Cassini spacecraft and, particularly, by the Huygens probe that landed on Titan's surface; this information can be interpreted by means of numerical models of atmospheric circulation. The meridional circulation is likely to consist of a large Hadley circulation asymmetric about the equator, but is susceptible to disruption by turbulence in clouds. The zonal wind in the troposphere is comparable to or even weaker than that in the terrestrial troposphere and contains zones of easterlies, much in contrast to the super-rotating stratosphere. Unique to Titan is the transition from a geostrophic to cyclostrophic wind balance in the upper troposphere. While Earth-like storm systems associated with baroclinic instability are absent, Saturn's gravitational tide introduces a planetary wave of wavenumber 2 and a periodical variation in the wind direction in the troposphere. Unlike on Earth, the wind over the equatorial surface is westerly. The seasonal reversal in the Hadley circulation sense and zonal wind direction is predicted to have a substantial influence on the formation of dunes as well as variation of Titan's rotation rate and length of day.

Surface, Subsurface and Atmosphere Exchanges on the Satellites of the Outer Solar System

“…The eastward orientation of the longitudinal dunes ) apparently contradicts wind directions predicted by GCMs. As a matter of fact, not a single GCM predicts eastward winds right at the equatorial surface, and it is currently unknown what mechanism controls the zonal wind at the surface (Tokano 2009). …”

Energy Options for Future Humans on Titan

“…Wind speeds are higher on Titan (~2 m/s) at ~3 km altitude [21] and even higher (~20 m/s) at 40 km altitude [22]; tethered balloon or blimp-borne [23,24] power-generating windmills could be feasible to access these higher wind speeds for greater energy generation, on the order of hundreds of MW.…”

Planetary Atmospheres

“…With slow rotation, if the Ro ≳ 10, a planet behaves as an 'all tropics' world because Hadley cells extend to high latitudes (Showman et al, 2013). Possibly, the dunes form during periods when equatorial zonal winds reverse and strengthen (Tokano, 2009(Tokano, , 2010 (see Chapter 10.12). On Venus, $20 W m À2 of sunlight reaches the surface (Titov et al, 2007), so the Hadley circulation must be weak.…”