The coupling of winds, aerosols and chemistry in Titan's atmosphere

Abstract

The atmosphere of Titan is a complex system, where thermal structure, radiative transfer, dynamics, microphysics and photochemistry are strongly coupled together. The global climate model developed over the past 15 years at the Pierre-Simon Laplace Institute has been exploring these different couplings, and has demonstrated how they can help to interpret the observed atmospheric structure of Titan's lower atmosphere (mainly in the stratosphere and troposphere). This review discusses these interactions, and our current understanding of their role in the context of this model, but also of other available works. The recent Cassini results, and the importance of the production mechanisms for Titan's haze, have put forward the need to explore the mesosphere and the couplings between upper and lower atmosphere, as well as the current limits of available models.

Possible climates on terrestrial exoplanets

“…On Mars, assuming the right amount of dust in the atmosphere it has been relatively easy to simulate the thermal structure of the atmosphere and the behaviour of atmospheric waves, such as thermal tides and baroclinic waves [70][71][72][73][74][75][76], to reproduce the main seasonal characteristics of the water cycle [77,78] or to predict the detailed behaviour of ozone [79,80]. On Titan, GCMs have anticipated the super-rotating wind fields with amplitude and characteristics comparable to observations [81,82] and allowed to simulate and interpret the detached haze layers [83,84], the abundance and vertical profiles of most chemical compounds in the stratosphere and their enrichment in the winter polar region [85], the distribution of clouds [86] or the detailed thermal structure observed by Huygens in the lowest 5 km [87]. On Venus, the development of 'full' GCMs (i.e.…”

Atmospheric/Exospheric Characteristics of Icy Satellites

“…The hemispheric asymmetry and its seasonal reversal are largely explained by global transport of aerosols across the equator (Lorenz et al 1999). The spatial distribution of stratospheric haze, which primarily changes with season, is predicted to have a large impact on the atmospheric circulation down to the surface and the surface temperature by affecting the radiation balance (Lebonnois et al 2009). …”

Composition and chemistry of Titan's stratosphere

“…This can be explained by subsidence in the winter polar vortex, bringing air enriched in photochemical compounds from the upper atmosphere where they are formed down to the stratosphere (Lebonnois et al 2009 and references therein). The stronger enrichment observed by Voyager at spring equinox implies that subsidence persists throughout winter, as predicted by global circulation models (GCMs).…”

“…These models incorporate chemical sinks and losses (photodissociation, 2-and 3-body reactions) and vertical transport parametrized by an altitude-varying eddy mixing coefficient. Two-dimensional models that couple a GCM and photochemistry have also been developed (see Lebonnois et al 2009) to study the seasonal and latitudinal variations of composition.…”