Contrasting Responses to Orbital Precession on Titan and Earth

Abstract:

Earth and Titan exhibit contrasting atmospheric responses to orbital precession. On Earth, most (water) precipitation falls in low latitudes, and more falls in the hemisphere with summer perihelion. On Titan, most (methane) precipitation falls in high latitudes, and more falls in the hemisphere with summer aphelion. We use a Titan general circulation model to elucidate the dynamical reasons for these different responses to orbital precession. They arise primarily because of the different rotation rates of Titan and Earth. The slower rotation rate of Titan leads to wider Hadley cells that transport moisture into polar regions. Variations in the length of summer near the poles, rather than in the intensity of summer insolation as in Earth's tropics, then dominate the precession response of the hydrologic cycle. We also investigate the generation, propagation and dissipation of the methane storms in the climates with different rotation rates.