Titan's asymmetric lake distribution mediated by methane transport due to atmospheric eddies

The hemispheric asymmetry of Titan's surface methane has been proposed to be a consequence of orbital forcing affecting Titan's hydrologic cycle, but the mechanism behind asymmetrical transport of moisture remains to be examined. Using general circulation model simulations of Titan's atmosphere, we show that atmospheric moisture transport by three-dimensional tropospheric eddies is critical in generating Titan's surface liquid asymmetry. Comparison of axisymmetric and three-dimensional simulations demonstrates that a significant asymmetry only develops in the latter case. Analysis of the components of the three-dimensional moisture transport reveals that nonaxisymmetric eddies transport methane away from the poles and into the midlatitudes, where they transfer moisture into the cross-equatorial transport by the mean meridional circulation, producing an atmospheric bucket brigade. Because these high-latitude, baroclinic eddies are more intense in the south than in the north, the net transport is preferentially northward, with the northern hemisphere gaining surface liquid at the expense of the southern hemisphere.