Seasonal Changes in Titan’s Upper Haze Resulting from Saturn’s Eccentric Orbit

Organic aerosols are produced high in the atmosphere of Titan by complex photochemical pathways starting from the dissociation of CH4 by solar ultraviolet (UV) and N2 by energetic particles. An end product of this photochemistry is the organic haze enshrouding Titan. The solar flux at Titan varies by about 20% between periapsis and apoapsis, thus we expect the dissociation of CH4 and the total production of aerosols to have a similar seasonal dependence. The seasonal cycle in the haze production due to Saturn's orbital eccentricity is complicated by seasonal changes in dynamics and aerosol particle size due to Saturn's 27° obliquity. A 3D Titan general circulation model with fully coupled aerosol microphysics, the Titan Community Atmospheres Model, simulates the aerosol haze with and without aerosol production as a function of solar UV. Both simulations display an equatorial seasonal cycle in the haze above about 340 km; however, this cycle is amplified by a factor of 2 in the simulation with production as a function of solar UV. We compare the simulations with published estimates of haze extinction in the upper atmosphere. Current observations of the haze extinction at 400 km cannot distinguish between the two simulations, highlighting the difficulties that complicated dynamics in the upper atmosphere pose for trend detection.