Seasonal Stratospheric Photochemistry on Uranus and Neptune.

A time-variable 1D photochemical model is used to study the distribution of stratospheric hydrocarbons as a function of altitude, latitude, and season on Uranus and Neptune. The results for Neptune indicate that in the absence of stratospheric circulation or other meridional transport processes, the hydrocarbon abundances exhibit strong seasonal and meridional variations in the upper stratosphere, but that these variations become increasingly damped with depth due to increasing dynamical and chemical time scales. At high altitudes, hydrocarbon mixing ratios are typically largest where the solar insolation is the greatest, leading to strong hemispheric dichotomies between the summer-to-fall hemisphere and winter-to-spring hemisphere.

Photochemistry on Pluto - I. Hydrocarbons and aerosols.

In light of the recent flyby measurements, we present a coupled ion-neutral-photochemistry model developed for simulating the atmosphere of Pluto. Our model results closely match the observed density profiles of CH, N and the C hydrocarbons in the altitude range where available measurements are most accurate (above ~ 100-200 km). We found a high eddy coefficient of 10 cm s from the surface to an altitude of 150 km, and 3 × 10 cm s above 150 km for Pluto's atmosphere.

Photochemistry on Pluto: part II HCN and nitrogen isotope fractionation.

We have converted our Titan one-dimensional photochemical model to simulate the photo- chemistry of Pluto's atmosphere and include condensation and aerosol trapping in the model. We find that condensation and aerosol trapping are important processes in producing the HCN altitude profile observed by the Atacama Large Millimeter Array (ALMA). The nitrogen iso- tope chemistry in Pluto's atmosphere does not appear to significantly fractionate the isotope ratio between N and HCN as occurs at Titan.