Actinic fluxes in Titan's atmosphere, from one to three dimensions: Application to high-latitude composition

We present a study on diurnally and annually averaged values of the actinic fluxes used in one-dimensional (1-D) photochemical models, as well as a 3- D radiative transfer model, based on Monte Carlo calculations with applicat ion to the atmosphere of Titan. This study shows that the commonly used val ue <theta >=30 degrees for the mean incident angle at the equator in photoc hemical models of Titan is not the best choice, though changing the value h as no dramatic effects on photochemistry. The results of the 3-D code give direct access to the photolysis rates at any point in the atmosphere, The n ecessity of 3-D values in a deep atmosphere such as Titan's is demonstrated particularly for high-latitude winter conditions, These 3-D photolysis rat es are used to model the latitudinal variations of the chemical composition of Titan's atmosphere in a 1-D photochemical model adapted to different la titudes. This study shows that these kinds of simple photochemical models c annot reproduce the observed latitudinal behavior and that we need to devel op real 2-D photochemical models of Titan's atmosphere.