Null Variance Altitudes for the photolysis rate constants of species with barometric distribution: Illustration on Titan upper atmosphere modeling |
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Authors: | Zhe Peng Fabien Cailliez Michel Dobrijevic Pascal Pernot |
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Institution: | 1. Laboratoire de Chimie Physique, Bât. 349, Univ. Paris-Sud, F-91405 Orsay Cedex, France;2. CNRS, UMR 8000, F-91405 Orsay Cedex, France;3. Université de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 2 rue de l’Observatoire, BP 89, F-33271 Floirac Cedex, France;4. CNRS, UMR 5408, Laboratoire d’Astrophysique de Bordeaux, 2 rue de l’Observatoire, BP 89, F-33271 Floirac Cedex, France |
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Abstract: | The precision of the rates of the photolysis processes initiating the complex chemistry of Titan’s upper atmosphere conditions strongly the predictivity of photochemical models. Recent studies in sensitivity analysis of such models point out photolysis rate constants as key parameters. However, they have been treated approximately so far. We deal here directly with uncertainty in the absorption cross-sections to derive the uncertain altitude-dependent photolysis rate constants. We observe that the uncertainty on the photolysis rate constants of the major species, N2 and CH4, varies strongly with altitude and rather surprisingly vanishes at specific altitudes. We propose a simple model to interpret these features and we demonstrate that they are transferable to any major absorber distributed barometrically in an atmosphere. |
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