Photochemical response to the variation of temperature in the 2011−2012 stratospheric vortex of Saturn

¹ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
e-mail: cavalie@mps.mpg.de
² Univ. Bordeaux, LAB, UMR 5804, 33270 Floirac, France
³ CNRS, LAB, UMR 5804, 33270 Floirac, France
⁴ Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
⁵ Institut des Sciences Moléculaires, UMR 5255, CNRS-Université de Bordeaux, 351 cours de la libération, 33405 Talence Cedex, France

Received: 2 December 2014
Accepted: 16 June 2015

Abstract

Context. A hot vortex formed in the stratosphere of Saturn following the 2010−2011 Northern Storm. Huge temperature increases have been measured in the vortex around the millibar level. Enhancements in hydrocarbon abundances have been observed at the millibar level in 2011−2012 inside this vortex.

Aims. We model the time-dependent photochemistry inside the vortex by accounting for the temperature variability over the period from January 2011 to March 2012 to assess whether photochemistry alone can explain the enhancements seen in the hydrocarbon abundances.

Methods. We used a 1D time-dependent photochemical model of Saturn and adapted it to the perturbed conditions of the vortex after validating it in quiescent conditions.

Results. Our model predicts non-variability for ethane (C₂H₆) and acetylene (C₂H₂) and an increase in ethylene (C₂H₄) by a factor of 3 in the mbar region. Heavier hydrocarbons show a stronger variability than the lighter ones. We are unable to reproduce the increase seen in C₂H₂ , and we significantly underestimate the increase seen in C₂H₄.

Conclusions. Pure photochemistry does not explain the variability seen in the abundance of most hydrocarbons. This means that dynamics (eddy diffusion and/or advection) must have played a significant role in shaping the vertical profiles of the main hydrocarbons.