Seasonal evolution of C2N2, C3H4, and C4H2 abundances in Titan’s lower stratosphere

Abstract

Aims. We study the seasonal evolution of Titan’s lower stratosphere (around 15 mbar) in order to better understand the atmospheric dynamics and chemistry in this part of the atmosphere. Methods. We analysed Cassini/CIRS far-IR observations from 2006 to 2016 in order to measure the seasonal variations of three photochemical by-products: C4H2, C3H4, and C2N2. Results. We show that the abundances of these three gases have evolved significantly at northern and southern high latitudes since 2006. We measure a sudden and steep increase of the volume mixing ratios of C4H2, C3H4, and C2N2 at the south pole from 2012 to 2013, whereas the abundances of these gases remained approximately constant at the north pole over the same period. At northern mid-latitudes, C2N2 and C4H2 abundances decrease after 2012 while C3H4 abundances stay constant. The comparison of these volume mixing ratio variations with the predictions of photochemical and dynamical models provides constraints on the seasonal evolution of atmospheric circulation and chemical processes at play.