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Register a new userSeasonal evolution of $mathrm{C_2N_2}$, $mathrm{C_3H_4}$, and $mathrm{C_4H_2}$ abundances in Titans lower stratosphere
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Added by
M\\'elody Sylvestre
Publication date
2017
fields
Physics
and research's language is
English
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We study the seasonal evolution of Titans lower stratosphere (around 15~mbar) in order to better understand the atmospheric dynamics and chemistry in this part of the atmosphere. We analysed Cassini/CIRS far-IR observations from 2006 to 2016 in order to measure the seasonal variations of three photochemical by-products: $mathrm{C_4H_2}$, $mathrm{C_3H_4}$, and $mathrm{C_2N_2}$. 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 $mathrm{C_4H_2}$, $mathrm{C_3H_4}$, and $mathrm{C_2N_2}$ 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, $mathrm{C_2N_2}$ and $mathrm{C_4H_2}$ abundances decrease after 2012 while $mathrm{C_3H_4}$ 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.
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The Cassini mission offered us the opportunity to monitor the seasonal evolution of Titans atmosphere from 2004 to 2017, i.e. half a Titan year. The lower part of the stratosphere (pressures greater than 10 mbar) is a region of particular interest as there are few available temperature measurements, and because its thermal response to the seasonal and meridional insolation variations undergone by Titan remains poorly known. In this study, we measure temperatures in Titans lower stratosphere between 6 mbar and 25 mbar using Cassini/CIRS spectra covering the whole duration of the mission (from 2004 to 2017) and the whole latitude range. We can thus characterize the meridional distribution of temperatures in Titans lower stratosphere, and how it evolves from northern winter (2004) to summer solstice (2017). Our measurements show that Titans lower stratosphere undergoes significant seasonal changes, especially at the South pole, where temperature decreases by 19 K at 15 mbar in 4 years.
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