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| Titel |
Atmospheric chemical and thermal structure evolution after one Titan year |
| VerfasserIn |
Athena Coustenis, Georgios Bampasidis, Richard Achterberg, Panayiotis Lavvas, Sandrine Vinatier, Conor Nixon, Donald Jennings, Nicolas Teanby, F. Michael Flasar, Ronald Carlson, Glenn Orton, Paul Romani, Ever Guandique |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077545
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| Zusammenfassung |
| Our radiative transfer code (ARTT) was applied to Cassini Composite Infrared Spectrometer
(CIRS) data taken during Titan flybys from 2004-2010 and to the 1980 Voyager 1 flyby
values inferred from the re-analysis of the Infrared Radiometer Spectrometer (IRIS) spectra
[1], as well as to the intervening ground- and space- based observations (such as with ISO,
[2]), providing us with a new view of the stratospheric evolution over a Titanian year
(V1 encounter Ls=9° was reached in mid-2010). CIRS nadir and limb spectral
[3,4] show variations in temperature and chemical composition in the stratosphere
during the Cassini mission, before and after the Northern Spring Equinox (NSE). We
find indication for a weakening of the temperature gradient with warming of the
stratosphere and cooling of the lower mesosphere. In addition, we infer precise
concentrations for the trace gases and their main isotopologues and find that the
chemical composition in Titan’s stratosphere varied significantly with latitude during
the 6 terrestrial years investigated here, with increased mixing ratios towards the
northern latitudes. In particular, we find a maximum enhancement of several gases
observed at northern latitudes up to 50°N around mid-2009, at the time of the NSE.
We find that this raise is followed by a rapid decrease in chemical inventory in
2010 probably due to changes in the cross vortex mixing or northward migration of
the vortex boundary [5,6,7] consistent with the weakening thermal gradient. The
finding also ties into the location of the maximum temperature gradient, which
appears to be moving northward over the winter/spring season. The return of today’s
abundances close to the Voyager values (at the same season) is an indication that, as
for the Earth, the solar radiation dominates over the other energy sources even at
10AU [8]. Nevertheless, the differences observed for some complex hydrocarbons
in the North pole indicate that the other processes could be at play as well, for
example the variability of the solar insolation itself through the 11-year solar cycle.
We show indeed that wrt V1 the stratospheric composition shows higher values
near the northern fall equinox (1997) and lower ones at the spring equinox (2009).
An additional cause could be spatial changes (due to Titan’s inclination) in the
energy input to Titan’s atmosphere as a driver for changes in the advection patterns,
circulation, etc which eventually provide a stronger variability in the latitudinal
abundances of photochemical species. Circulation and photochemical models must
satisfy the constraints set by these results, but further observations will have to
come from the next summer solstice (2017) and for a complete new Titan year in
2027.
References: [1] Coustenis, A., Bézard, B., Icarus 115, 126, 1995. [2] Coustenis, A., et al.,
Icarus 161, 383, 2003. [3] Coustenis, A., et al., Icarus 207, 461, 2010. [4] Vinatier, S., et al.,
Icarus, 205, 559, 2010. [5] Bampasidis et al., ApJ, 760, 144, 2012. [6] Teanby et al.,
Astrophys. J. 724, L84–L89 (2010). [7] Teanby et al., Nature, 491, 732, 2012, [8] Coustenis,
A., et al., in preparation, 2013. |
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