J/ApJ/724/L84 Changes in Titan's atmosphere from Cassini (Teanby+, 2010)
Seasonal changes in Titan's polar trace gas abundance observed by Cassini.
Teanby N.A., Irwin P.G.J., de Kok R., Nixon C.A.
<Astrophys. J., 724, L84-L89 (2010)>
=2010ApJ...724L..84T 2010ApJ...724L..84T
ADC_Keywords: Planets ; Spectra, infrared
Keywords: planets and satellites: atmospheres
Abstract:
We use a six-year data set (2004-2010) of mid-infrared spectra
measured by Cassini's Composite InfraRed Spectrometer to search for
seasonal variations in Titan's atmospheric temperature and
composition. During most of Cassini's mission Titan's northern
hemisphere has been in winter, with an intense stratospheric polar
vortex highly enriched in trace gases, and a single south-to-north
circulation cell. Following northern spring equinox in mid-2009,
dramatic changes in atmospheric temperature and composition were
expected, but until now the temporal coverage of polar latitudes has
been too sparse to discern trends. Here, we show that during equinox
and post-equinox periods, abundances of trace gases at both poles have
begun to increase. We propose that increases in north polar trace
gases are due to a seasonal reduction in gas depletion by horizontal
mixing across the vortex boundary. A simultaneous south polar
abundance increase suggests that Titan is now entering, or is about to
enter, a transitional circulation regime with two branches, rather
than the single branch circulation pattern previously observed.
Description:
We analyze a six-year time series of data from Cassini's Composite
InfraRed Spectrometer (CIRS) covering 2004 July to 2010 July. CIRS is
a Fourier transform spectrometer covering the spectral range
10-1500cm-1, with an adjustable spectral resolution of 0.5-15cm-1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 88 1050 Average temperature and composition derived from
104 individual observation sequences
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See also:
J/ApJS/191/96 : IR spectra and optical constants of ices (Moore+, 2010)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Parameter Temperature or gas abundance (1)
14- 16 I3 deg Lat Latitude
18- 25 F8.2 --- 2004.75 ? Average Value between 2004.50 and 2005.00
27- 34 F8.2 --- 2005.38 ? Average Value between 2005.00 and 2005.75
36- 43 F8.2 --- 2006.12 ? Average Value between 2005.75 and 2006.50
45- 52 F8.2 --- 2007.00 Average Value between 2006.50 and 2007.50
54- 61 F8.2 --- 2008.00 Average Value between 2007.50 and 2008.50
63- 70 F8.2 --- 2008.75 Average Value between 2008.50 and 2009.00
72- 79 F8.2 --- 2009.30 Average Value between 2009.00 and 2009.60
81- 88 F8.2 --- 2010.10 ? Average Value between 2009.60 and 2010.60
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Note (1): Data covers latitudes 85°S--85°N in 5 deg steps for all
gases and temperatures at 0.7 and 0.07mbar. Temperatures are in Kelvin
and gas abundances are in parts per billion. Values beginning with "s"
are the error weighted standard error of the points in each time bin
while values beginning with "n" are the number of individual
retrievals in each bin.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 06-Aug-2012