J/A+A/641/A116 Titan middle atmosphere thermal field (Vinatier+, 2020)
Temperature and chemical species distributions in the middle atmosphere observed
during Titan's late northern spring to early summer.
Vinatier S., Mathe C., Bezard B., Vatant d'Ollone J., Lebonnois S.,
Dauphin C., Flasar F.M., Achterberg R.K., Seignovert B., Sylvestre M.,
Teanby N.A., Gorius N., Mamoutkine A., Guandique E., Jennings D.E.
<Astron. Astrophys. 641, A116 (2020)>
=2020A&A...641A.116V 2020A&A...641A.116V (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Planets ; Abundances
Keywords: planets and satellites: individual: Titan -
planets and satellites: atmosphere -
planets and satellites: composition - method: data analysis -
radiative transfer - infrared: planetary systems
Abstract:
We present a study of the seasonal evolution of Titan's thermal
field and distributions of haze, C2H2, C2H4, C2H6,
CH3C2H, C3H8, C4H2, C6H6, HCN, and HC3N from March
2015 (Ls=66°) to September 2017 (Ls=93°) (i.e., from the last
third of northern spring to early summer). We analyzed thermal
emission of Titan's atmosphere acquired by the Cassini Composite
Infrared Spectrometer (CIRS) with limb and nadir geometry to retrieve
the stratospheric and mesospheric temperature and mixing ratios
pole-to-pole meridional cross sections from 5mbar to 50ubar
(120-650km). The southern stratopause varied in a complex way and
showed a global temperature increase from 2015 to 2017 at
high-southern latitudes. Stratospheric southern polar temperatures,
which were observed to be as low as 120K in early 2015 due to the
polar night, showed a 30K increase (at 0.5mbar) from March 2015 to May
2017 due to adiabatic heating in the subsiding branch of the global
overturning circulation. All photochemical compounds were enriched at
the south pole by this subsidence. Polar cross sections of these
enhanced species, which are good tracers of the global dynamics,
highlighted changes in the structure of the southern polar vortex.
These high enhancements combined with the unusually low temperatures
(<120K) of the deep stratosphere resulted in condensation at the south
pole between 0.1 and 0.03mbar (240-280km) of HCN, HC3N, C6H6 and
possibly C4H2 in March 2015 (Ls=66°). These molecules were
observed to condense deeper with increasing distance from the south
pole. At high-northern latitudes, stratospheric enrichments remaining
from the winter were observed below 300km between 2015 and May 2017
(Ls=90°) for all chemical compounds and up to September 2017
(Ls=93°) for C2H2, C2H4, CH3C2H, C3H8, and
C4H2. In September 2017, these local enhancements were less
pronounced than earlier for C2H2, C4H2, CH3C2H, HC3N,
and HCN, and were no longer observed for C2H6 and C6H6, which
suggests a change in the northern polar dynamics near the summer
solstice. These enhancements observed during the entire spring may be
due to confinement of this enriched air by a small remaining winter
circulation cell that persisted in the low stratosphere up to the
northern summer solstice, according to predictions of the Institut
Pierre Simon Laplace Titan Global Climate Model (IPSL Titan GCM). In
the mesosphere we derived a depleted layer in C2H2, HCN, and
C2H6 from the north pole to mid-southern latitudes, while
C4H2, C3H4, C2H4, and HC3N seem to have been enriched in
the same region. In the deep stratosphere, all molecules except
C2H4 were depleted due to their condensation sink located deeper
than 5mbar outside the southern polar vortex. HCN, C4H2, and
CH3C2H volume mixing ratio (VMR) cross section contours showed
steep slopes near the mid-latitudes or close to the equator, which can
be explained by upwelling air in this region. Upwelling is also
supported by the cross section of the C2H4 (the only molecule not
condensing among those studied here) volume mixing ratio observed in
the northern hemisphere. We derived the zonal wind velocity up to
mesospheric levels from the retrieved thermal field. We show that
zonal winds were faster and more confined around the south pole in
2015 (Ls=67-72°) than later. In 2016, the polar zonal wind speed
decreased while the fastest winds had migrated toward low-southern
latitudes.
Description:
Each file contains a vertical profile of one Titan's atmospheric
parameter (temperature; volume mixing ratio of C2H2, C2H4,
C2H6, C3H8, C3H4, C4H2, C6H6, HCN, HC3N; mass
mixing ratio of haze or extinction coefficient of haze), which are
displayed in the figures of the paper.
Header of each file gives the observation characteristics of each
retrieved vertical profiles. The method used to retrieve the vertical
profiles is described in the paper.
Files names include:
- the main observing parameters (Solar Longitude = Ls, Latitude = lat,
Longitude = lon)
- the atmospheric parameter name: "profT" corresponds to thermal
profiles; "profq" followed by a species name corresponds to the
volume mixing ratio profile of the molecule or the mass mixing ratio
of the haze; "kext" corresponds to the extinction coefficient
profile of the haze.
- a reference to the paper (VINATIER2020).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 75 12 List of repertories
profT/* . 169 Individual thermal profiles
kext_HAZE/* . 151 Individual extinction coefficient profile of
the haze
profq_C2H2/* . 159 Individual vertical profile of volume mixing
ratio of C2H2
profq_C2H4/* . 157 Individual vertical profile of volume mixing
ratio of C2H4
profq_C2H6/* . 159 Individual vertical profile of volume mixing
ratio of C2H6
profq_C3H4/* . 156 Individual vertical profile of volume mixing
ratio of C3H4
profq_C3H8/* . 139 Individual vertical profile of volume mixing
ratio of C3H8
profq_C4H2/* . 159 Individual vertical profile of volume mixing
ratio of C4H2
profq_C6H6/* . 159 Individual vertical profile of volume mixing
ratio of C6H6
profq_HC3N/* . 159 Individual vertical profile of volume mixing
ratio of HC3N
profq_HCN/* . 159 Individual vertical profile of volume mixing
ratio of HCN
profq_HAZE/* . 151 Individual vertical profile of mass mixing ratio
of haze
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Rep Repertory name
12- 75 A64 --- Title Explanation for the files in Rep
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): profT/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.2 km Alt Altitude
14- 24 E11.6 mbar Pres Pressure
29- 34 F6.2 K T Temperature
44- 49 F6.2 K b_T Minumim temperature (G1)
53- 58 F6.2 K B_T Maximum temperature (G1)
62 I1 --- sigma [0/2] sigma (G2)
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): kext_HAZE/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.2 km Alt Altitude
14- 24 E11.6 mbar Pres Pressure
29- 39 E11.6 cm-1 kext extinction coefficient of haze
44- 54 E11.6 cm-1 b_kext Minumim extinction coefficient of haze (G1)
59- 69 E11.6 cm-1 B_kext Maximum extinction coefficient of haze (G1)
74 I1 --- sigma [0/2] sigma (G2)
81- 86 F6.2 K AT Atmospheric temperature
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): profq_C*/* profq_HC*/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.2 km Alt Altitude
14- 24 E11.6 mbar Pres Pressure
29- 39 E11.6 --- q(VMR) Volume Mixing Ratio of the given molecule
44- 54 E11.6 --- b_q(VMR) Minumim Volume Mixing Ratio of the given
molecule (G1)
59- 69 E11.6 --- B_q(VMR) Maximum Volume Mixing Ratio of the given
molecule (G1)
74 I1 --- sigma [0/2] sigma (G2)
81- 86 F6.2 K T Temperature
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): profq_HAZE/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.2 km Alt Altitude
14- 24 E11.6 mbar P Pressure
29- 39 E11.6 --- q Mass Mixing Ratio of the haze
44- 54 E11.6 --- b_q Minumim Mass Mixing Ratio of the haze (G1)
59- 69 E11.6 --- B_q Maximum Mass Mixing Ratio of the haze (G1)
74 I1 --- sigma [0/2] sigma (G2)
81- 86 F6.2 K T Temperature
--------------------------------------------------------------------------------
Global notes:
Note (G1): minimum and maximum values of the atmospheric parameter corresponding
to "sigma" error bar.
Note (G2): sigma value as follows:
0 = a priori
1 = 1-sigma error
2 = 2-sigma upper limit
--------------------------------------------------------------------------------
Acknowledgements:
Sandrine Vinatier, Sandrine.Vinatier(at)obspm.fr
(End) Patricia Vannier [CDS] 31-Aug-2020