Seasonal effects in Titan’s stratosphere analyzed throughGlobal Climate ModellingJ.Vatant d’Ollone, S.Lebonnois, M.Sylvestre, S.Vinatier, J.BurgalatCassini Science Symposium - August 15th, 2018 - Boulder CO8 [email protected] - LMD/IPSL, Sorbonne Université, Paris
Table of contents
1 Motivations and background - Titan seasonalevolution
2 Modelling stratosphere within IPSL Titan’s GCMRecent improvements in Titan modelConsequences
3 Results - Seasonal effects in the stratosphereLow stratosphereSeasonal thermal structureSeasonal enrichment variations
4 Conclusions and outlooksWhat’s next ?Take-Home
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 2 / 29
Motivations and background - Titan seasonal evolution
Seasonal evolution
Courtesy : S. Vinatier
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 3 / 29
Motivations and background - Titan seasonal evolution
Seasonal evolution - winter polar vortex
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 4 / 29
Motivations and background - Titan seasonal evolution
Recent works - South polar vortex
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 5 / 29
Motivations and background - Titan seasonal evolution
Recent works - Condensates at South Pole
Courtesy : S. Vinatier
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 6 / 29
Modelling stratosphere within IPSL Titan’s GCM
Table of contents
1 Motivations and background - Titan seasonalevolution
2 Modelling stratosphere within IPSL Titan’s GCMRecent improvements in Titan modelConsequences
3 Results - Seasonal effects in the stratosphereLow stratosphereSeasonal thermal structureSeasonal enrichment variations
4 Conclusions and outlooksWhat’s next ?Take-Home
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 7 / 29
Modelling stratosphere within IPSL Titan’s GCM Recent improvements in Titan model
LMD Titan’s GCM suffered from limitations
(Lebonnois et al., 2012)
• Temperature profiles diverged atthe ceiling of the model
• Long-term runs lead to a strongstability zone, "stucking" theHadley cell
• Limited vertical mixing ofstratospheric compounds
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 8 / 29
Modelling stratosphere within IPSL Titan’s GCM Recent improvements in Titan model
New set-up for Titan GCM
• Correlated-k scheme with CH4, C2H6, C2H2 and HCN from HITRAN2012 ( + Reims GSMA methane line database in 7900-12000 cm−1
range ) + Collision-induced absorption (N2, H2 and CH4)• Aerosol mean opacity profile based on constraints retrieved from DISR
data [Lavvas et al., 2010]• Photochemical solver ( Lebonnois et al. 2001, Crespin et al. 2008 ) up
to 1300 km, 44 species (H,C,N) and 344 photochemical reactions
So far it implied to decouple radiative transfer from microphysics ( nolatitudinal or temporal variations ) ...
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 9 / 29
Modelling stratosphere within IPSL Titan’s GCM Recent improvements in Titan model
Radiative transfer extinctions (m−1) update
101 102 103 104
Wavenumber (cm−1 )
10-1
100
101
102
103
104
105
Pressure (Pa)
2e+01
1e-02
1e-10
1e-06
1e-14
101 102 103 104
Wavenumber (cm−1 )
10-1
100
101
102
103
104
105
Pressure (Pa)
2e+01
1e-02
1e-10
1e-06
1e-14
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 10 / 29
Modelling stratosphere within IPSL Titan’s GCM Consequences
Main consequence - Simulated stratopause
60 80 100 120 140 160 180 200 220 240Temperature (K)
10-1
100
101
102
103
104
105
106
Pre
ssure
(Pa)
This study - Ls =240 ◦ - Equator
This study - Ls =240 ◦ - 60 ◦ N
This study - Ls =240 ◦ - 75 ◦ N
HASI (Huygens)
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 11 / 29
Results - Seasonal effects in the stratosphere
Table of contents
1 Motivations and background - Titan seasonalevolution
2 Modelling stratosphere within IPSL Titan’s GCMRecent improvements in Titan modelConsequences
3 Results - Seasonal effects in the stratosphereLow stratosphereSeasonal thermal structureSeasonal enrichment variations
4 Conclusions and outlooksWhat’s next ?Take-Home
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 12 / 29
Results - Seasonal effects in the stratosphere Low stratosphere
Low stratosphere
120125130135140145150155 6 mbar
200720132016-2017
90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90Latitude
105110115120125130135140 15 mbar
200720132016-2017
Tem
pera
ture
(K)
Sylvestre et al., Submitted to Icarus
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 13 / 29
Results - Seasonal effects in the stratosphere Low stratosphere
Low stratosphere seasonal evolution
0 45 90 135 180 225 270 315 360Solar longitude ( )
5
6
7
8
9
10
20
30
40
50
Pres
sure
(mba
r)
GCM Temperatures at 70N
70
80
90
100
110
120
130
140
150
160
Tem
pera
ture
(K)
Sylvestre et al., Submitted to Icarus
• Pronounced asymetry betweeningress and egress of polarwinter consistent with CIRSobservations : It’s a (cold) trap !
• Under ' 25 mbar the seasonalcycle is damped due to radiativetimescales reachin 1 Titan year (cf Bézard et al. 2018 ).
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 14 / 29
Results - Seasonal effects in the stratosphere Low stratosphere
Winter "polar shoulder"
60 80 100 120 140 160 180 200Temperature (K)
10 1
100
101
102
103
Pressure (m
bar)
T27 - Θ=53 ∘ - Ls=329 ∘
GCM - Θ=53 ∘ - Ls=260 ∘
T31 - Θ=71 ∘ - Ls=331 ∘
GCM - Θ=71 ∘ - Ls=260 ∘
T57 - Θ=81 ∘ - Ls=358 ∘
GCM - Θ=81 ∘ - Ls=260 ∘
• Observed in radio-occultations (Schinder et al. 2012 )
• Quite reproduced in simulationswithout latitudinal or temporalvariations of composition !
• Drived by polar night lack ofinsolation (symmetric wrtsolstice) and radiative timescaletransition zone.
• Presence of clouds wouldcertainly sharpen thisdestabilization and enhance the"trap" in cold state.
• Are other Cassini radio-scienceprofiles available ?
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 15 / 29
Results - Seasonal effects in the stratosphere Seasonal thermal structure
Seasonal behaviour of the thermal structure
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 16 / 29
Results - Seasonal effects in the stratosphere Seasonal thermal structure
Thermal structure sum-up
• :-) Low-latitudes thermal profiles quite correct ( with stratopause ! )• :-( Lack of winter polar cooling since no retroaction of haze
accumulation• :-( Too warm and too low polar winter stratopause compared to CIRS
data• :-( Induced circulation weaker than expected and limited in vertical
extension during the heart of winter• :-) Low stratosphere destabilization ("polar shoulder") quite well
reproduced
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 17 / 29
Results - Seasonal effects in the stratosphere Seasonal enrichment variations
Seasonal behaviour of HCN
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 18 / 29
Results - Seasonal effects in the stratosphere Seasonal enrichment variations
Towards a high-altitude cloud ?
0 50 100 150 200 250 300 350Solar longitude
102
103
104
Pressure (P
a)
HCN
C6H6
C2H6
50 km
80 km
150 km
Normalized condensation rates at 80S
• Unlike Hourdin et al. 2004variations of temperature nowimpact condensation.
• De Kok et al. 2014 : HCN ice at300 km
• Vinatier et al. 2018 : C6H6 iceat 250 km
• With further cooling ( polarnight haze, cloud condensates )and better trace compoundsenrichment, we could maybereach 300 km !
• → We need a coupledmicrophysical model !
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 19 / 29
Results - Seasonal effects in the stratosphere Seasonal enrichment variations
Seasonal behaviour of C2H2
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 20 / 29
Results - Seasonal effects in the stratosphere Seasonal enrichment variations
Seasonal behaviour of C6H6
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 21 / 29
Results - Seasonal effects in the stratosphere Seasonal enrichment variations
Seasonal behaviour of HC3N
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 22 / 29
Results - Seasonal effects in the stratosphere Seasonal enrichment variations
Seasonal enrichment variations
• :-) Amplitude of variations in good agreement with CIRS data.• :-) Hints of high-altitude condensation.• :-( Reversal of polar enrichment occuring too early compared to the
observation because of the limited vertical extension of the circulationdue to lack of polar night haze cooling.
• :-) Small return cell above summer pole trapping some compounds.• ? ? High altitude equatorial depleted C6H6.• ? ? No real enrichment of HC3N above pole ? Linked to very short
lifetime ?• :-) High-altitude variations indicate that above winter pole,
abundances of photochemical products increase after spring equinoxaround 600-800 km altitude. With circulation more extended above350 km, this could be related to the increase observed in the polarenrichment after the equinox.
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 23 / 29
Conclusions and outlooks What’s next ?
Hadley cell vertical extension ?
−50 0 50Latitude ( ◦ )
10-3
10-2
10-1
100
101
102
103
104
105
Pre
ssure
(Pa)
-0.1
00
-0.100
-0.100
-0.100
-0.100
-0.0
30-0.030
-0.030
-0.030
-0.0
30
-0.030
-0.030
-0.0
10-0.010
-0.0
10
-0.0
10
-0.010-0.010
-0.010-0.010
-0.010
-0.010
-0.010
-0.0
10
-0.0
03-0.003
-0.003
-0.0
03
-0.003-0.003
-0.003-0.003-0.0
03-0.003
-0.003
-0.001-0.001
-0.001
-0.001
-0.001
-0.0
01
-0.001-0.0
01-0.001
-0.001
-0.001
0.0010.001
0.001
0.001
0.0
01
0.001
0.0
01
0.0010.0
01 0.001
0.001
0.001
0.0010.001
0.001
0.0030.003
0.0
030.003
0.0
03
0.003
0.003
0.0030.0
03 0.003
0.003
0.003
0.0030.003
0.003
0.0100.0100.010
0.0
10
0.010
0.010
0.010
0.010
0.010
0.010
0.010
0.010
0.0300.0300.030
0.030
0.030
0.030
0.0
30
0.030
0.030
0.030
0.030
0.1
000.100
0.1000.100
LS =12 ◦ - Zonal wind (m.s−1 ) - Streamfunction (109 kg.s−1 )
−15
0
15
30
45
60
75
90
105
−50 0 50Latitude ( ◦ )
10-3
10-2
10-1
100
101
102
103
104
105
Pressure (Pa)
-0.100
-0.100-0.100
-0.100
-0.100
-0.100
-0.030
-0.030-0
.030
-0.030
-0.030
-0.030
-0.010
-0.010
-0.010
-0.010
-0.010
-0.003
-0.003
-0.003
-0.003
-0.003
-0.001
-0.001
-0.001
-0.001
-0.001
-0.001
-0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.001
0.003
0.003
0.003
0.003
0.003
0.003
0.003
0.010
0.010
0.010
0.010
0.010 0.010
0.010
0.010
0.030
0.030
0.030
0.030
0.030 0.100
0.100
0.100
0.100
0.100
0.100
LS =20 ◦ - Zonal wind (m.s−1 ) - Streamfunction (109 kg.s−1 )
−20
0
20
40
60
80
100
120
140
160
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 24 / 29
Conclusions and outlooks What’s next ?
Towards an increased vertical extension
−50 0 50Latitude ( ◦ )
10-1
100
101
102
103
104
105
Pressure (Pa)
0.001
0.003
0.010
0.030
0.100
0.030
0.010
0.003
-0.001
0.001
0.100
0.100
0.3000.1
000.030
0.010
0.003
0.030 0
.100
0.300
-0.030
0.3000.300
0.010
0
30
60
90
120
150
180
• Motivations• With the improved
temperature profiles, Hadleycell could now vertically extent
• But ...• As long as we lack polar
cooling vertical circulation inwinter will be limited
• Thin layer approximation ! Weneed to use the deepatmosphere core (at 500 kmgg0' 0.6 ) !
• And also, non-LTE processes,illuminance over the poles ...
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 25 / 29
Conclusions and outlooks What’s next ?
What’s next ?
• A new bulk microphysical model for the haze ( work in progress withReims team )X Transport of the microphysical moments• Radiative coupling• Activate clouds formation
• Radiative impact of trace compounds variations (work in progress)• Run simulations with vertical increased extension ( implementation of
a deep atmosphere core for more accuracy )
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 26 / 29
Conclusions and outlooks Take-Home
Key take-home messages
• Radiative transfer scheme is now correct, giving an improved thermalstructure
• Lack of cooling above winter poles as long as no retroaction of hazeaccumulation ⇒ still limited vertical extension of circulation
• Once we have vertical extension of the Hadley cell ⇒ full view ofseasonal transport and enrichment of gazes and aerosols !
• "Polar shoulder" destabilization reproduced in the low stratospherewithout radiative feedback of haze or trace compounds !
• Enrichment in trace compounds (HCN,C2H2,C2H6 ... ) in goodagreement with CIRS data except for the delay at circulation reversal.
• High altitude condensation of HCN and C6H6 in the winter pole yetnot as much as in the observations.
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 27 / 29
Conclusions and outlooks Take-Home
Thanks for your attention !
Images courtesy : NASA/JPL
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 28 / 29
Conclusions and outlooks Take-Home
Temperature latitudinal contrast
(Schinder et al., 2012)65 70 75 80 85 90 95 100
Temperature (K)
103
104
105
Pressure (Pa)
This study - Ls =305 ◦ - Equator
This study - Ls =305 ◦ - 75 ◦
This study
- Without haze retroaction, temperature latitudinal contrast is fainterthan in the observations (Lebonnois et al, 2009)
- Too weak wind shear according to thermal wind equation in thetroposphere.
J. Vatant d’Ollone (LMD / IPSL) Titan’s stratosphere GCM August 15th, 2018 29 / 29