Seasonal effects in Titan s stratosphere analyzed through ...lasp.colorado.edu/media/projects/cassini/meetings/css2018/3-WEDNES… · Results - Seasonal effects in the stratosphere

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

mailto: [email protected]

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



Seasonal evolution - winter polar vortex



Recent works - South polar vortex



Recent works - Condensates at South Pole

Courtesy : S. Vinatier


Modelling stratosphere within IPSL Titan’s GCM

Table of contents






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



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 ) ...



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


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)


Results - Seasonal effects in the stratosphere

Table of contents






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



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 ).



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 ?


Results - Seasonal effects in the stratosphere Seasonal thermal structure

Seasonal behaviour of the thermal structure


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


Results - Seasonal effects in the stratosphere Seasonal enrichment variations

Seasonal behaviour of HCN



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 !



Seasonal behaviour of C2H2



Seasonal behaviour of C6H6



Seasonal behaviour of HC3N



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.


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



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 ...



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 )


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.



Thanks for your attention !

Images courtesy : NASA/JPL



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.


Documents

Seasonal effects in Titan s stratosphere analyzed through ...lasp.colorado.edu/media/projects/cassini/meetings/css2018/3-WEDNES… · Results - Seasonal effects in the stratosphere