NON-MONOTONIC EDDY DIFFUSION PROFILE OF TITAN’S ATMOSPHEREA Revision from Cassini Observations

Cheng Li1, X. Zhang1, J. A. Kammer1, M. C. Liang2, Y. L. Yung1

1California Institute of Technology2Research Center for Environmental Changes, Academia Sinica, Taiwan

Photochemistry on Titan

CH4 N2

CH,1CH2,3CH2

CH3

C2H2, C2H4,C2H6

C2H,C2H3,…

C3Hx, C4Hx,…

e-

N2+,N,N+

surface

2

𝑃 −𝐿=− 𝜕𝜕 𝑧 (𝐾 𝑛𝜕𝑥𝜕 𝑧 )

3

Chemical production

Chemical loss

Vertical transport

Eddy diffusivity

Mixing ratio

One dimensional photochemical model

4

C2H2 formation/destruction pathway

5

CIRS limb view and FUV stellar occultationA

ltitu

de

(km

)

CH4

C2H2 C2H4 C2H6

CH3CCH C3H8 C4H2 C6H6

Mixing ratio Vinatier et al., 2009; Kammer et al., 2011

Vinatier et al., 2009; Kammer et al., 2011;

6

No CH4 escape, Koo = 108 cm2 s-1

7

Levenberg–Marquardt

Mixing ratioal

titud

e

C2H2

1000

Retrieval algorithm

8

Molecular diffusivity

Initial guess

Retrieved eddy diffusivity

H2 and C2-hydrocarbons

Higher hydrocarbons

11

Newly detected C3H6

12

Conclusion

13

Back up slides

Dashed Red: CH4 escape = 109 cm-2s-1

Koo = 1.5 x 107cm2s-1

Solid Red:CH4 escape = 0Koo = 1 x 108 cm2s-1

CH4 escape

15

New reaction rate constants (solid lines)

604K / 511K / 400K / 285K / 170K (Titan)

Moses et al.,2000This work

Lightfoot et al., 1987

H + C2H4 + M C2H5 + M