1. Modeling the Distribution of H 2 O and HDO in the upper atmosphere of Venus Mao-Chang Liang Research Center for Environmental Changes, Academia Sinica C. D. Parkinson (U. of Michigan), S. Bougher (U. of Michigan), A. Brecht (U. of Michigan), S. Rafkin (SwRI Boulder), B. Foster (NCAR HAO), Y. L. Yung (Caltech) 2008 EGU Conference at Vienna, Austria (April 14-18)

2. Photochemical modeling 1-D and 2-D Catech/JPL KINETICS Cloud top at 58 km to 112 km 24 species including chlorine, hydrogen, oxygen, and carbon compounds 210 chemical reactions Transport by eddy mixing (1-D) and eddy mixing + advection (2-D) –Homopause >> 112 km Advection –Downwelling at -0.3 cm s -1 : 75-85 km –Upwelling at 0.5 cm s -1 : 85-95 km –Downwelling at -0.5 cm s -1 : >95 km

3. Chemical fractionation Water photolysis –H 2 O + h  H + OH –HDO + h  H + OD or D + OH Hydrogen chloride photolysis –HCl + h  H + Cl –DCl + h  D + Cl

4. Photoabsorption cross sections

5. Dynamical fractionation Hydrogen escape (Gurwell and Yung 1993) –H escape: 3.5  10 6 atoms cm -2 s -1 –D escape: 3.1  10 4 atoms cm -2 s -1 H production rate –HCl photolysis: 8.1  10 10 atoms cm -2 s -1 –H 2 O photolysis: 4.8  10 8 atoms cm -2 s -1

6. 1-D model results 0 -0.3 0.5 -0.5 advection

7. Photochemistry at 75-85 km d[H 2 O]/dt = -J H2O * [H 2 O] d[HDO]/dt = -J HDO * [HDO] R = { HDO(t)/H 2 O(t) } / { HDO(0)/H 2 O(0) } = exp[(J H2O - J HDO )t] r = H 2 O(t) / H 2 O(0) = exp(-J H2O t) R = r -f, f = (J H2O - J HDO )/J H2O = 0.46

9. 2-D model results

10. Estimate of downwelling Diabatic heating by air subsidence –  T = -w(  T/  z +  T/H)  t  = (  -1)  = 1/4 (  =Cp/Cv) –  t = t rad ~ 3 day –T = 175 K,  T/  z = -4 K/km, H = 4 km –  T ~ -18w –w ~ 1 cm s -1 –Needed to explain the increase of H 2 O above 95 km

11. Temperature field

12. Vertical wind

13. Summary If the decrease of H 2 O mixing ratio at ~75 km is caused by photolysis, the isotopic compostion can be explained by photolytic fractionation Inferred downwelling is explained by NO influx in the polar region Inferred upwelling remains unknown

14. Thank you

15. UPDATE  Re-vitalized National Center for Atmospheric Research (NCAR) thermospheric general circulation model for Venus (VTGCM);  Lowered the bottom boundary (from ~95km to ~80km) to insure all dynamical influences contributing to the NO and O 2 nightglow layers can be captured;  Applied new Near-IR heating and CO 2 15-micron cooling rates (Roldan et al, 2000);  Analyzed solar cycle variations (F10.7 = 70 to 200)  Used observations from Pioneer Venus Orbiter (PVO) and Venus Express (VEX), including measurements of NO, O 2, and H airglows plus temperatures. Interpreted these global tracers of the thermospheric circulation with the VTGCM;  Goal: To determine the dynamical processes that link the Venus middle and upper atmospheres through general circulation modeling of the upper mesosphere and thermosphere.

16. Venus Thermospheric General Circulation Model (VTGCM): Current Formulation and Structure  Altitude range: ~80-200 km (day); ~80-150 km (night)  Horizontal resolution: 5x5º latitude-longitude grid (pole-to-pole)  Pressure vertical coordinate (1/2-H intervals): 46-levels  Major Fields: T, U, V, W, O, CO, N 2, CO 2, Z  PCE ions Fields: CO 2 +, O 2 +, N 2 +, NO+, O+, Ne  Minor Fields: O 2 (and O 2 IR nightglow at 1.27  m)  Future Minor Fields: N( 4 S), N( 2 D) (and NO nightglow)  Full 2-hemispheric capability. Timestep = 30.0 secs.  Venus obliquity ~ 177.4º (“seasonal” cases possible)  Rayleigh friction used to slow SS-AS winds.  Upgraded airglow capability: O 2 -IR, NO-UV(future)