1. Rafkin et al VTGCM1 VTGCM and Applications to VEX and PVO Data Analysis: Upgraded Simulations (F10.7 ~70 & 200) Venus Express Science Meeting Thuile, Italy March 18-24, 2007 S. Bougher and A. Brecht (U. of Michigan) S. Rafkin and A. Stern (SwRI-Boulder) Contact: rafkin@boulder.swri.edu or bougher@umich.edu This work was funded in part by the NASA Venus Express Participating Scientist Program under grant NNG06GC76G.

2. Rafkin et al VTGCM2 Upper Atmosphere Datasets at Venus  Pioneer Venus Orbiter (1979-1992) -- F10.7 ~ 200 (in-situ at start) and 130 (entry at end) -- OUVS (airglow, neutral density and T structure) -- ONMS (neutral density and T structure) -- OETP (electron T and density) -- RPA (ion T and density)  Venus Express (June 2006 to date) -- F10.7 ~ 70-90 (primary mission) -- SPICAV (airglow, neutral density and T structure) -- VeRA (radio occultation; T-structure; electron density profiles) -- VIRTIS (O 2 airglow, T structure, inferred winds) -- VMC (visible and IR camera, O 2 airglow)

3. Rafkin et al VTGCM3 Venus Atmosphere Regions and Processes

4. Rafkin et al VTGCM4 Venus Thermospheric General Circulation Model (VTGCM) Formulation and Structure  Altitude range: ~94-200 km (day); 94-150 km (night)  5x5º latitude-longitude grid (pole-to-pole)  Pressure vertical coordinate (1/2-H intervals): 34-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 = 60.0 secs.  Venus obliquity ~ 177.4º (“seasonal” cases possible)  Rayleigh friction used to slow SS-AS winds.  Weak RSZ winds prescribed at model lower boundary  Upgraded airglow capability: O 2 -IR, NO-UV(future)

5. Rafkin et al VTGCM5 VTGCM Science Goals in Support of VEX  Compare the modeled structure of the atmosphere (up to 180 km) with high vertical resolution solar/stellar occultations, especially in middle to high latitudes;  Use observed spatial distributions of NO, O, and H airglows, at spatial resolutions substantially better than existing data, and interpret these global tracers of the thermospheric circulation with the VTGCM;  Determine the dynamical processes that link the Venus middle and upper atmospheres (tides, planetary, and gravity waves, etc.) through general circulation modeling of the thermosphere;  Compare and contrast the response of the Venus atmosphere with that of Mars—where the sister spacecraft (Mars Express) and SPICAM is in orbit, and where the Mars Reconnaissance Oribiter was simultaneously aerobraking in 2006—under the same solar cycle forcing.

6. Rafkin et al VTGCM6 Input Parameters for VTGCM Simulations: VEX & PVO  F10.7 ~ 70, 130, 200. Solomon UV routine (0.1-175.0 nm).  Factor for heliocentric distance = 1.914. Equinox (only).  Q-Efficiency (EUV, UV) = 20, 22% (after Fox, 1988)  Slant column integration for Chapman functions.  K(O-CO 2 ) = 3.0 x 10 -12 cm 3 /sec at 300K  CO 2 15-  m cooling scheme from Bougher et al., (1986).  K zz ≤ 1.0-3.0 x10 7 cm 2 /sec. Prandtl # = 10.0  Fox & Sung (2001) ion-neutral chemical reactions & rates.  O & CO sources and losses explicitly calculated.  Te from Theis and Brace (1993). Ti = Tn.  No Venus rotation. Static (GM) LBC (densities and T)

7. Rafkin et al VTGCM7 T+(U,V) at Exobase VEXPVO U<185 m/sT<230KU<220 m/sT<300K

8. Rafkin et al VTGCM8 Temperature (K) at Equator VEXPVO T(DY)<230KT(NT)>100KT(DY)<300KT(NT)>100K

9. Rafkin et al VTGCM9 Solar Cycle T exo & T 140 Variations (LAT = 2.5N; SLT = 1200) T 140 ~ 200 to 240K F10.7 ~ 70 to 240 units * PVO * MGN Texo ~ 230 to 325K F10.7 ~ 70 to 240 units ΔTexo ~ 95 K *VEX?

10. Rafkin et al VTGCM10 U and W at Equator VEXPVO U (m/s) W (s -1 ) (Multiply By SHT for m/s) Min: -0.35 m/s Max: 0.25 m/s Min: -186 m/s Max: 173 m/s Min: -220 m/s Max: 200 m/s Min: -0.6 m/s Max: 0.45 m/s

11. Rafkin et al VTGCM11 Concentration (#/cm 3 ) at Equator Nightside Peak: 6.0x10 11 cm -3 Nightside Peak: 7.9x10 11 cm -3 Nightside Peak: 6.7x10 12 cm -3 Nightside Peak: 7.7x10 12 cm -3 VEX PVO log10[O]log10[CO]log10[CO 2 ]

12. Rafkin et al VTGCM12 Electron Density (#/cm 3 ) at Equator (VEX): log10[Ne] [Ne] < 4.0x 10 5 Peak [Ne] Density @ ~138 km.

13. Rafkin et al VTGCM13 Peak Electron Density Variations (LAT = 2.5N; SLT = 12; ALT ~ 140 km) SMIN = 4.1 x 10 5 cm 3 /sec SMAX = 7.0 x 10 5 cm 3 /sec * PVO * Venera 9-10 *VEX?

14. Rafkin et al VTGCM14 Molecular O 2 at Equator log10[O 2 ] #/cm 3 Molecular O 2 IR Nightglow at Equator (log10 (ph/cm 3/ sec) Peak V.E.R. of 7.7x10 5 ph/cm 3 /sec @ 108 km. Peak Intensity: ~0.8-1.0 MR

15. Rafkin et al VTGCM15 Summary and Conclusions  Upgraded VTGCM code is operational for 4-major and 1-minor species plus several photochemical ion species.  Production simulations over the solar cycle (and weak Venus seasons) are completed. Comparisons to PVO, Magellan drag (MGN), and VEX datasets are starting.  O 2 IR nightglow calculations are available for new comparisons to VEX datasets (when available).  Gravity wave breaking formulations will be soon incorporated into the VTGCM: (a) to provide self- consistent RSZ winds and needed momentum drag, and (b) to produce unique circulation patterns giving rise to variable O 2 and NO nightglow intensity distributions.