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VTGCM and Applications to VEX and PVO Data Analysis:Upgraded Simulations (F10.7 ~70 & 200)

Venus Express Science MeetingThuile, 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.

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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 (O2 airglow, T structure, inferred winds)

-- VMC (visible and IR camera, O2 airglow)

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Venus Atmosphere Regions and Processes

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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, N2, CO2, Z PCE ions Fields: CO2+, O2+, N2+, NO+, O+, Ne Minor Fields: O2 (and O2 IR nightglow at 1.27 m) Future Minor Fields: N(4S), N(2D) (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: O2-IR, NO-UV(future)

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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.

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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-CO2) = 3.0 x 10-12 cm3/sec at 300K CO2 15- m cooling scheme from Bougher et al., (1986). Kzz ≤ 1.0-3.0 x107 cm2/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)

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T+(U,V) at Exobase

VEX PVO

U<185 m/sT<230K U<220 m/sT<300K

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Temperature (K) at Equator

VEX PVO

T(DY)<230KT(NT)>100K T(DY)<300KT(NT)>100K

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Solar Cycle Texo & T140Variations(LAT = 2.5N; SLT = 1200)

T140 ~ 200 to 240KF10.7 ~ 70 to 240 units

* PVO

*MGN

Texo ~ 230 to 325K F10.7 ~ 70 to 240 units

ΔTexo ~ 95 K

*VEX?

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U and W at Equator

VEX PVO

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

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Concentration (#/cm3) at Equator

NightsidePeak:

6.0x1011 cm-3

NightsidePeak:

7.9x1011 cm-3

NightsidePeak:

6.7x1012 cm-3

NightsidePeak:

7.7x1012 cm-3

VEX

PVO

log10[O] log10[CO] log10[CO2]

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Electron Density (#/cm3) at Equator(VEX): log10[Ne]

[Ne] < 4.0x 105Peak [Ne]Density

@ ~138 km.

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Peak Electron Density Variations(LAT = 2.5N; SLT = 12; ALT ~ 140 km)

SMIN = 4.1 x 105 cm3/secSMAX = 7.0 x 105 cm3/sec

* PVO

*Venera 9-10

*VEX?

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Molecular O2 at Equator

log10[O2] #/cm3Molecular O2 IR

Nightglow at Equator (log10 (ph/cm3/sec)

Peak V.E.R.of

7.7x105 ph/cm3/sec@ 108 km.

Peak Intensity:

~0.8-1.0 MR

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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.

O2 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 O2 and NO nightglow intensity distributions.