Alessandro Morbidelli (OCA, Nice) Kevin Walsh (SWRI, Boulder) Sean Raymond (CNRS, Bordeaux)
S. Bougher and A. Brecht (U. of Michigan) S. Rafkin and A. Stern (SwRI-Boulder)
description
Transcript of S. Bougher and A. Brecht (U. of Michigan) S. Rafkin and A. Stern (SwRI-Boulder)
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VTGCM 1Rafkin et al
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: [email protected] or [email protected]
This work was funded in part by the NASA Venus Express Participating Scientist Program under grant NNG06GC76G.
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VTGCM 2Rafkin et al
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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VTGCM 3Rafkin et al
Venus Atmosphere Regions and Processes
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VTGCM 4Rafkin et al
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 5Rafkin et al
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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VTGCM 6Rafkin et al
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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VTGCM 7Rafkin et al
T+(U,V) at Exobase
VEX PVO
U<185 m/sT<230K U<220 m/sT<300K
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VTGCM 8Rafkin et al
Temperature (K) at Equator
VEX PVO
T(DY)<230KT(NT)>100K T(DY)<300KT(NT)>100K
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VTGCM 9Rafkin et al
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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VTGCM 10Rafkin et al
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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VTGCM 11Rafkin et al
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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VTGCM 12Rafkin et al
Electron Density (#/cm3) at Equator(VEX): log10[Ne]
[Ne] < 4.0x 105Peak [Ne]Density
@ ~138 km.
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VTGCM 13Rafkin et al
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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VTGCM 14Rafkin et al
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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VTGCM 15Rafkin et al
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.