金星熱圏GCM(Hoshino et al., 2012, 2013)の確認と活用
Hiroki Karyua, Takeshi Kurodaa, Hideo Sagawab, Hitoshi Fujiwarac,
Masahiro Takagib, Yasumasa Kasabaa
a Tohoku University, b Kyoto Sangyo University, c Seikei University

2021/03/11

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Outline
qUpper atmospheric dynamics of Venus
qHoshino et al. (2012)
qHoshino et al. (2013)
qTest runs and applications

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Upper atmospheric dynamics of Venus

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Overview
q Different dynamical regimes
1. Retrograde superrotationg zonal wind (RSZ wind)
2. Subsolar-to-antisolar wind (SS-AS wind)Ø ~ 70 km → RSZ wind
Ø 70 ~ 120 km → transition region
Ø 120 km ~ SS-AS circulation
Transition region shows large variability
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Brecht et al., 20114

Observational studies : Nightglow
O2Center : antisolar pointNOO2 peak : 99 km
NO peak : 115 km→ different global
circulation pattern
99 km : Stable
115 km : Zonal wind

Maps of the statistical distribution of the O2 and NO night glow
[Soret et al., 2012, Stiepen et al., 2013]
Patchy structure indicates high variability of O2 and NO night glow intensity peak
→ variation in the background wind?
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Observational studies : Wave activity
q Periodic variations of oxygen EUV dayglow
in the thermosphere [Masunaga et al., 2015]

q Density oscillation in the nightside of
the thermosphere [Forbes and Konopliv, 2007]• 9 day period• 1.8, 2.8, 3.1, 4.5, and 9.9 day period
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Density oscillation of by planetary-scale
waves and/or gravity waves propagatingfrom the middle atmosphere?
6Summary of wind measurements~70 km : RSZ
70 ~ 120 km : Variable
120 ~ : SS-AS (& RSZ)
Schubert et al., 2007
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Outstanding problems
q Wind variations between 90 and 130 km regions
q Variable structures of NO and O2 nightglow emissions→ Non-steady transport of these species?
→ Influence of gravity waves?
q The role of wave activity

Hoshino et al. (2012) → Rossby wave, Kelvin wave, Thermal tides
Hoshino et al. (2013) → Gravity wave
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Hoshino et al. (2012)

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9Model description
q Basic settings•

5˚ in longitude x 10˚ in latitude,•38 vertical layers (80~180 km)•Chemical reactions (CO, CO2, O, O2)
Chemical reactions

2021/03/11•

1-D nightglow model→ calculated with 3-D composition distribution
obtained by the GCM→ comparison with previous observations
Recombination of atomic oxygen+10

Model description : Basic equations
q Momentum equations• Eddy viscosity• Molecular viscosity
𝜇 : Viscous coefficient𝜆!" : Rayleigh friction coefficientq Continuity equation• Rayleigh friction

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Model description : Energy conservation
q Energy conservation
1. Advectionvertical molecular heat conduction①

2. Vertical molecular heat conduction and eddy
heat transport②③④Molecular heat conduction coefficient

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3. Horizontal molecular heat conduction and eddy
heat transport
4. Work done by viscous force
5. Solar EUV heating, solar NIR heating, and CO2
15 µm radiative cooling12Model description : Boundary conditions
q Lower boundary• Fixed temperature and 0 wind velocity• [Case 1] Uniform geopotential height• [Case 2] Geopotential height fluctuation→ Wave effects
Similar manner to Bougher et al. (1993)

q Upper boundary• No temperature and horizontal
wind gradient2021/03/1113

Results
Zonal wind [m/s]Temperature [K]• SS-AS circulation driven by day-night temperature difference due to EUV heating(100 km ~)• Return flow below 90 km
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Effects of atmospheric waves
q Zonal wind average on the cordinates moving with the wave source• Thermal tides do not propagate vertically• Rossby wave propagates vertically but has
small amplitude• Kelvin wave propagates vertically and haslarge amplitudes(sometimes larger than 10 m/s)
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Nightglow distribution
q Averaged horizontal distribution of nightglow intensity** : without waves, ** : with waves• Approximately 4 day period fluctuation→ Period of Kelvin waves• Observed muximum intensity of 1.2 MR(Piccioni et al., 2009) is consistent with observation
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Kelvin wave would be the most plausible
cause for temporal variation in the nightglow
intensity and distribution
16

Hoshino et al. (2013)

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Model description(1)

q Same basic equations as Hoshino et al. (2012)
q Gravity wave parametarization• MK scheme [Medvedev and Klaassen, 2000]
Momentum deposition by gravity wave with wave number 𝑚

Convective dumping rate Horizontal wave nuber Power-spectral density→ maximum when 𝑐 = 𝑢(2)Total momentum deposition

q Lower boundary condition
1) Fixed zonal wind speed [0 and 40 m/s] (superrotation is considered)→ Center of the gravity wave phase velocity2) Power spectrum of gravity waves (vertical wave number)
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Results : Wind distribution
q Lower boundary 0 m/s
EQ

q Lower boundary 40 m/s
EQ

Zonal mean

• Symmetric structure with maximum
velocity around 240 m/s• Complex structure→ superposition of RSZ and SS-AS wind

• Strong deceleration around 125 km→ wave drag becomes stronger
above 125 km• RSZ wind driven by momentum deposition of gravity wave
→ gravity waves with fast phase velocity can reach high altitudes

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Results : Nightglow distribution
q Lower boundary 0 m/s•

q Lower boundary 40 m/s

Comparison with Hoshino et al. (2012)
RMS :Kelvin wave : 3 m/s
Gravity wave : 8 m/s

Gravity wave would cause stronger temporalvariation of the O2 nightglow
2021/03/11• Recent observation by VEX suggested no shift(Piccioni et al., 2009)→ gravity wave saturation should occur inhigher altitudes• Lower intensity because of less transport of O
from the dayside20Implication for wind observation
Zonal wind velocity at 110 km altitude
RSZ wind profile

Theoritical approach

theory110 kmsimulated• Theoritical estimation can cause large error
at 110 km (CO2 10 µm emmision altitude)
due to the asymmetricity of the wind field
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Summary of Hoshino et al. (2012, 2013)
q Hoshino et al. (2012)• Symmetric SS-AS circulation and the return flow below 90 km• Thermal tides : small amplitude, weak vertical propagation
Rossby waves : small amplitude, strong vertical propagation
Kelvin waves : large amplitude, strong vertical propagation• Kelvin wave would cause observed fluctuation of O2 nightglow emissionq Hoshino et al. (2013)• The gravity waves have an important role in controlling RSZ wind
• The gravity waves would cause larger fluctuation than that of Kelvin wave
• Theoritical estimation ≠ actual RSZ wind ?

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Test runs and applications

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Test runs of Hoshino et al. (2012, 2013)
q Hoshino et al., 2012Same feature but larger amplitude(without wave drag parameterization)

Same features and amplitudes
q Hoshino et al., 2013

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Applications
Upper mesosphere & Thermosphere

qCoupling with a photochemical modeltransport, wave propagation• Chemical reactions including SO2, Cl, etc.
• Comparison with telescope observation

qCoupling with a lower atmosphere VGCM
• Interaction with lower atmosphere• Effects of radiative reactive cloud

Better understanding of general circulation
and atmospheric chemistry2021/03/11[Bierson and Zhang., 2020]25