Coordinated ground-based measurements and modeling of
the Venus atmosphere (28-29 June 2010, Paris observatory)
Propagation on waves and wave-wave interaction
in the Venus upper atmosphere
Naoya Hoshino1, H. Fujiwara1, M. Takagi2,
Y. Kasaba1, Y. Takahashi3
1. Tohoku Univ., 2. Univ. of Tokyo,
3. Hokkaido Univ.
1. Introduction
金星大気構造
Structure of Venus atmosphere
thermosphere
mesosphere
Temperature
Day: ~300 K
Night: ~100 K
-> SS-AS conv.
Wind field is unknown
cloud
troposhpere
Superrotation
(~100m/s)
Fig. 金星大気構造
2
1. Introduction
金星大気構造
金星大気構造
1) Fast mean zonal flow
熱圏
(35 m/s [Lellouch et al., 1994])
Waves
~132 m/s[Shah et al., 1991])
中間圏
2) Temporal variations
雲層
対流圏
Fig. 金星大気構造
Fig. NO airglow (115 km)
[Bougher et al., 1994]
3
1. Introduction
Previous studies
波長
金星一周
100 km
Rossby waves
(5 days)
Thermal tides
(117 days)
The gravity
waves have
been taken into
account.
50
Kelvin waves
(4 days)
Gravity waves
100
位相速度 (m/s)
Vertical momentum transport associated with
the gravity waves generates fast mean zonal
flow of ~60 m/s in the thermosphere.
(However, we are quite uncertain how much
momentum is transported by the gravity
waves from below.)
4
Fig. 金星熱圏風速場のシミュレーション結果 [Zhang et al., 1996]
1. Introduction
Subjects
・Taking into account planetary waves (Kelvin wave, Rossby wave,
and thermal tides), their vertical propagation and effects on
atmospheric circulation in the mesosphere and thermosphere in
the Venus atmosphere.
• Which wave is predominant?
• What kind of waves are generated by wave-wave interaction?
5
2. Model
GCM
N step
Temperature
Velocity (u, v, w)
Number density
(O, CO, CO2)
Eddy viscosity
Molecular diffusion
EUV heating
NIR heating
CO2-15um cooling
GCM
•Primiive equations
•80-180 km
•10°(lat)×5°(lon)×0.5 SH
O, CO2
Airglow model
N+1 step
Temp.
Velocity (u, v, w)
Number dens.
(O, CO, CO2)
Fig. GCMと大気光モデルとの関係
Horizontal
distribution of
airglow is
diagnosed.
2. Model
Excitation of wave
Waves are excited by
geopotential forcing given
at the bottom (80 km).
Amplitude:
Velocity of wave horizontal
winds is 10 m/s (Rossow et
al., 1990)
Excited waves
Fig: Geopotential forcing
Phase velocity:
Thermal tide: 3 m/s (117 day)
Rossby wave: - 85 m/s (5 day)
Kelvin wave: -115 m/s (4 day)
Example of the geopotential forcing
(Kelvin wave)
7
3. Result
Predominant wave
Waves excited at 80 km
propagates to ~130 km.
Maximam velocity of
horizontal wind
associated with wave is
~9 m/s at ~95 km.
8
Zonal wind associated with the wave on the equator.
3. Result
propagating eastward
~3.7 m/s (120 day)
Generated by interaction
between Kelvin wave and
EUV heating.
Kelvin wave
Kelvin wave is
predominant in the
mesosphere.
propagating westward
~110 m/s(4.0 day)
Time variation of zonal wind deviation on the equator
at ~95 km.
3. Result
Fourier analysis
A wave whose period is
~2.4 day is detected.
Kelvin wave (forced)
->This wave may be
generated by the interaction
between the Kelvin (~4
days) and Rossby (~5 days)
waves.
Kelvin wave
Period: 4 days
Wavenumber: 1
Rossby wave
Period: 5 days
Wavenumber: 1
Black: 95 km
Red: 120 km
Wave1
Period: 2.2 days
Wavenumber: 2
Wave 2
Period: 20 days
Wavenumber: 0
Rossby wave (forced)
3. Nightglow model
Time variation of airglow distribution
1.2日
4.5日
9.0日
緯度(deg)
90
-90
With waves
Without waves
12
06
00
Local Time
(hour)
18
Fig. 12. 大気光発光位置の時間変動
•Airglow distribution varies temporally with a period of ~3.3-4.5 days.
•Zonal shift is 00:00LT – 00:40LT.
12
4. Summary
Numerical experiments in which the planetary waves (Kelvin
wave, Rossby wave, and thermal tides) imply that
• the Kelvin wave is predominant in the Venus mesosphere.
• the Kelvin wave propagate upward to ~120 km.
• the amplitude of the Kelvin wave is modulated by the EUV
heating (period is ~120 Earth days).
• Nonlinear interaction between the Kelvin and Rossby waves
may produce a wave whose period is ~2.4 days.
• the airglow distribution temporally varies (~3-4 days
period); the zonal shift due to the waves is 00:00LT-00:40LT.
Concluding remarks
• Any kind of observation is useful for the mesospheric and
thermospheric modeling because the models are rather
conceptual at present.
• I like to know…
– Time variation of mean zonal flow, SS-AS circulation, and other
components (if any). First of all, we must to know details of
what to be modeled.
– Quantitative information of the waves at the cloud level (spatial
structure, phase speed, amplitude), which is fundamental to the
wave-drag parameterization.
• Simultaneous observations of the airglow and horizontal
wind distributions seem quite informative for the modeling.
• Vertical temperature profiles with wide localtime coverage
are also useful to examine the thermal tides.
5. Future work
今後
・重力波効果の考慮
→ Medvedev et al. [2000] のパラメタリゼーション
Fig. 東西風の赤道面分布
Fig. 経度方向に平均した東西風の分布
3. Result
その他の波
ケルビン波
約2.4日周期 にピーク
->ケルビン波(4日周期)と
ロスビー波(5日周期)との
相互作用?
130km
110km
ケルビン波
周期: 4日
波数: 1
Wave1
周期: 2.2 日
波数: 2
95 km
ロスビー波
ロスビー波
周期: 5日
端数: 1
Wave 2
周期: 20 日
波数: 0
Fig. 10. 各高度で値を規格化した東西風時間
変動のパワースペクトル
3. Result
卓越する波
大気波動は約120 km
まで伝搬
波による風速擾乱の最
大値9m/s (@約95 km)
16
Fig. 東西風擾乱の赤道面分布(正が東向き風、負が西向き風)
3. Result
大気光の水平面分布(波なし)
Latitude (deg)
90
0
-90
12h
6h
0
2
0h
Local Time
4
18h
6
Fig. 11. 大気光水平面分布
8
12h
10
・最大発光強度約 9 MR → 先行研究に比べ (2-3倍大きい)
・反太陽直下点で発光量最大
3. Result
波動-波動相互作用
X  cos( s1   1t )  cos( s2    2t )
波1
波2
1
cos(2s1  2 1t )  cos(2s2  2 2t )
2
 cos( s1  s2 )  ( 1   2 )t 
X 2  1
 cos( s1  s2 )  ( 1   2 )t 
波動-波動により生じる
新たな波
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金星大気構造 - LESIA