Space-Earth Environmental Research

1. Yuichi Otsuka
Institute for Space-Earth Environmental Research,
Nagoya Univ., Japan

2. All-sky airglow imagers
Indonesia
2002～

3. Altitude
[km]
95
250
557.7 nm
Gravity wave
630.0 nm
airglow

4. 630nm airglow O+ + O2 → O2
+ + O
O2
+ + e- → O* + O
O* → O + hn(630nm)
V630nm ∝ [O+ ][O2]

5. Sata, Japan Kototabang
E W
S
S

6. Time sequence Nov. 12, 2001

7. Plasma Bubble
Plasma bubble is
elongated along the
geomagnetic field.
airglow
intensity
plasma
density
∝

8. Nov. 12, 2001 00:44LT
630-nm airglow

9. Longitudinal cross-section

10. plasma
bubble
electric field
Kototabang Chumphon Chiang Mai
1. Goemagnetic Conjugate Observation

11. Plasma
Bubble
Neutral Wind
Ｅ
Kototabang Chumpon Chiang Mai
Neutral Wind and Equatorial Ａｎｏｍａｌｙ

12. Ionospheric observations
in Indonesia
geomagnetic
equator
Equatorial Atmosphere Radar (EAR)
Kototabang
[0.20oS, 100.32oE;
dip lat. 10.4oS]
31-MHz radar all-sky airglow
imager

13. Airglow Observations at Geomagnetic Conjugate Points
Chiang Mai
Kototabang
All-Sky Airglow
Imager
Fabry-Perot
Interferometer
B-field
installed
by NICT

14. Chiang Mai
Kototabang
Geomagnetic Conjugate
Observations of
Plasma Bubbles
E
N
E
N
630-nm airglow

15. Chiang Mai
Kototabang
Eastward
Northward
cloudy
Eastward
Northward
Thermospheric Neutral Winds
90 m/s
120 m/s

16. 120 m/s
Zonal drift velocity of F-region
FAI (plasma bubble) is consistent
with zonal component of the
thermospheric neutral wind over
Kototabang.
F-region FAI Observed
With EAR
Local Time
Longitude
South
East
plasma bubble motion ⇔ ExB drift
E-field is generated mainly by neutral wind over

17. 560 Yagi antenna、peak power: 100kW
Equatorial Atmosphere Radar (EAR)
(0.20oS, 100.32oE)

18. EAR
W
E

19. 22:３５LT
630nm and ionospheric irregularities
Irregularities occur within entire plasma bubble.

20. GPS Scintillation （Indonesia）
2003 2004 2005 2006 2007
J
F
M
A
M
J
J
A
S
O
N
D
19 0 619 0 6 19 0 6 19 0 6
19 0 6
Local Time (hours)
S4
GPS scintillation occurs between
sunset and midnight in equinox.
Occurrence rate decreases with
decrease of solar activity.

21. Mechanism Generating
Plasma bubble
• Rayleigh-Taylor Instability
• Pre-reversal Enhancement

22. ＋
＋
＋
J
＋
＋
＋
－
－
ｰ
＋
＋
＋
－
－
ｰ
E
Rayleigh –Taylor instability
B
down
East

23. ＋
＋
＋
J
＋
＋
＋
－
－
ｰ
＋
＋
＋
－
－
ｰ
E
B
down
East
stable unstable
Rayleigh –Taylor instability

24. Plasma Bubble
Magnetic
field
Magnetic
equator
Plasma bubble
Meridional cross-section
High density
Low density

25. growth rate ： g
Growth Rate of the Rayleigh-Taylor Instability
Eastward E is effective because
- contribute to eastward J.
- move the F-region plasma to higher altitude. At high altitude,
gxB current become effective.
E: eastward electric field
B: magnetic field
b: gravitational acceleration
nin : collision frequency
n: plasma density
z: altitude

26. Vertical Drift
（positive upward）
= Eastward Electric Field
At the evening terminator,
drift velocity upward → downward
electric field eastward → westward
(evening enhancement;
pre-reversal enhancement)

27. Mechanism Generating Evening Enhancement
[Farley et al., 1986]
U
Ez= -UxB
Hall J
Map to E-region
Electric
Field
Negative Charge
Map to F-region
Upward
ExB
→ bubble

28. GPS Scintillation （Indonesia）
2003 2004 2005 2006 2007
J
F
M
A
M
J
J
A
S
O
N
D
19 0 619 0 6 19 0 6 19 0 6
19 0 6
Local Time (hours)
S4
GPS scintillation occurs between
sunset and midnight in equinox.
Occurrence rate decreases with
decrease of solar activity.

29. Plasma bubble occurrence
(seasonal and longitudinal variations)
[Burke et al., 2004]

30. Plasma Bubble Occurrence
• Seasonal and longitudinal variation is well
understood and can be explained by the pre-reversal
enhancement.
• For the purpose of the space weather, we need to
know where and when plasma bubbles occur.
• Mechanism of the day-to-day variation is unknown.
There are 3 candidate:
1. Upward propagating GW
2. LSWS (Large-Scale Wave Structure)
3. Meridional Neutral Wind
(asymmetry of equatorial anomaly)
No conclusive evidence showing which mechanisms are most effective.