Structure and dynamics of the ionization ledge observed from the topside sounder satellites

1
Structure and dynamics of the ionization ledge
observed from the topside sounder satellites

• IAGA 2005 Scientific Assembly
• Toulouse, France
• 18-29 July, 2005
• J. Uemoto(1), T. Ono (1), A. Kumamoto (1) and M.
  Iizama (1)
• Department of Geophysics, Graduate school of
  Science, Tohoku University, Japan

2
Table of Contents
1. Introduction, Purpose and topics
Early studies of the F3 layer and the ionization
ledge Purpose and problems to be solved Topics
4. Discussion
5. Conclusion
3
1. Introduction, Purpose and topics
Early studies of the F3 layer and the ionization
ledge Purpose and problems to be solved Topics
4
The F3 layer and the ionization ledge
1000LT
F3
Altitude km
F2
Plasma Density /cc
F3
Altitude km
F2
1400LT
Plasma Density /cc
Fig. 1. N(h) profile calculated from the SUPIM
model Balan et al., 1995.
5
Problems to be solved
Purpose
To clarify the relation between the F3 layer and
the ionization ledge and the mechanism of them
6
Topics
7
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8
Coverage of analyzed sounder data
30
30
20
20
10
10
0
0
-10
-10
-20
-20
-30
-30
-40
Ohzora
-50
Geographic Latitude deg.
Figs. 2. The coverage of the analyzed sounder
data.
Geographic Longitude deg.
9
A typical example of the ionization ledge
Frequency MHz
10.0
0.1
1.0
2.0
4.0
7.0
0.0
DATE 1975/09/22 UT 054749 LT
2.13 h Dip Lat. - 0.04 º Alt.
1379.11 km
4.4
Delay Time ms
8.8
13.3
Cusp
ledge peak
17.8
Maximum error Ohzora satellite 27 km ISIS-2
satellite 68 km
1400
Enhance rate
1000
Altitude km
ledge peak
600
Cusp
Figs. 3. The ionogram showing the existence of
the ionization ledge (Upper panel) and the
reduced N(h) profile (Lower panel).
200
104
105
106
Plasma Density /cc
10
The definition of the ledge altitude
1400
DATE 1973/03/20 LT 0.04 h
1200
1000
? ledge peak
800
Altitude km
cusp
600
Ledge field line
400
200
-30
-20
-10
0
10
20
30
Dip latitude deg.
Fig. 4. Contour plots of the plasma density
observed from the ISIS-2 satellite on 20 March,
1973 at mid night local time sector.
We adopted the altitude of the ledge field line
over the dip equator as the ledge altitude.
The ledge peaks existed along a same field line
11
The relation between ledge altitude and local time
? Ohzora
? ISIS-2
1200
1000
Altitude 490 1266 km
Ledge altitude km
Local time 9.02.6 hr
800
600
400
6
10
15
20
1
6
Local time hr.
Fig. 5. Local time variation of the altitude of
ledge field line over the dip equator.
The ionization ledge was observed at all local
time sector except for 03 08 LT
These data were scattered and the ledge altitude
seems to be independent on the local time.
12
Seasonal dependence of the occurrence
75.0
80
Ohzora
60
36.5
40
No Data
No Data
20
0
30
Occurrence probability
ISIS-2
21.1
17.5
20
11.3
7.5
10
0
2-4
5-7
8-10
11-1
(Spring)
(Summer)
(Autumn)
(Winter)
Month (Season)
Fig. 6. Seasonal dependence of the occurrence
probability of the ionization ledge obtained from
the Ohzora (upper panel) and the ISIS-2
satellites data (lower panel).
The occurrence probability tends to be higher in
equinox season and lower in solstice season
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Summary of topside sounder data analysis
The ionization ledge was observed
-13.5 19.3
Dip latitude range
Local time sector
All local time sector except for 03 08 LT
Altitude range
490 1266 km
The altitude of the ledge structure seems to be
independent on the local time.
Local time dependence
Higher in equinox season Lower in solstice season
Seasonal dependence
14
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15
Estimation of Electric field variation in the
equatorial ionosphere
16
Comparison Electric field and occurrence
328.3
Ledge occurred
Not occurred
262.6
March and May, 1987
197.0
131.3
Plasma Upward displacement ?h km
65.7
0
71
79
125
138
75
83
127
145
72
77
82
124
126
132
142
146
day
Fig. 9. Relationship between the occurrence and
the time integrated E field.
Ionization ledge is associated with the electric
field enhance
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Discussion -Local time dependence of ledge
altitude
Ionization ledge is caused by F2 plasma upward
motion due to daytime electric field
60
40
Enhancement
20
0
Fig. 11. The relation between the altitude and
the enhancement at the ledge peak.
600
400
800
1000
1200
Altitude of ledge km
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Discussion -Seasonal dependence of the occurrence
Seasonal dependence of occurrence probability
Higher in equinox season Lower in solstice season
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Conclusion
To clarify occurrence character of the
ionization ledge and To clarify the relation
between the ionization ledge and the ionospheric
electric field, we analyzed the sounder data
obtained from the Ohzora and the ISIS-2
satellites and the geomagnetism data.
-13.5 º 19.3 º
Dip latitude range
Local time range
All local time except for 3 8 LT
Altitude range
490 1266 km
The occurrence of the ionization ledge is
associated with the electric field enhance.
The occurrence probability of the ionization
ledge tends to be higher in equinox season and
lower in solstice season. It is suggested that
the seasonal variation of the electric field
controls that of the occurrence probability of
the ionization ledge.
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Acknowledgement
Thank you very much for your kind attention!
We are grateful to NSSDC and the ISIS / Alouette
Topside Sounder Data Restoration Project team for
providing the Allouette and ISIS satellites
sounder data.
We are also grateful to World Data Center for
Geomagnetism, Kyoto for providing the
geomagnetism data.
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1973-79
30
30
20
20
10
10
0
0
-10
-10
-20
-20
-30
-30
-40
ISIS-2
-50
24
ltLocal time dependence of occurrence probabilitygt
60
40
Occurrence probability
20
0
10
6
15
20
25
29
Local time hr
Fig. The local time dependence of the occurrence
probability of the ionization ledge.
25
ltLocal time dependence of the ledge altitudegt
1200
1000
800
600
? Ohzora
? ISIS-2
400
6
10
15
20
25
30
Altitude of ledge field lines apex km
Local time hr
Lockwood and Nelms, 1964
800
Oct., Nov., and Dec., of 1962
600
400
12
8
16
20
24
Local time hr
Fig. The local time dependence of the ledge field
line altitude.
26
ltRelation between ledge and electric fieldgt
Jicamarca Radio Observatory Incoherent Scatter
Data Base
Weighted average over height interval 235 to 570
km
Fig. 23. The observed vertical drift _at_ Jicamarca
on Sep. 16, 1999.
Vertical drift m/s
Fig. 24. The calculated vertical drift on Sep.
16, 1999 at 400 km.
27
ltSolar activity gt
ISIS2
Ohzora
Fig. Solar activity. http//sidc.oma.be/html/sidc
_graphics.html
28
ltEstimated Error Magnitudegt
???????????????????
N(h)??????????????
Ray-Path Tracing??? ???????????
1400
1600
(-10.78, 703.39)
2.5 MHz
1400
1200
1000
40 km
1000
800
Altitude km
Altitude km
600
?
600
13 km
400
(-10.13, 716.50)
200
200
104
106
105
-9.0
-10.0
-11.0
-12.0
Plasma Density /cc
Geographic Latitude deg.
Fig 10. A typical example of error estimation.
Fig 11. A typical example of error estimation.
27 km for Ohzora, 68 km for ISIS-2.
29
ltEquatorial Electro-Jet (EEJ)gt
Equatorial Electro-Jet (EEJ)
?????????Sq????????????????????????????????
??????????????????Conductivity???????
Fig. Sq (Solar Quiet) current system.
Jpz
Fig. Concept of generation of cowling
conductivity.
30
lt TEL system was contaminated from Sounder pulse?gt
?????????????????????????
5.0
Sounder????
4.0
TeK
3.0
x103
NPW ????
2.0
1.0
10.6
10.7
10.8
10.9
Local TIMEHOUR
Fig. A typical example of TEL observation.
????????Sounder????????????
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ltElectron Temperature in the ledge structuregt
Electron temp. x103K
1.6
6.4
11.2
MHz
0
Dip latitude deg.
2
Fig. The variation of the electron
temperature.
4
Delay Time ms
6
ledge???????????????????????????????????
7.3
Fig. The ionogram observed through the passage of
the satellite in the ionization ledge structure.
32
ltSeasonal dependence of occurrence probabilitygt
Balan et al., 1998
Occurrence probability
Month
Fig. The Seasonal dependence of occurrence
probability.