SEALION F3

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SEALION ??????????????F3 ???????
????(1) ????(1), ???(2), ???(2),????(1), ????(1)
(1)???????? (2)NICT
2006? ???????? (MTI) ????
2006.09.25, 26 ???????
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Equatorial Ionosphere
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The equatorial ionosphere has been extensively
studied by observational and theoretical methods
since the initial ground-based observations of
the equatorial anomaly.
Log 10(Raw pixel cnts)
Fig. EA observed by FUV/IMAGE 2002/04/24
184227UT. NSSDC
Geographic Latitude deg
Fig. Plasma dynamics in the equatorial region
(Geographic longitude is about 99 deg)
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Additional layer above the F2 peak
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The existence of an additional layer has been
known.
From the ground
From the space
Ratcliffe (1951)
Sayers et al. (1963)
Macnish (1950) reffered in his paper
Langmuir probe
Ionosonde
Lockwood and Nelms (1964)
Topside sounder
Equivalent Height
Huancayo
Frequency
Fig. An ionogram showing the ledge recorded at 72
º W, 11 º S at 0039 GMT on 2 Oct., 1962.
Fig. Sketches of successive h-f curves.
F3 layer
Ionization ledge
Same phenomenon?
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SUPIM model calculations
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Studies for the F3 layer have been extensively
advanced since Balan and Bailey 1995 has
reproduced the F3 layer using the SUPIM model.
Figs. Calculated N(h) profiles without F3 layer
(left panel) and with F3 layer (right panel)
using SUPIM model Balan et al., 2000.
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Proposed physical mechanism of the F3 layer
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Neutral Wind
1000
0400LT 1000LT 1400LT 2000LT 2400LT
Summer
Winter
800
600
Altitude km
400
200
105
106
107
10
20
-10
-20
0
Plasma density /cc
Magnetic latitude ?
Vz
Vertical Ion velocity
Figs. N(h) profiles (left panel) Balan and
Bailey, 1995 and vector plasma flux at 12 LT
calculated by SUPIM model Balan et al., 1998.
U
Meridional neutral wind
I
E x B drift
Inclination
VExB
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Observations of the F3 layer
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The existence of the F3 layer has been confirmed
in Brazil(Balan et al., 1997 etc.), India(Rama
Rao et al., 2005), and South east Asia(Hsiao et
al., 2001 etc.).
Figs. Seasonal dependences of occurrences based
on the ionogram data observed at at Waltair in
1997 Rama Rao et al., 2005 (top panel) and
Fortaleza in 1995 Balan et al., 1998 (bottom
panel) .
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Open questions
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Reported tendency of occurrence probabilities of
the F3 layer at Fortaleza in Brazil is different
from SUPIM model prediction.

Tendency of occurrences at Waltair in India is
different from that at Fortaleza in Brazil.

Geographic control?
Dip latitudinal effects?
The situation of the F3 layer in the whole low
dip latitude region has not been observed.
Simultaneous magnetic conjugate observations are
needed!
Fig. Frequency of occurrence of the F3 layer over
Fortaleza and the variation with magnetic dip
angle of Fortaleza during the two and a half most
recent solar cycles, represented by the F10.7
index Batista et al., 2002.
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Purpose of this study
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Clarifying the mechanism of the F3 layer in more
detail through analyzing ionosonde data observed
from the Southeast Asia Low-latitude Ionospheric
Network SEALION.
Contribution
Understanding basic problems of the interaction
between thermospheric neutral atmosphere and
ionospheric plasma since the F3 layer is one of
the representative phenomena caused by this
interaction.

Perhaps deducing the daytime meridional neutral
wind which it is difficult to observe.

In this presentation, I will show you observation
results which indicate dip latitudinal
dependences of the F3 layer and suggest an
explanation for dip latitudinal dependences.
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What is the SEALION ?
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Southeast Asia Low-latitude Ionospheric Network
Focusing on studying and predicting ionospheric
scintillations
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Analysis period and ionogram examples
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KTB
Station Code
CPN
CMU
04
07
10
01
04
07
10
01
04
07
10
01
2003
2004
2005
Date Month
Fig. Observation periods at 3 stations
Figs. Examples of ionogram without (left panel)
and with F3 layer (right panel).
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Dip latitudinal variations on 31 March, 2005
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500
400
300
200
Characteristics and dynamics of the F3 layer at
low latitude region are different from those in
the vicinity of the dip equator.
700
600
500
Virtual Height km
400
300
200
500
400
300
200
31st Mar., 2005
0700
1900
Local Time hrs
Figs. Sequence plots of O-mode echo traces
appeared on ionograms on 31 March, 2005.
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Dip latitudinal variations on16 November, 2004.
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500
400
300
200
The F3 layer was not observed at CPN!
700
600
500
Virtual Height km
400
300
200
600
500
400
300
200
16th Nov., 2004
0700
1900
Local Time hrs
Figs. Sequence plots of O-mode echo traces
appeared on ionograms on16 Nov., 2004.
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Occurrence probabilities of F3 layer
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Fig. Occurrence probabilities of the F3 layer at
CMU, CPN and KTB.
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Observation Results
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31 Mar., 2005.
At CPN, the F3 layer moved upward rapidly and
disappeared in earlier LT.
At CMU and KTB, the F3 layer almost stayed at a
certain altitude and was observed with longer
time duration.
16 Nov., 2004.
At CPN, the F3 layer was not observed.
At CMU, the F3 layer moved upward gradually until
1215LT, and moved downward gradually.
At KTB, the F3 layer moved upward gradually until
1015LT.
Occurrence probabilities
Lowest probability in Dec. solstice season at
CMU,CPN and KTB.
It can be explained by seasonal dependences of
the E x B drift.
Tendencies of occurrence at CPN differed from
those at CMU and KTB.
Tendency of occurrence prob. at CMU and KTB were
very similar.
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Can proposed mechanism explain obs. results?
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The answer is
No!
Diffusion
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Possibly new mechanism -1
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In the vicinity of the dip equator
The E x B drift moves plasma upward more
efficiently.
Plasma at the upward drifted F2 peak diffuses to
higher altitude and becomes thinner soon than
that at the usual F2 peak.
Moving upward rapidly
Shorter duration time
In the low dip latitude region
The E x B drift moves plasma upward less
efficiently.
Plasma is transported to the upward drifted F2
peak altitude and plasma density can be sustained
higher than that at the usual F2 peak.
Staying at almost same altitude
Longer duration time
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Possibly new mechanism -2
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Higher density peak
?
Lower density peak
?
E x B drift
Altitude
Field aligned diffusion
F2 layer
1
K
P
M
Dip Latitude
Figs. Pictures of time development of the
additional layer based on the new mechanism.
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Possibly new mechanism -3
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Preventing field aligned diffusion to higher
altitude is important for observations with
longer time duration in the vicinity of the dip
equator.
In the vicinity of the dip equator
In the local summer season when neutral wind
prevents diffusion.
In the low dip latitude region
In the season when the E x B drift becomes
stronger.
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80
60
Occurrence
40
20
0
01
03
05
07
09
11
Month
Fig. Occurrence probabilities of the F3 layer at
CMU, CPN and KTB.
Fig. Seasonal dependence of the vertical ion
drift velocity Scherliess and Fejer, 1999.
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Applying for the ionization ledge
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Based on this mechanism, the ionization ledge
should be formed
inside the region between the equatorial anomaly
crests.
aligned the magnetic field line crossing the
crests.
slightly later local time after the F3 layer is
formed.
Fig. Contour plots of the plasma density on March
20, 1973 Uemoto et al., 2006.
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Reported occurrence probabilities in Brazil
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80
40
Geographic Latitude ?
00
?
Fortaleza
-40
-80
-100
0
100
Geographic Longitude ?
Fig. Locations of Fortaleza and Waltair.
It is inferred that neutral wind which moves
plasma along magnetic field lines in Brazil is
peculiar and should be studied in more detail.
Figs. Seasonal dependences of occurrences of the
F3 layer found from the ionogram data observed at
Fortaleza Balan et al., 1998 and those of the
ionization Uemoto et al., 2006.
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Conclusion -1
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For clarifying the F3 layer in more detail, we
are analyzing ionosonde data observed from the
SEALION ionosonde network.
From simultaneous conjugate observations, dip
latitudinal variations of the F3 layer has been
clearly confirmed for the first time.

From statistical analysis of occurrence
probability of the F3 layer, the F3 layer occurs
less frequently in December solstice seasons at 3
stations and tendency of occurrences in the
vicinity of the dip equator is different from
that in the low dip latitude region.

It is suggested that dip latitudinal variations
and seasonal dependences of occurrence
probabilities found in present analyses can be
explained, if the magnetic field line crossing at
the upward drifted peak in the vicinity of the
dip equator also crosses that in the low dip
latitude region and adding the field aligned
diffusion effects to the mechanism proposed by
Balan et al. (1998).

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Conclusion -2
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This mechanism is consistent with reported
characteristics of the ionization ledge. Then,
based on this mechanism, the F3 layer and the
ionization ledge can be interpreted as a sequence
of phenomenon which is peculiar in the equatorial
ionosphere and it is implied that decreasing
field aligned diffusion speed caused by the
neutral anomaly might be not necessary needed to
form the ionization ledge structure.

Future works
To prove validity of this mechanism,,,
Model calculation with the SAMI2 model provided
by NRL Huba et al., 2000.
Comparing present analysis results with the data
obtained from the CHAMP satellite.
From the CHAMP satellite data, position of the
enhanced plasma density flux tube might be
detected.
Analyzing geomagnetic data for deducing daytime
zonal electric field.
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Acknowledgements
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The SAMI2 model
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Log10 density /cc
Altitude km
Geographic Latitude deg
Fig. Contour plot of plasma density calculated
from SAMI2 on 31st March, 2005 UT 030630 with
doubled E x B drift and no neutral wind (or
normal wind?).
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Log10 density /cc
Altitude km
?
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?
?
?
?
Geographic Latitude deg
Fig. Contour plot of plasma density calculated
from SAMI2 on 31st March, 2005 UT 030630 with
doubled E x B drift and no neutral wind (or
normal wind?).
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Log10 density /cc
Altitude km
?
?
?
?
?
?
Geographic Latitude deg
Fig. Contour plot of plasma density calculated
from SAMI2 on 31st March, 2005 UT 030630 with
doubled E x B drift and no neutral wind (or
normal wind?).
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Fig. N(h) profiles calculated from SAMI2 on 31st
March, 2005 UT 030630 with doubled E x B drift
and no neutral wind (or normal wind?) at each
adjusted station.
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Difference of field lines between SAMI2 and IGRF
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Result A
A1
Altitude km
Altitude km
Geographic Latitude deg
Geographic Latitude deg
Fig. Contour plot of plasma density calculated
from SAMI2 on 31st March, 2005 with 1.5
multiplied E x B drift and normal wind.
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Result A
A2
Altitude km
Altitude km
Geographic Latitude deg
Geographic Latitude deg
Fig. Contour plot of plasma density calculated
from SAMI2 on 31st March, 2005 with 1.5
multiplied E x B drift and normal wind.
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Result A
A3
Altitude km
Altitude km
Geographic Latitude deg
Geographic Latitude deg
Fig. Contour plot of plasma density calculated
from SAMI2 on 31st March, 2005 with 1.5
multiplied E x B drift and normal wind.
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Result A
A4
Altitude km
Altitude km
Geographic Latitude deg
Geographic Latitude deg
Fig. Contour plot of plasma density calculated
from SAMI2 on 31st March, 2005 with 1.5
multiplied E x B drift and normal wind.
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Result A
A5
Altitude km
Altitude km
Geographic Latitude deg
Geographic Latitude deg
Fig. Contour plot of plasma density calculated
from SAMI2 on 31st March, 2005 with 1.5
multiplied E x B drift and normal wind.