A Global Observation of S4 Scintillation Index
Ob
Observed
d bby M
Means off
FORMOSAT 3/COSMIC
1 2 [email protected]
Tiger J.Y.
Ti
J Y Li
Liu1,
j li @j i
d
G. Uma1, P. S. Brahmanandam1, Koichi C.H. Chen3,
YK
Y.
Kakinami
ki
i1, C.
C H
H. Li
Liu4
1Institute
of Space Science,
Science National Central University,
University Chung-Li,
Chung Li Taiwan
2High Altitude Observatory, National Center for Atmospheric Research,
Boulder, Colorado, USA [email protected]
3Department
D
t
t off Geophysics,
G h i Graduate
G d t School
S h l off Science,
S i
Kyoto
K t University,
U i
it
Kyoto, Japan
4Academia Sinica, Taipei, Taiwan
Content
•
•
•
•
•
•
•
Introduction
Diurnal Variation
S
Seasonal
lV
Variation
i ti
Geomagnetic Activity Variation
S4 vs. the F2-peak
E-region
E
region S4 Scintillation
Conclusion
Introduction
Worst case fading depth for solar maximum
and minimum at L-band (Basu et al., 1988).
F3/C S4 Index
The F3/C S4 index is computed
p
from the raw 50-Hz
L1 (1575.42 MHz) amplitude measurements which is
ggiven as follows:
S 
4
(I  I )
I
2
Analysis
• Seasonal Variation: four seasons - M-months
(March 21 ± 1.5 month), J-months (June 21 ± 1.5
month), S-months (September 21 ± 1.5 month), Dmonths (December 21 ± 1.5
1 5 month)
month).
• Geomagnetic Activity Variation: quiet (Kp: 0-3) &
di t b d conditions
disturbed
diti
(K
(Kp: 3+-9).
9)
Diurnal Variation
Seasonal Variation
The equatorial F-region scintillations occur during 1900-0300 MLT.
The latitudinal distribution is often beyond ±15o magnetic latitudes.
The S4 index gradually expends towards from the equator to the northern hemisphere
at 150 to 350 km altitude.
The F-region
F region scintillation in the equator and low latitudes similar to M-months
M months but
more intense.
The nighttime scintillation activity in equatorial and low latitude F-region becomes the
most intense during D-months.
The scintillation activity at lower altitudes appears throughout the day with the highest
value at around 1200 MLT.
Comparing the other months,
months the S4 index in the E-region is very pronounced in
the northern hemisphere, and however, the equatorial and low-latitude F-region
scintillation becomes very weak.
S4 vs. the equatorial F2 peak
The intense scintillations in the equatorial ionosphere generally occur below
the F2-peak. The S4 index maximum time appears at 2300, 0100, 2200, and
2300MLT in the M, J, S, and D-months respectively.
Geomagnetic and Geographical Variation
The S4 Index of the E-region
(75-125km altitude)
The maximum S4 index lies between ~250 and 500 geographic latitudes.
Monthlyy variation of the E-region
g
S4
Conclusion (I)
• It is interesting to find the S4 scintillation
g
in the mesosphere.
p
signatures
• The most pronounced S4 scintillation occurs in
the ionospheric E-region
E region, which becomes
remarkable in low latitudes of the summer
hemisphere.
hemisphere
• The S4 index of the low-/mid-latitude
ionospheric F
F-regions
regions starts developing in the
post sunset period, become pronounced in the
pre midnight and diminishes around the pre
pre-midnight,
predawn.
Conclusion (II)
• Results show that the S4 scintillation is generally
p
(p
(physical
y
mechanism?))
below the F2-peak
• The E-region S4 index yields clear seasonal and
geographical signatures
signatures.
• The S4 scintillation is more pronounced during
geomagnetic quite
quite.
• The FORMOSAT-3/COSMIC for the first time
provides
id 3
3-D
D observations
b
ti
off th
the S4 scintillation.
i till ti
• It is found that the S4 scintillation in the polar
region is NOT pronounced as previous models
predicted.