A Global Observation of S4 Scintillation Index Ob d b M fObserved by Means of

FORMOSAT 3/COSMIC

Ti J Y Li 1 2 j li @j i dTiger J.Y. Liu1, 2 jyliu@jupiter.ss.ncu.edu.twG. Uma1, P. S. Brahmanandam1, Koichi C.H. Chen3,

Y K ki i1 C H Li 4Y. Kakinami1, C. H. Liu4

1Institute of Space Science National Central University Chung Li Taiwan1Institute of Space Science, National Central University, Chung-Li, Taiwan2High Altitude Observatory, National Center for Atmospheric Research,

Boulder, Colorado, USA jyliu@ucar.edu3D t t f G h i G d t S h l f S i K t U i it3Department of Geophysics, Graduate School of Science, Kyoto University,

Kyoto, Japan4Academia Sinica, Taipei, Taiwan

ContentContent

• IntroductionIntroduction• Diurnal Variation

S l V i ti• Seasonal Variation• Geomagnetic Activity Variation• S4 vs. the F2-peak• E-region S4 ScintillationE region S4 Scintillation• Conclusion

Introduction

Worst case fading depth for solar maximumWorst 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 from the raw 50-HzpL1 (1575.42 MHz) amplitude measurements which isgiven as follows:

II )(2

g

I

IIS

)(4

AnalysisAnalysis• 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), D-months (December 21 ± 1 5 month)months (December 21 ± 1.5 month).

• Geomagnetic Activity Variation: quiet (Kp: 0-3) & di t b d diti (K 3+ 9)disturbed conditions (Kp: 3+-9).

Diurnal VariationDiurnal Variation

Seasonal VariationSeasonal 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 hemisphereat 150 to 350 km altitude.

The F region scintillation in the equator and low latitudes similar to M months butThe F-region scintillation in the equator and low latitudes similar to M-months but more intense.

The nighttime scintillation activity in equatorial and low latitude F-region becomes themost intense during D-months.The scintillation activity at lower altitudes appears throughout the day with the highestvalue at around 1200 MLT.

Comparing the other months the S4 index in the E-region is very pronounced inComparing the other months, the S4 index in the E-region is very pronounced inthe northern hemisphere, and however, the equatorial and low-latitude F-regionscintillation becomes very weak.

S4 vs. the equatorial F2 peak

The intense scintillations in the equatorial ionosphere generally occur belowthe F2-peak. The S4 index maximum time appears at 2300, 0100, 2200, and2300MLT in the M, J, S, and D-months respectively.

Geomagnetic and Geographical Variation

The S4 Index of the E-regionThe S4 Index of the E-region

(75-125km altitude)

The maximum S4 index lies between ~250 and 500 geographic latitudes.

Monthly variation of the E-region S4y g

Conclusion (I)• It is interesting to find the S4 scintillation

signatures in the mesosphere.g p• The most pronounced S4 scintillation occurs in

the ionospheric E-region which becomesthe ionospheric E region, which becomes remarkable in low latitudes of the summer hemispherehemisphere.

• The S4 index of the low-/mid-latitude ionospheric F regions starts developing in theionospheric F-regions starts developing in the post sunset period, become pronounced in the pre midnight and diminishes around the prepre-midnight, and diminishes around the pre-dawn.

Conclusion (II)• Results show that the S4 scintillation is generally

below the F2-peak (physical mechanism?)p (p y )• The E-region S4 index yields clear seasonal and

geographical signaturesgeographical signatures.• The S4 scintillation is more pronounced during

geomagnetic quitegeomagnetic quite.• The FORMOSAT-3/COSMIC for the first time

id 3 D b ti f th S4 i till tiprovides 3-D observations of the S4 scintillation.• It is found that the S4 scintillation in the polar

region is NOT pronounced as previous models predicted.