Global Distribution of E quatorial P lasma B lobs in the Pre-midnight Sector

1. Global Distribution of Equatorial Plasma Blobs in the Pre-midnight Sector 3 May. 2005 Jaeheung PARK

2. Part 1. Review

3. Equatorial Plasma Bubble : sharp decrease of plasma density in equatorial region

4. Rayleigh-Taylor instability • When heavy fluid sits above lighter fluid in a gravitational field • Bubbles of light fluid rise into the heavier medium

5. General Features of EPB micro-structure  wave scattering • Scale lengths : several meters ~ several hundred kilometers • Local time : sunset to sunrise • Field-aligned structure • Forming a vertical channel • Adverse effects on the radio communication • Seasonal-longitudinal distribution

6. Plasma blobs? • plasma density enhancement in narrow region : a rare phenomenon • Few precedent studies KOMPSAT-1

7. History • Hinotori observation (Japan) – Watanabe and Oya (1986) discovery of the phenomenon • ROCSAT-1 observation (ROC) – Le et al. (2003) • KOMPSAT-1 observation (Korea) - Park et al. (2003)

8. General Features of Blobs • peak density : several times that of the ambient. • upward drift • spectral behavior similar to that of EPBs

9. Electron temperature : lower than that of the ambient

10. Chemical composition : oxygen-rich

11. along the ±15o magnetic latitudes • S/L distribution : nearly identical to that of the EPBs

12. Other characteristics • correlation of the blob occurrence with the solar F10.7 index : -0.47 • KOMPSAT-1 made 129 equatorial crossings for the geomagnetic activity Kp higher than 4.3, but no plasma blobs were observed on these orbits. • Non-adiabatic expansion during the uplift • Stable structure over 1.5 hours

13. Suggested Theories EPB enhanced eastward E-field  • Direct mapping along the geomagnetic field (Le et al., 2003) • Enhanced fountain effect (Park et al., 2003)

14. Part 2. Progress

15. Contradictory Evidences • Dependence on yearly-averaged solar activity • Seasonal-longitudinaldistribution

16. bubble

17. blob

18. Depletion depth of bubbles • Strength of the eastward E-field • Efficiency of the fountain motion

19. March equinox Bubble Blob

20. September equinox Bubble Blob

21. June solstice Bubble Blob

22. December solstice Bubble Blob

23. Conclusions - 1 • along ±15o magnetic latitudes • No correlation with the daily variation of solar activity • S/L distribution : similar to that of the EPBs • drift, electron temperature, and H+ proportion : similar to those of the EPBs. • Therefore, it is suggested that the blobs originated from the lower altitudes by a mechanism that drives an upward drift of EPBs.

24. Conclusions - 2 • Dependence on yearly-averaged solar activity : NO! • Seasonal-longitudinal distribution : significant departure from that of bubbles : except during December solstice • Terminator-field alignment? : only in solstices • Equinoctial blobs  ambient density level (x) vertical drift speed (x)

25. evening prereversal enhancement (EPE) • vertical drift speed • F-region dynamo ; Fejer et al. [1999]