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Ann. Geophys., 24, 2991-2996, 2006
www.ann-geophys.net/24/2991/2006/
© European Geosciences Union 2006
Ionospheric height variations observed by ionosondes along magnetic meridian and plasma bubble onsets
S. Saito and T. Maruyama
National Institute of Information and Communications Technology, Nukui-kita 4-2-1, Koganei, Tokyo 183-8795, Japan
Abstract. Since October 2004, a Frequency Modulated–Continuous Wave (FM–CW)
ionosonde chain along the magnetic meridian
has been operating in Southeast Asia, in
Kototabang (0.2° S, 100.3° E), Indonesia,
Chumphon (10.7° N, 99.4° E), Thailand, and
Chiang Mai (18.8° N, 98.9° E), Thailand.
Variations in the virtual height of the bottomside of the F-region (h'F)
at 2.5 MHz were
analyzed, in order to study the day-to-day variability of plasma bubble occurrence
for the periods of October 2004 and March–April 2005.
When plasma bubbles were generated,
h'F was enhanced at the three stations.
However, even when h'F at the equatorial station,
Chumphon, was largely enhanced,
plasma bubbles were not generated
when a noticeable north-south asymmetry of h'F existed.
This asymmetry could be attributed
to the transequatorial thermospheric wind. Our results show that the strong
transequatorial thermospheric wind can suppress the plasma bubble generation
and is one of the important factors which controls the day-to-day variability
of plasma bubble occurrences.
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