HR: 1340h
AN: SA33B-1327    [Abstracts]
TI: Occurrence characteristics of plasma bubble derived from global ground-based GPS receiver networks
AU: * Nishioka, M
EM: nishioka@kugi.kyoto-u.ac.jp
AF: Department of Geophysics, Graduate School of Sciece, Kyoto University, 4th building, Scinece Dept, Kyoto Univ, Oiwake-cyo, Sakyo-ku, Kyoto, 606-8224, Japan
AU: Saito, A
EM: saitoua@kugi.kyoto-u.ac.jp
AF: Department of Geophysics, Graduate School of Sciece, Kyoto University, 4th building, Scinece Dept, Kyoto Univ, Oiwake-cyo, Sakyo-ku, Kyoto, 606-8224, Japan
AU: Tsugawa, T
EM: tsugawa@stelab.nagoya-u.ac.jp
AF: Solar-Terrestial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
AB: Occurrence characteristic of plasma bubble was studied with ground-based GPS receiver networks. The coverage of the observation with global grond-based GPS receivers is wider than that with the other observatinal instruments because of the large number of receivers. The physical characteristics of plasma bubble occurrence were studied in detail with this novel data set. 23 GPS receivers around the dip equator were used to reveal occurrence of plasma bubble from 2000 to 2006. Monthly and semiannual occurrence rates for all longitudinal regions were studied. Characteristics of the monthly occurrence rates were different among the regions. Although it was found that sunset time lag effect plays an important role for the monthly variation, two asymmetries which could not be explained with the sunset time lag scenario were found: (1) asymmetry between two solstices and (2) asymmetry between two equinoxes. (1) was found in all of the regions. The F-region conductivity integrated along the geomagnetic field line, Σ_F^P, could affect on this solstice asymmetry. (2) was found in every region. (2) in the Central Pacific region was found for seven years from 2000 to 2006. Semiannual occurrence rates from 2000 to 2006 were used to study the year-to-year variation from the high solar activity period to the low solar activity period. The dependency of plasma bubble occurrence on the solar activity was different among the regions. In the Asian region, the occurrence rates decreased from 70% in 2002 to 10% in 2006. In the Atlantic region, on the other hand, the occurrence rates were between 20% and 50%, and did not show linear decrease as the solar activity. Occurrence rates against the latitude/altitude were also investigated in the Asian region in 2004. It was found that the occurrence was high and constant below 700km altitude on the dip equator. They began to decrease when the the altitude was higher than 700km, and was almost zero where the HODE was higher than 900km.
DE: 2400 IONOSPHERE (6929)
DE: 2415 Equatorial ionosphere
DE: 2439 Ionospheric irregularities
SC: SPA-Aeronomy [SA]
MN: 2007 Fall Meeting