open access

https://hdl.handle.net/2115/32763

Solar activity dependence of the electron density in the equatorial anomaly regions observed by CHAMP

英語

2007-11-21

American Geophysical Union

Journal of Geophysical Research. A, Space physics

112(A11)

A11311

We have investigated the solar activity dependence of the electron density at equatorial and low latitudes using six years of measurements between Aug. 1, 2000–Aug. 1, 2006 from the CHAMP satellite, and compared it with the International Reference Ionosphere model (IRI). The solar activity dependence observed by CHAMP at 400 km altitude exhibits significant variation with latitude, season and local time. First, the electron density in the crest regions of the Equatorial Ionization Anomaly (EIA) grows roughly linearly from solar minimum to solar maximum, with higher growth rate than that in the EIA trough region. Second, the solar activity dependence in the EIA crest regions varies strongly with season. The growth rate of the electron density with increasing solar activity around equinoxes is about 1.5 to 2 times of that near solstices. Third, the solar activity dependence of the EIA structure varies significantly with local time. In the noon sector, the crest to-trough ratio (CTR) obtained at 400 km altitude varies within only a small range between 1.14 and 1.43 from solar minimum to solar maximum. In the post-sunset local time sector, however, the CTR grows remarkably with solar activity level, reaching values of above 3.9 at solar maximum. These differences are attributed to the different solar activity dependence of the vertical plasma drift in corresponding local time sectors. The IRI model was found to reproduce well the equatorial electron density near 400 km in the noon sector at all solar activity levels. However, it significantly overestimates it in the post-sunset to pre-midnight sector at high solar activity levels. The major cause for this overestimation has been found to be the 30 IRI's inadequate representation of the F2 layer maximum height (hmF2) in this sector, while the IRI's lack of equatorial spread F seems to play only a very small role.

学術雑誌論文

Accepted Manuscript

An edited version of this paper was published by AGU. Published (2007) American Geophysical Union. To view the published open abstract, go to http://dx.doi.org and enter the DOI.

0148-0227