Observational characteristics of ionospheric magnetic VLF wave in the solar minimum year

Ionospheric VLF wave recorded by the Instrument Magnetometer Search-Coil (IMSC) onboard the DEMETER spacecraft during 2007, the solar minimum year, were investigated statistically. By excluding the influence of geomagnetic activity with geomagnetic active indexes Dst ≤ -30 nT,Kp≥3 and AE≥ 200 nT, the quiet global distributions of power intensity spectrum of VLF wave, and the corresponding statistical error, were displayed for different seasons in both the dayside and the nightside. By using the power spectral global distribution background, the spectrum characteristics, seasonal variations and geomagnetic active responses of the VLF wave were analyzed statistically. The magnetic VLF wave observation in the solar synchronous orbit can also be sensitive to the magnetic anomalies produced from the Earth. At the frequency channel of 15 kHz and 17. 5 kHz, the south Atlantic magnetic anomaly contour was presented clearly with the power spectral enhancement under the global background. The Bermuda geomagnetic anomalies caused VLF wave power spectral increase in almost all spectral bands at the nighttime, and showed about similar geomagnetic active responses as observed at higher latitude. Especially in the frequency band 12. 5 - 17. 5 kHz, we found that the power spectral increase along the edge of geographical plates, which will enhance our search for ionospheric seismo-response caused by the plate motion, and accumulate experiential background references for such anomalous signal identification quantitatively.