Simultaneous ground-based observations of electric and magnetic field variations near the magnetic equator

Abstract

In order to clarify the global nature of penetration mechanism of DP2 electric fields from the polar to the equatorial ionosphere, simultaneous magnetic and electric field observations were carried out using the magnetometer network and HF (High Frequency) radar. The Frequency Modulated - Continuous Wave (FM-CW) HF radar with ionosonde mode was operated to deduce the ionospheric electric fields of DP2 variations at the dip equator, Cebu, the Philippines. Magnetic field variations are also observed simultaneously at the dayside and nightside dip-equator stations of the Circum-pan Pacific Magnetometer Network (CPMN). It is found that the observed DP2 magnetic variations and estimated azimuthal ionospheric electric fields are well correlated in the daytime. Amplitudes of DP2 magnetic variations are very small and/or negligible in the nighttime, but the ionospheric electric field variations in the nighttime are found to be well correlated to DP2 magnetic variations observed in the daytime. This result suggests that the ionospheric field variations of DP2 are not in the zonal, but oriented in the dusk to dawn (or vice versa) direction in the equatorial region.

極域から赤道域までの電離圏におけるDP2電場の地球規模の特性を明らかにするため電場と磁場の同時観測を磁力計およびHF(高周波)レーダを用いて行った。イオンゾンデ型のFM-CW(周波数変調・連続波)HFレーダを操作し伏角赤道(フィリピンセブ島)におけるDP2変動の電離圏電場を測定した。伏角赤道における昼側および夜側の磁場変動も同時に還太平洋磁力計ネットワーク(CPMN)によって観測した。観測したDP2磁気変動と推定された方位電離圏電場は日中において良い相関が見られた。夜間のDP2磁気変動の振幅は極めて小さいかあるいはほとんど無視できるほどであったが、夜間の電離圏電場の変動は昼間に観測されたDP2磁場変動と良い相関があった。この結果は、DP2電離圏場の変動はzonalでなく夕側から夜明け側(あるいはその逆)の方向に方向性があることを示唆している。