Japan Geoscience Union Meeting 2019

Presentation information

[E] Poster

P (Space and Planetary Sciences ) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM13] Inner magnetosphere: Recent understanding and new insights

Wed. May 29, 2019 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Yusuke Ebihara(Research Institute for Sustainable Humanosphere, Kyoto University), Danny Summers(Memorial University of Newfoundland), Yoshizumi Miyoshi(Institute for Space-Earth Environmental Research, Nagoya University), Shinji Saito(Graduate School of Science, Nagoya University)

[PEM13-P18] Modulation of the D-region ionosphere by Pc5 waves observed by VLF/LF standard radio waves

*Miyashita Takuya1, Hiroyo Ohya1, Fuminori Tsuchiya2, Hiroyuki Nakata1, Toshiaki Takano1, Kazuo Shiokawa3, Yoshizumi Miyoshi3 (1.Chiba University, 2.Tohoku University, 3.Nagoya University)

Keywords:VLF/LF standard radio waves, Pc5, ULF

Ionospheric modulation due to ultra low frequency (ULF) Pc5 waves have been observed by GPS-total electron content (TEC), high frequency (HF) Doppler sounders, and SuperDARN HF radars [e.g., Pilipenko et al., 2014; Belakhovsky et al., 2016]. However, there are few reports for the modulation of the lower ionospheric associated with the ULF Pc5 waves using VLF/LF transmitter signals. In this study, we investigate the D-region signatures of the modulation due to the ULF Pc5 waves using a network of very low frequency (VLF)/low frequency (LF) standard radio waves. We show oscillations in intensities of the VLF/LF waves with a period of 4-6 minutes during substorms on 27 April, 2017. The transmitter signals from NAA (USA, 24.0 kHz, L = 2.88), NLK (USA, 24.8 kHz, L = 2.88), NDK (USA, 25.2 kHz, L = 2.98) and WWVB (USA, 60.0 kHz, L = 2.26) were observed by the receivers at ATH (Athabasca, L=4.31) and PKR (Poker Flat, L=5.95). The substorm occurred at 04:30 UT. Based on the wavelet analysis, we found that the intensities for the NDK-ATH and WWVB-ATH paths showed oscillations with a period of 4-6 minutes during the substorm growth phase (05:00-06:00 UT). Magnetic field variations observed by ground magnetometers around the NDK-ATH and WWVB-ATH paths also showed the same periodicity, which means that the variations in the VLF/LF intensities would be caused by Pc5 modulations. The magnetic field oscillations were observed in wide latitude range. The intensity of the oscillation was larger at high latitude magnetometers than those around the location of the NDK-ATH and WWVB-ATH path (mid-latitude). The Pc5 oscillations could be excited by solar wind because solar wind speed had similar period of the 4-6 minutes. In this presentation, we will discuss the cause of these VLF/LF oscillations.