Analysis of ground-based very low frequency signal recorded onboard CSES satellite

We report on the wave spectral intensity variations associated to very low frequency (VLF) signal observed during the minimum of solar cycle 25. The VLF signal is emitted by the ground-based NWC radio station localized in the southern hemisphere, at −21.5°S and 114°E. The variation of NWC radio signals is daily detected by the electric field experiment EFD onboard the China Seismo-Electromagnetic Satellite (CSES). This satellite has an altitude of about 507 km in a polar and circular sun-synchronous orbit with local time nodes of 02 LT and 14 LT. We study the spectral intensity variations at the frequency of 19.79 kHz in three specific regions: above the NWC station, around the magnetic equatorial plane, and at the conjugate point. We analyze the electric flux above those key regions and estimate the corresponding intensity levels.