Abstract
On 2 February 2018, the China Seismo-Electromagnetic Satellite (CSES) ZhangHeng 01 (ZH-01) was successfully launched, carrying on board, in addition to a suite of plasma and particle physics instruments, a high precision magnetometer package (HPM), able to observe the ultra-low frequency (ULF) waves. In this paper, a night time Pi2 pulsation observed by CSES is reported for the first time. This Pi2 event occurred on 3 September 2018, and began at 14:30 UT (02:37 magnetic local time), when the satellite was in the southern hemisphere between −49 and −13 magnetic latitude (MLAT). Kakioka (KAK) ground station in Japan detected the same Pi2 between 14:30–14:42 UT (23:30–23:42 local time). The Pi2 oscillations in the compressional, toroidal, and poloidal components at the CSES satellite and the H-component at the KAK station are investigated by estimating coherence, amplitude, and cross-phase. We noticed a high degree of similarity between the Pi2 event in the horizontal component at KAK and the ionospheric fluctuations in the compressional component at CSES. This high correlation indicated the magnetospheric source of the Pi2 event. In addition, Pi2 is exhibited clearly in the δBy component at CSES, which is highly correlated with the ground H component, so the Pi2 event could be explained by the Substorm Current Wedge (SCW). This interpretation is further confirmed by checking the compressional component of Van Allen Probe (VAP) B satellite inside the plasmasphere, which, for the first time, gives observational support for an earlier model. This ULF wave observation shows the consistency and reliability of the high precision magnetometer (HPM) equipped by two fluxgate magnetometers (FGM1 and FGM2) onboard CSES.
Highlights
Pi2 magnetic pulsation is an impulsive nightside ultra-low frequency (ULF) wave and it is considered a sensitive indicator to the onset of the geomagnetic substorms within low- and mid-latitudinal regions
Alfvén waves are commonly invoked as the source of Pi2 on the ground, which is known as the field line resonance (FLR) and is linked with Ffield-Aligned Currents (FAC)
We report a Pi2 event observed by China Seismo-Electromagnetic Satellite (CSES) satellite on 3 September 2018, at 14:30 UT
Summary
Pi2 magnetic pulsation is an impulsive nightside ultra-low frequency (ULF) wave and it is considered a sensitive indicator to the onset of the geomagnetic substorms within low- and mid-latitudinal regions. The authors of [20] elucidated a Pi2 wave seen by LEO satellite, called UARS, and on the ground by the low-latitude Kakioka (KAK) station They demonstrated a similarity between the Pi2 event at a low-latitude region in the horizontal H component and ionospheric perturbations in the compressional Bz component. The same authors concluded that the observations give more support for a plasmaspheric cavity mode They showed that night side Pi2 pulsation in the azimuthal component seems to have a good correlation between the ground station and the topside ionosphere. We use the KAK low-latitude ground station as the reference signal relative to those spectral intensities, coherence, and phase of the ionospheric magnetic field observed at the CSES and Van Allen Probe (VAP) satellites.
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