Observation of Pc1 Geomagnetic Pulsation by "Zhang Heng No. 1" in North-South Conjugate Ionosphere

[ Instrument R&D of Instrument Network ] Pc1 geomagnetic pulsation refers to low-frequency fluctuations with a frequency of 0.2-5 Hz. It is closely related to geomagnetic activity and most likely occurs during the magnetic storm recovery phase, which corresponds to the ion cyclotron wave (EMIC) in space. Since the discovery of Pc1 pulsation in geomagnetic data in 1936, scientists have conducted a large number of observational studies on the origin and propagation of Pc1 pulsation. However, it is limited by the space observation position, and the effects of polarization reversal, frequency reflection, and cyclotron absorption in the ionospheric cavity during the propagation of EMIC (Pc1) waves. How does the EMIC (Pc1) waves excited in the magnetosphere propagate to The issue of the ground is inconclusive.

During the recovery phase of the magnetic storm on August 27, 2018, the electromagnetic monitoring test satellite "Zhang Heng No. 1" independently developed by the State Key Laboratory of Space Weather at the National Space Science Center of the Chinese Academy of Sciences observed for the first time a Pc1 fluctuation in the conjugate ionosphere between the north and south event. Researchers Gou Xiaochen, Li Lei, Zhang Yiteng, Zhou Bin, etc. of the State Key Laboratory of Space Meteorology immediately used the data of "Zhang Heng No. 1" high-precision magnetometer and electric field instrument, combined with the observation of Swarm satellites and geomagnetic stations to analyze the characteristics and generation of fluctuations. In-depth study of the mechanism.

Studies have shown that "Zhang Heng No. 1" observed Pc1 fluctuations near the ionospheric wave injection source area (L~3). The fluctuations were injected into the north-south ionosphere in the form of Alfvén waves, and exhibited mixed polarization. Comparing the position of the top of the plasma layer, the study speculates that during the recovery phase of the magnetic storm, the top of the plasma layer moves outward, and ion implantation in the equatorial ring current causes cold plasma instability and stimulates EMIC fluctuations. This EMIC (Pc1) wave propagates in the form of Alfvén waves along the lines of magnetic force to the north-south high latitude area to reach the ionosphere, propagates in the ionospheric wave cavity and is observed by multiple ground stations.

"Zhang Heng No. 1" provides direct observation evidence for Pc1 theory. Related results were published in Annales Geophysicae.