Speaker
Description
Electromagnetic ion cyclotron (EMIC) waves are generated in the equatorial regions of the inner magnetosphere. These waves propagate to the middle or low latitudes in the ionosphere through the ionospheric duct, detected as Pc1 waves by ground-based magnetometers. To figure out how the Pc1 wave power attenuates during propagation in space and on the ground, we investigated a magnetically conjugate Pc1 wave event occurring around 07:00 Universal Time (UT) on January 8, 2018, using data obtained from the Arase satellite and the four PWING ground-based magnetometers located at Zhigansk (ZGN), Magadan (MGD), Moshiri (MSR), and Gakona (GAK). The EMIC waves observed at the Arase satellite were in the helium (He+) band with frequencies of 0.35-0.55 Hz, and the conjugated Pc1 waves were also simultaneously detected within a similar frequency range at the different PWING ground stations. According to polarization analysis of the Pc1 waves, we found that the polarization angles pointed toward the magnetic footprint of the satellite, suggesting that the observed Pc1 wave on the ground and EMIC waves at the Arase satellite were magnetically conjugated. To determine the propagation effect from the source region to each observation point, we calculated wave power attenuation in decibels (dB) relative to the wave power obtained at ZGN. We found that along the ionospheric wave duct, the wave power attenuation factors were 8.22, 5.34, and 4.71 dB/1000 km for the ZGN-MGD, ZGN-MSR, and ZGN-GAK intervals, respectively. Along the magnetic field lines in the magnetosphere, the power attenuation factor was 0.37 dB/1000 km, which can be considered the minimum value. From the results, we suggest that the wave power of Pc1 waves attenuates much less when they propagate in the magnetosphere along magnetic field lines than when they propagate in the ionosphere through ionospheric wave ducts. For future work, we plan to investigate more magnetically conjugate Pc1 wave events using various datasets, including those from geosynchronous orbit satellites and LEO satellites, to statistically examine how the power attenuation changes under different geomagnetic condition.
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