Polarization and Spatial Distribution Features of Pc4 and Pc5 Waves in the Magnetosphere

Ultra-low frequency waves interact with different particle populations all over the magnetosphere. Some interaction mechanisms are associated with certain wave modes, but is it really so and what about waves interaction between each other? We present a statistical analysis of Pc4 and Pc5 waves in the magnetosphere of the Earth that were observed by Arase satellite from March 2017 to December 2020. These waves were classified by polarization into toroidal, poloidal, and compressional waves. Toroidal and poloidal waves are thought to be Alfven waves that are eigenoscillations of Earth's magnetic field lines. The former are believed to be generated by external sources, while the latter one-by internal sources. We compared spatial distribution features with well-known case studies to reveal their nature for all three polarizations. A high inclination of Arase orbit supported a wave field-aligned structure research. We found that toroidal waves are mostly odd harmonics and poloidal waves are both even and odd harmonics of Alfven waves, while compressional waves were observed in a narrow equatorial region only. Different wave generation mechanisms that cause a clear difference in spatial distributions of toroidal, poloidal, and compressional waves could excite a specific wave polarization. Surprisingly, the statistics of wave polarization has a normal distribution without separate clusters. We suggest that polarization change and mode coupling processes make mixed polarization the most common type of polarization in the magnetosphere. This result raises the question of how the polarization change process affects wave-particle interactions responsible for energy transport throughout the magnetosphere. Energy transport in the magnetosphere of the Earth is a complex process involving different populations of charged particles and electromagnetic waves. The waves classified as Pc4 and Pc5 have a wavelength comparable to the size of the magnetosphere and are responsible for energy transport on a large distance. We collected 46 months of Pc4 and Pc5 waves observations by Arase satellite to find a dependence of wave parameters on excitation source. We divided waves in the data set by magnetic field variation direction into radial, azimuthal, and field-aligned waves. These three types of waves have different spatial distribution in both equatorial and meridional planes. We compared distribution features with specific energy sources using well-known case studies. Surprisingly, wave polarization statistics did not reveal any separation of waves into clusters that could be associated with different sources or wave generation mechanisms. This fact forces us to pay more attention to wave polarization change processes and to a coupling of waves with different polarization to reveal a correct mechanism of energy exchange between the waves and charged particles in the magnetosphere. Transverse waves are mostly mixed polarized, without separate clusters of pure poloidal and toroidal wavesToroidal waves are odd harmonics of field line resonance, while poloidal waves are both odd and even harmonics connected with the ion driftCompressional waves are concentrated at the geomagnetic equator, with two essential maxima of the occurrence rate in L-MLT distribution