Global ULF Waves Excited by Solar Wind Dynamic Pressure Impulses: 2. The Spatial Distribution Asymmetry

Abstract

Asymmetry is a prevalent characteristic in numerous space physics phenomena. In this study, we investigate the statistical properties and spatial variations of ultra-low frequency power globally after positive dynamic pressure pulses, utilizing high-resolution magnetic field data from SuperMAG between 2012 and 2019. Specifically, we focus on the dawn-dusk and north-south asymmetries of Pc2-5 fluctuations. Our analysis reveals that the power enhancement in the Pc2 band at approximately 30° magnetic latitude (MLAT) in the southern hemisphere is attributable to the South Atlantic Anomaly region. At MLAT ≈ 15°, the power of Pc3-5 waves in both hemispheres exhibits a local minimum, which is associated with the strong coupling of compressional and Alfvén waves. Moreover, around MLAT = 60°, the dawnside Pc5 wave power exceeds that on the duskside when the interplanetary magnetic field (IMF) is westward, and the result is reversed when the IMF is eastward. Notably, Pc3-5 wave power from MLAT = 30° to MLAT = 75° in the northern hemisphere is generally higher than that in the southern hemisphere. In regions with MLAT > 75°, which corresponds to the polar cap between 0 and 15 magnetic local time, the power of Pc3 pulsations is higher during summer in the northern hemisphere and higher during winter in the southern hemisphere. These findings underscore the significant role of the solar wind and the IMF in controlling geomagnetic pulsations and further deepen our understanding of the coupling between fluctuations in the ionosphere and the magnetosphere.