Low Frequency ULF Waves in the Earth's Inner Magnetosphere: Power Spectra During High Speed Streams and Quiet Solar...

Here, we extend the scope of the Gamayunov and Engebretson (2021, hereinafter Paper 1), https://doi.org/10.1029/2021JA029247 work by analyzing the low frequency ultra-low-frequency (ULF) wave power spectra in the Earth's inner magnetosphere during high speed stream (HSS) and quiet solar wind (QSW) driving conditions in the upstream solar wind (SW) and comparing our results to the results of Paper 1, where the statistics of ULF wave power spectra during coronal mass ejections (CMEs) are presented. The most important results of our statistical and comparative analyses are as follows. (a) During CMEs, HSSs, and QSW, the magnetic field power spectra of the transverse and compressional fluctuations are well approximated by power laws in the ∼mHz-Hz frequency range, where on average the parameters of power law fits during CMEs and HSSs are close, and those during QSW differ considerably from the respective parameters during CMEs and HSSs. (b) The dominance of the average compressional power over the average transverse power for the low frequency ULF waves during the 0 < SYM/H ≲ 25 nT geomagnetic conditions may serve as a proxy of HSSs in the upstream SW, whereas the opposite relation between the average powers is an indication of CMEs. (c) Independently of the SW driving conditions, a turbulent energy cascade from low frequencies in the ULF wave frequency range into the higher frequency range exists in the Earth's inner magnetosphere, supplying the nonthermal electromagnetic seed fluctuations needed for the growth of electromagnetic ion cyclotron waves (∼Hz) due to relaxation of unstable distributions of energetic magnetospheric ions.