ULF waves observed in solar wind and on the ground at high, mid, and low latitudes

Abstract

We analyze fluctuations of the magnetic field in the solar wind registered by the ACE satellite in the L1 Lagrangian point and the ULF waves observed with ground magnetometers at high, middle, and low latitudes during 84 intense substorm events. Our goal is to establish possible connections between ULF oscillations observed simultaneously in the different parts of the solar wind–magnetosphere–ionosphere system during substorms. Our analysis reveals that there is a good correlation between oscillations with frequencies less than 1 mHz observed in the solar wind and in three different latitudes during strong substorms. In particular, we show that: (1) the dominant frequencies of the waves observed on the ground at high, middle, and low latitudes are approximately the same; (2) the waves with frequencies of 0.45–0.55mHz, and 0.75–0.80mHz are the most often seen in high, middle, and low latitudes and in the solar wind. Therefore, we conclude that there is a strong coupling between the Earth’s magnetosphere–ionosphere system and the solar wind in the frequency range below 1mHz mediated by the disturbances in the magnetic field.