Solar wind control of ultralow‐frequency wave activity at L = 3

This study explores the statistical relationships between 2 years of solar wind data recorded by the IMP 8 spacecraft and data from the Mount Clemens magnetometer station (L = 3) to improve our understanding of possible energy sources of ULF wave activity. Within the four frequency bands, f = 4–8 mHz, 8–16 mHz, 16–32 mHz, and 32–64 mHz, that are studied, two distinct types of waves are found. One is at high frequencies corresponding to Pc3 pulsations, and the other is at low frequencies corresponding to Pc5 and low‐frequency Pc4 pulsations. The high‐frequency part clearly has an energy source in the upstream foreshock. However, our analysis shows that the magnetospheric cusps do not appear to be the conduit of energy for the wave activity in this low‐latitude region. The low‐frequency activity occurs most frequently and has greater wave power when the interplanetary magnetic field is southward. This correlation suggests that the major energy source of these low‐frequency waves is substorm‐related or is related to the reconnection on the dayside magnetopause.