A Statistical Analysis of Spatial and Temporal Phase Evolution in Intermediate-m Ultra-low Frequency (ULF) Wave Observations Using the Hankasalmi SuperDARN Radar and Magnetometer Data

The characterisation of a ULF wave event over a 3-hour interval (0000-0300 UT) on 13^th May, 2016, studied with the Hankasalmi SuperDARN radar and the IMAGE magnetometer array suggests an equatorward latitudinal and eastward longitudinal phase propagation with an effective azimuthal wave number, m of 13.1 ± 1. The wave has been interpreted as resulting from drifting electrons of energies of 35 ± 5 KeV in a drift resonance condition linked to particle populations from a substorm onset at about 1 hour prior to the wave occurrence. The phase characteristics of this wave seem to evolve at 0200 UT when a distinct Pc4 wave was also observed in the magnetometer data with a poleward latitudinal and a westward longitudinal phase propagation (m of -29.5 ± 1). The Pc4 wave is associated with a second harmonic mode driven by a drift-bounce resonance interaction with proton energies of 10 ± 3 KeV from a separate substorm occurrence. We present a statistical analysis of 18 similar ULF wave events also linked to substorm-injected particle populations using the Hankasalmi SuperDARN radar and IMAGE magnetometer array data.