The spatio-temporal characteristics of ULF waves driven by substorm injected particles

A previous case study observed a ULF wave with an eastward and equatorward phase propagation (an azimuthal wave number m, of approximate to 13) generated during the expansion phase of a substorm. The eastward phase propagation of the wave suggested that eastward drifting energetic electrons injected during the substorm were responsible for driving that particular wave. In this study, a population of 83 similar ULF wave events also associated with substorm-injected particles have been identified using multiple Super Dual Auroral Radar Network radars in Europe and North America between June 2000 and September 2005. The wave events identified in this study exhibit azimuthal wave numbers ranging in magnitude from 2 to 92, where the direction of propagation depends on the relative positions of the substorm onsets and the wave observations. We suggest that azimuthally drifting energetic particles associated with the substorms are responsible for driving the waves. Both westward drifting ions and eastward drifting electrons are implicated with energies ranging from approximate to 1 to 70 keV. A clear dependence of the particle energy on the azimuthal separation of the wave observations and the substorm onset is seen, with higher energy particles (leading to lower m-number waves) being involved at smaller azimuthal separations.