Fig. 5: Statistical properties of AKR precursors and wave-like aurora forms.
From: Radio emissions reveal Alfvénic activity and electron acceleration prior to substorm onset
a Time duration distributions of AKR precursors (blue) and wave-like aurora (green) associated with regular substorms. b Time duration distributions of AKR precursors (blue) and wave-like aurora (green) associated with pseudo-storms. c Frequency and inferred source altitude distribution of AKR precursors (including both substorm and pseudo-storm events). The red histogram shows the frequency distribution of the precursors, while the blue histogram presents the corresponding source altitudes, derived by tracing magnetic field lines from typical wave-like aurora form locations using the IGRF model. d Duration and propagation distance of frequency-drifting tones along magnetic field lines (substorm and pseudo-storm events combined). The red bars denote the durations, and the blue bars represent estimated travel distances. e Frequency drift rates (df/dt) of the precursor tones (blue) and the corresponding inferred drift velocities (red), assuming the source motion along magnetic field lines. Shaded background regions indicate characteristic velocities in the source region: Alfvén speed (purple), proton acoustic speed (light blue), and oxygen ion acoustic speed (light orange), as estimated from plasma parameters described in the Methods. f Periodicity of repetitive frequency-drifting tones in AKR precursors (substorm and pseudo-storm events combined). The red histogram indicates the observed periodicities. Shaded regions show the typical period ranges of auroral beads from previous studies (blue14, green20) and ultra-low frequency (ULF) waves associated with auroral beads (purple11), for comparison. Source data are provided as a Source Data file.
