Abstract Whistler‐mode chorus waves play a key role in driving radiation belt dynamics by enabling both acceleration of electrons to relativistic energies as well as their loss into the atmosphere via pitch‐angle scattering. The ratio between the electron plasma frequency () and the electron gyrofrequency () significantly influences the efficiency of these processes, with electron acceleration being most effective during periods of low /. In this study, a combined total of approximately 24.5 years of Time History of Events and Macroscale Interactions during Substorms (THEMIS) wave data are analyzed to show how chorus wave intensity and spatial location vary with relative frequency, geomagnetic activity and /. Results demonstrate that the strongest chorus emissions are observed during active conditions (AE > 200 nT). At these times, equatorial chorus at low relative frequencies ( 10) primarily in the region 5 < L * < 8, from 22:00–12:00 MLT. In sharp contrast at high relative frequencies (0.5 < f < 0.7 ), the equatorial chorus is strongest when / is low (/ < 6) mainly in the region 4 < L * < 6 from 21:00–09:00 MLT. At intermediate relative frequencies (0.3 < f < 0.4 ), equatorial chorus is strongest in the region 3.5 < L * < 8 and are largely independent of / from 21:00–12:00 MLT. In the off‐equatorial region the strongest waves are seen in the frequency range (0.1 < f < 0.3 ) between 5 < L * < 8 and 06:00–15:00 MLT and again are mostly independent of /. We show that the location of the strongest waves can be largely explained in terms of the source electrons being in the required energy range for resonance and the absence of Landau damping and highlight the regions where electron acceleration to relativistic energies is likely to be mostly significant.
Bunting et al. (Wed,) studied this question.