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 (fpe) and the electron gyrofrequency (fce) significantly influences the efficiency of these processes, with electron acceleration being most effective during periods of low fpe/fce. In this study, a combined total of approximately 24.5 years of THEMIS wave data are analyzed to show how chorus wave intensity and spatial location vary with relative frequency, geomagnetic activity and fpe/fce. Results demonstrate that the strongest chorus emissions are observed during active conditions. At these times, equatorial chorus at low relative frequencies (flhr<f<0.1fce) is strongest when fpe/fce is high (fpe/fce>10) primarily in the region 5<L*<8, from 22:00-12:00 MLT. In sharp contrast at high relative frequencies (0.5fce<f<0.7fce), the equatorial chorus is strongest when fpe/fce is low (fpefce<6) mainly in the region 4<L*<6 from 21:00-09:00 MLT. At intermediate relative frequencies (0.3fce<f<0.4fce), equatorial chorus is strongest in the region 3.5<L*<8 from 21:00-12:00 MLT. In the off-equatorial region the strongest waves are seen in the frequency range (0.1fce<f<0.3fce) between 5<L*<8 and 06:00-15:00 MLT and again are mostly independent of fpe/fce. 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.

Electromagnetic Ion Cyclotron (EMIC) wave are important for the losses of ultra-relativistic electrons from the Earth's radiation belts. In this work, statistical EMIC diffusion coefficients are calculated from Van Allen Probe A observations of EMIC waves from the entire mission. The diffusion coefficient calculations include the observed L* and activity dependent distributions in plasma density and wave spectra so that the wave-particle interactions modelled are representative of those in the radiation belts. These diffusion coefficients can be included into global radiation belt simulations such as the BAS radiation belt model. The study is published in Ross et al 2021, JGR: Space Physics. Funding was provided by National Environment Research Council Highlight Topic grant NE/P01738X/1 (Rad-Sat), National Environment Research Council grant NE/R016445/1 and NE/R016038/1.

The banded structure of Electromagnetic Ion Cyclotron (EMIC) wave spectra and their resonant interactions with radiation belt electrons depend on the cold ion composition. However, there is a great deal of uncertainty in the composition in the inner magnetosphere due to difficulties in direct flux measurements. Here we determine the sensitivity of electron diffusion by EMIC waves to the cold ion composition. The diffusion coefficients are calculated using collocated EMIC waves spectra and plasma densities observed by Van Allen Probe Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) data, parameterised by Dst, using quasi-linear theory implemented in the Pitch-Angle Diffusion of Ions and Electrons (PADIE) code. Funding was provided by NERC Highlight Topic grant: NE/P01738X/1 (Rad-Sat), NERC grant: NE/V00249X/1 (Sat-Risk) and NERC grant: NE/R016038/1