On the variability of EMIC waves and the consequences for the relativistic electron radiation belt population

The interactions between electromagnetic ion cyclotron (EMIC) waves and relativistic electrons are influential in diffusing radiation belt electrons into the loss code from which the electrons are lost into the atmosphere. These wave-particle interactions between EMIC waves and electrons with energies of a few MeV or more, depend strongly on wave spectra and plasma properties. Here we study the variability in wave spectra and plasma properties as a function of L* found during Van Allen Probe EMIC observations. These results are used to calculate statistical bounce and drift average diffusion coefficients that include the variation in wave spectra and plasma density as a function of L* and activity by averaging observation specific diffusion coefficients. The diffusion coefficients are included into global radiation belt simulations and the effect of the EMIC waves is explored. The distribution in the plasma frequency to electron gyrofrequency ratio decreases to lower values as L* decreases. As a result, few EMIC waves are able to resonate with 2-3MeV electrons at L* ≤ 3.75 while electrons of the same energy at larger L* are diffused by EMIC waves in high density regions. In comparison, a sufficient number of EMIC waves are able to resonate with higher energy electrons, urn:x-wiley:21699380:media:jgra56873:jgra56873-math-0001MeV, at L* ≥ 3.25 to significantly effect the decay in electron flux. EMIC wave parametrisations of electron diffusion by EMIC waves are compared and solar wind dynamic pressure is found to give the best agreement with Van Allen Probe observations.

Details