Whistlers on Density Gradients in the Radiation Belts

Near apogee of an orbit in early 2013, the Van Allen Probes spacecraft observed a series of strongly localized, large-amplitude (E > 20 mV/m or B > 2 nT) whistler waves. The leading spacecraft observed waves embedded within deep density cavities while the trailing spacecraft observed waves that appeared to be confined near monotonic density gradients. We use high-resolution EFW burst data from this event to estimate the spectral characteristics of the observed whistlers. We then use these characteristics as input to an electron MHD simulation which demonstrates that the observations are consistent with ducted propagation in the observed density structures.