The Impact of Plasma Density Gradients on Lower Band Chorus Wave Propagation

Abstract Plasma density gradients, such as those that occur on plasmaspheric plume boundaries, have been shown to increase the obliquity of lower band chorus. Here, for the first time, this relationship is investigated more generally by considering the wave normal angle, , as a function of the magnitude of all observed density gradients. Both case studies, and a statistical analysis, reveal a direct correspondence between the magnitude of density gradients and wave obliquity, with increasing near stronger density gradients. Wave propagation is also investigated as a function of local plasma density, revealing that chorus is more often oblique when observed in lower density mediums, and more field‐aligned in higher density regions. This result highlights the importance of retaining the intrinsic physical coupling between wave propagation properties and the cold plasma density, since both parameters strongly influence the calculation of the diffusion coefficients used to quantify wave‐particle interactions in the inner‐magnetosphere.