Highly Oblique Lower-Band Chorus Statistics: Dependencies of Wave Power on Refractive Index and Geomagnetic Activity

We use 3 years of Van Allen Probes observations of highly oblique lower-band chorus waves at low latitudes over L = 4\textendash6 to provide a comprehensive statistics of the distribution of their magnetic and electric powers and full energy density as a function of wave refractive index N, L shell, and geomagnetic activity AE. We use the refractive index calculated either in the cold plasma approximation or in the quasi-electrostatic (hot plasma) approximation and either observed wave electric fields or corrected wave electric fields accounting for the formation of a plasma sheath around antenna probes in a low-density plasma. Approximate fits to the maximum refractive index and to the magnetic wave power profile of highly oblique waves are provided as a function of AE and L. Such fits should be useful for simulations of quasi-linear electron diffusion induced by very oblique chorus waves. The magnetic wave power of these oblique waves remains elevated and roughly constant up to higher N values at lower L < 5 and during less disturbed periods AE*<200 nT, likely due to the corresponding lower temperature of hot electrons injected from the plasma sheet, which leads to weaker thermal effects and Landau damping of these very oblique waves. The average energy density of lower-band chorus waves is mainly distributed from N = 30\textendash50 up to N = 150\textendash300, mostly corresponding to highly oblique waves even at low magnetic latitudes.
Year of Publication
Journal of Geophysical Research: Space Physics
Date Published