Precipitation of radiation belt electrons induced by obliquely propagating lightning‐generated whistlers

Abstract

A new combined ray tracing and test particle formulation is presented which calculates the spatiotemporal electron precipitation flux signatures at ionospheric altitudes induced by obliquely propagating lightning‐generated whistler waves. The formulation accounts for the variation in wave characteristics (frequency‐time dispersion, wave normal angle, and power density) as the whistler generated by an individual lightning discharge propagates through vast volumes of the magnetosphere in the absence of field‐aligned cold plasma density enhancements, and calculates the detailed gyroresonance scattering of trapped energetic electrons into the atmospheric loss cone over a broad range of field lines (L shells) to determine the precipitation flux over extensive ionospheric regions. Results show that peak precipitation flux patches (hotspots) several tens of degrees of latitude and longitude in size develop at locations ∼7° to ∼20° poleward of the discharge as a consequence of propagation paths which convey wave energy from lower to higher L shells. For oblique whistler intensities matching satellite observations (10 to 30 pT) peak flux levels of several milli‐ergs cm−2 s−1 are indicated, arriving as early as ∼ 1/4 s and lasting ∼1/2 s at lower observing latitudes (e.g., ∼32° for North American longitudes), while being delayed to ∼l s or more and lasting up to ∼2 s at higher latitudes (∼47°), creating a sense of poleward hotspot motion. Summary profiles integrated over time, latitude and L shell suggest that lightning‐generated oblique whistler‐induced electron precipitation deposits appreciable energy to the upper atmosphere at midlatitudes and contributes significantly to the loss of energetic (>100 keV) radiation belt electrons, particularly over 2.2 ≤ L ≤ 3.5 where the slot region forms.