The heating of suprathermal ions above thunderstorm cells

Abstract

We estimate ion heating in the topside ionosphere directly over thunderstorm cells. The primary heating is due to lower hybird waves excited through linear mode coupling as intense electromagnetic (EM) whistler mode radiation from lightning is scattered from small scale (2 – 20 m) magnetic‐field‐aligned plasma density irregularities in the topside ionosphere. For typical radiated EM fields, we find that suprathermal H+ ions in the ≥ 6 eV energy range can be heated by 20 to 40 eV as a result of a single lightning discharge. We also show how the number density of ≥ 6 eV H+ ions is enhanced by preheating resulting from the absorption of proton whistlers in the 500 – 1000 km altitude range. For lightning discharge rates of one or more per second over a 104 km² area, our model predicts a total energy gain for the H+ ions of 400 eV to 2 KeV and a perpendicular ion flux of j⟂ ∼ 105 to 106cm−2sec−1. These fluxes should be observable on low altitude spacecraft using presently available instrumentation.