Effect of thermospheric neutral density upon inner trapped‐belt proton flux

Abstract

We wish to point out that a secular change in the Earth's atmospheric neutral density alters charged‐particle lifetime in the inner trapped radiation belts, in addition to the changes recently reported as produced by greenhouse gases. Heretofore, changes in neutral density have been of interest primarily because of their effect on the orbital drag of satellites. We extend this to include the orbital lifetime of charged particles in the lower radiation belts. It is known that the charged‐belt population is coupled to the neutral density of the atmosphere through changes induced by solar activity, an effect produced by multiple scattering off neutral and ionized atoms along with ionization loss in the thermosphere where charged and neutral populations interact. It will be shown here that trapped‐belt flux J is bivariant in energy E and thermospheric neutral density ρ, as J(E, ρ). One can conclude that proton lifetimes in these belts are also directly affected by secular changes in the neutral species populating the Earth's thermosphere. This result is a consequence of an intrinsic property of charged‐particle flux, that flux is not merely a function of E but is dependent upon density ρ when a background of neutrals is present.