Lifetimes for low-energy protons in the outer radiation zone

Abstract

The directional, differential intensities of protons over the energy range ∼200 ev to 50 key injected into the outer radiation zone (i.e., the extraterrestrial ring current) coincident with the initial phase of the geomagnetic storm during early July 1966 were monitored with a sensitive array of electrostatic analyzers borne on the earth satellite OGO 3. Proton intensities are greatly enhanced throughout the outer radiation zone for L values ≳3 during the main phase of this moderate magnetic storm, and the injection mechanism ceases to be effective after the storm main phase for L values ≲5.5. Proton (30 ≤ E ≤ 50 kev) intensities are shown to exponentially decay with lifetimes ranging from 15 to 105 hours in substantial agreement with calculated lifetimes invoking measured charge‐exchange cross sections for protons incident upon atomic hydrogen and a model of the atomic hydrogen concentration in the earth's exosphere. The atomic hydrogen concentration model for the terrestrial exosphere providing the best fit to the observed proton lifetimes over geocentric radial distances 2.5–4.8 RE (corresponding to observed concentrations ∼200 to 30 hydrogen atoms/cm³) allows only atoms in ballistic orbits in the exosphere as opposed to a model geocorona that includes an additional atomic hydrogen population in captive elliptical orbits.

Local time variations of particle flux produced by an electrostatic field in the magnetosphere

“…Previous interpretations [Cornwall et al, 1970] of Frank's [1970a] results have favored the view that strong dissipative mechanisms result in proton precipitation in the afternoon sector, thus reducing the flux of particles that drift to the noon meridian. Cornwall et al [1970] note that known loss mechanisms, such as charge exchange, previously calculated by Swisher and Frank [1968], are not adequate to explain Frank's results. They suggest that ion cyclotron resonance with waves whose amplitude is not experimentally known could account for the asymmetries of the ring current proton flux.…”

Ring current proton decay by charge exchange

“…The predicted values which were used are the lifetimes calculated by Liemohn (1961) for the ring current altitudes and rinn c-rent energies. This reference has been used consistently in previous wn O (Frank, 1967;Swisher and Frank. 1968;Russell and Thorne, 1970) on the charge exchange question and was therefore selected on the basis of its historical merit.…”

“…•harge exchange of the ring current protcns with neutral hydrogen appear o be the primary loss mechanism for the tens of keV protons (Frank, 1967;Swisher and Frank, 1968). With the more re-ent theories and observations pointing to additional mechanisms occurring in the ring current region, it is important to establish the fact that the measurements from…”

Inference of the ring current ion composition by means of charge exchange decay

“…The long term decay times of several days for the measured fluxes were consistent 4ith the available charge exchange lifetimes and, therefore, supported the charge exchange position (Frank, 1967;Swisher and Frank, 1968). These favorable comparisons were based on the early computational work by Liemohn (1961), who specified both the mean lifetime, c e , for protons confined to the equatorial plane and the charge exchange lifetime, lm, for protons mirroring off the geomagnetic equator.…”