Ring current proton decay by charge exchange

Explorer 45 (S³‐A) measurements during the recovery phase of a moderate magnetic storm have confirmed that the charge exchange decay mechanism can account for the decay of the storm time proton ring current. The moderate magnetic storm of February 24, 1972, was selected for study, since a symmetric ring current had developed and effects due to asymmetric ring current losses could be eliminated. In this study it was found that after the initial rapid decay of the proton flux, which is a consequence of the dissipation of the asymmetric ring current, the equatorially mirroring protons in the energy range 5–30 keV decayed throughout the L value range of 3.5–5.0 at the charge exchange decay rate calculated by Liemohn (1961). After several days of decay, the proton fluxes reached a lower limit where an apparent equilibrium was maintained, between weak particle source mechanisms and the loss mechanisms, until fresh protons were injected into the ring current region during substorms. While other proton loss mechanisms may also be operating, the results indicate that charge exchange is more than sufficient as a particle loss mechanism for the storm time proton ring current decay and that this mechanism must be considered in all studies involving the loss of proton ring current particles.