The lifetime of radiation belt protons with energies between 1 kev and 1 Mev

199

136

The characteristic features of the initial enhancement of the storm time ring current particles in the evening hours are consistent with flow patterns resulting from a combination of inward convection, gradient drift, and corotation, which carries plasma sheet protons into low L values near midnight and the higher‐energy proton component into the plasmasphere and through the evening hours. Data from four magnetic storms during the early life of S³‐A (Explorer 45) when the local time of apogee was in the afternoon and evening hours show that protons with lower magnetic moments penetrate deeper into the magnetosphere until a lower limit, determined by the corotation and gradient drift forces, is reached. Such particle motions produce the stable energy‐dependent inner boundary of the ring current protons inside the plasmapause in the dusk sector and also provide the mechanism for energy injection into the ring current region. From the analyses of the pitch angle distributions it is evident that charge exchange and wave‐particle interactions are not the dominant causes of this inner boundary. Observations of plasma sheet protons and electrons at altitudes just beyond the measured plasmapause are also consistent with the resulting flow patterns.

Section: Effects Of the Plasmapausementioning

confidence: 98%

Direct observations in the dusk hours of the characteristics of the storm time ring current particles during the beginning of magnetic storms

Smith¹,

Hoffman²

1974

199

136

“…• ring-current decay and calculated charge-exchange lifetimes [Liemohn, 1961] as found by Swisher and Frank [ 1968] and Smith et al [1975] has been challenged by Tinsley [1976] and by Lyons and Evans [1976], partly on the grounds that Liemohn ' s lifetimes are too long (in view of recent results on neu tral hydrogen density ) and partly on the grounds that pitch-an gle distributions of low-energy ions do not behave in agreement wi th calcu lation .…”

Section: Introductionmentioning

confidence: 98%

On the role of charge exchange in generating unstable waves in the ring current

Cornwall¹

1977

We explore the role of charge exchange in generating anisotropy in the ring current during recovery phase inside the plasmapause. A simplified scenario is studied in which the anisotropy evolves from an initially isotropic distribution. Other cases may be easily studied by shifting the time axis. When the anisotropy becomes large enough, the proton ring current just inside the plasmapause will emit ion electromagnetic cyclotron waves (which can cause stable auroral red (SAR) arcs by electron heating) with subsequent destruction of anisotropy in the wave emission process. As long as finite amplitude waves are present, gain and loss of anisotropy will be in rough equilibrium, and the pitch angle distribution will no longer evolve as it would if only charge exchange were operating. The amount of energy lost to the waves is related to the charge exchange loss rate with the aid of quasi‐linear moment equations; it seems to be adequate to power SAR arcs. The role of heavy ions (He+, He++, and O+) is considered; generally, these ions tend to damp the proton‐generated waves. This damping is quite sensitive to the very low energy (<1 keV) portion of the heavy ion distribution function but not to the thermal (electron volt) component. If the heavy ion fraction at beginning of recovery phase is ≥0.2, proton EMC waves will most likely not be generated by charge exchange beginning from initial isotropy.

“…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.…”

Section: Decay Mechanismmentioning

confidence: 99%

Ring current proton decay by charge exchange

Smith

Hoffman

Fritz³

1976

Explorer 45 (S 3 -A) measurements during the recover y phase (,f a moderate magnet;; storm have confirmed that the char g e exchange decay mechanism can account f or the decay of the storm-time proton ring current. The moderate mannetic storm of 24 February 1972 was selected for study since a svi mccric ring current hr , developed and effects due to asymmetric rin g current losses ^o!-a eliminated.In this study it was found that after the initial rapid deca y of the p roton 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 throu q hout the L-value ran g e of 3.5 to 5.0 at the r '-arge exchange decay rate calculated by Liemohn (1961).After several days of decay, the proton fluxes reached a lower limit where an ap p arent equilibrium was maintained, between weak particle source mechanisms and the loss mechanisms, until fresh protons were injected into the rinq curr-nt renion durin q substorms. blhile other proton loss mechanisms may also be operating, the results indicate that charge exchange can entirely account for the storm-time proton ring current decay, and that this mechanism must be considered in all studies involving the loss of proton rinq current particles.