Protons as the prime contributors to storm time ring current

Berko, F. W.; Cahill, L. J.; Fritz, T. A.

doi:10.1029/ja080i025p03549

Cited by 44 publications

(23 citation statements)

References 16 publications

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“…The updated B is substituted into . Following the calculations of Hoffman and Bracken [1967] and Berko et al [1975], we repeated this procedure three times. Berko et al [1975] showed that the magnetic field calculated with three iterations approached the observed magnetic field.…”

Section: Simulationmentioning

confidence: 99%

“…Following the calculations of Hoffman and Bracken [1967] and Berko et al [1975], we repeated this procedure three times. Berko et al [1975] showed that the magnetic field calculated with three iterations approached the observed magnetic field. We confirmed that three iterations are sufficient because calculations with four or five iterations reach almost the same result as the three‐iteration calculation.…”

Section: Simulationmentioning

confidence: 99%

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Magnetic coupling of the ring current and the radiation belt

et al. 2008

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The magnetic influence of the storm time ring current on high‐energy particles is demonstrated by using a simulation of the ring current incorporating self‐consistent magnetic and electric fields. Observations by the Polar satellite show that the magnetic field is occasionally depressed by 50% or more near the equatorial plane at <6 RE. We call them equatorially magnetic depression events (EMDEs) and focus on the most intense EMDE observed during an intense storm on 22 October 1999. The simulation predicts that under a strong convection electric field, the magnetic field strength is highly depressed around L = 5 by newly injected ions of energy 80 keV or less. The depressed magnetic field causes a significant adiabatic decrease in the high‐energy ion flux at pitch angles near 90° to conserve the first adiabatic invariant. A more tail‐like (shortened) magnetic field line causes an enhancement of the flux at pitch angles near 0° and 180° to conserve the second adiabatic invariant. Consequently, a butterfly‐like pitch angle distribution (PAD) is formed, which agrees with the Polar observation. We propose that the adiabatic process could have acted not only on the high‐energy component of the protons but also on relativistic electrons in the outer radiation belt. This notion is supported by simultaneous Polar observation of relativistic electron fluxes that show a decrease at pitch angles near 90° and a slight increase at pitch angles near 0° and 180°. PADs of protons and electrons can be used to distinguish nonadiabatic processes acting selectively on electrons from adiabatic ones.

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Section: Simulationmentioning

confidence: 99%

Section: Simulationmentioning

confidence: 99%

Magnetic coupling of the ring current and the radiation belt

et al. 2008

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“…Until the recent work by Lyons and Evans (1976) and Tinsley (1916), in which they suggest He + as a significant ion, ring current studies have assumed or stated that hydrogen was the dominant ion composing the ring current (Berko et al, 1975; and others before that). However, 0 + ions have been shown to be the dominant ion species under geomagnetic stormtime conditions at low altitudes (Shelley et al, 1972;Sharp pt al., 197ba,b).…”

Section: Backg;•oundmentioning

confidence: 99%

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

Smith¹,

Bewtra²,

Hoffman³

1981

J. Geophys. Res.

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The analysis of data from the Explorer 45 (S³‐A) electrostatic analyzer in the energy range 5–30 keV has provided some new results on the ring current ion composition. It has been well established that the storm time ring current has a decay time of several days, during which the particle fluxes decrease nearly monotonically. In the past, ring current studies have assumed or stated that hydrogen was the dominant ion in the earth's ring current. By analyzing the measured ion fluxes during the several day storm recovery period and assuming that beside hydrogen other ions were present and that the decays were exponential in nature, we were able to establish three separate lifetimes for the ions. These fitted decay lifetimes are in excellent agreement with the expected charge exchange decay lifetimes for H+, O+, and He+ in the energy and L value range of the data. This inference technique thus establishes the presence of measurable and appreciable quantities of oxygen and helium ions as well as protons in the storm time ring current; we also find indications that He++ may also be present under these same conditions. The existence of additional ions is not ruled out by this technique.

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“…The main carriers of the ring current are thought to be ions with energies of a few keV to hundreds of keV [e.g., Frank, 1967a;Smith and Hoffman, 1973;Berko et al, 1975;Williams, 1981;Krimigis et al, 1985;Daglis et al, 1993]. During quiet times, the ring current mainly consists of protons, while during storm times, O + ions detectors on the Explorer 45 spacecraft and assuming that the measurements were for protons only, showed that at L~4, over~80% of the ring current energy density is contained in protons with energies of~20-300 keV during both quiet times and storm times.…”

Section: Introductionmentioning

confidence: 99%

The evolution of ring current ion energy density and energy content during geomagnetic storms based on Van Allen Probes measurements

et al. 2015

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Enabled by the comprehensive measurements from the Magnetic Electron Ion Spectrometer (MagEIS), Helium Oxygen Proton Electron mass spectrometer (HOPE), and Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instruments onboard Van Allen Probes in the heart of the radiation belt, the relative contributions of ions with different energies and species to the ring current energy density and their dependence on the phases of geomagnetic storms are quantified. The results show that lower energy (<50 keV) protons enhance much more often and also decay much faster than higher‐energy protons. During the storm main phase, ions with energies <50 keV contribute more significantly to the ring current than those with higher energies; while the higher‐energy protons dominate during the recovery phase and quiet times. The enhancements of higher‐energy proton fluxes as well as energy content generally occur later than those of lower energy protons, which could be due to the inward radial diffusion. For the 29 March 2013 storm we investigated in detail that the contribution from O+ is ~25% of the ring current energy content during the main phase and the majority of that comes from <50 keV O+. This indicates that even during moderate geomagnetic storms the ionosphere is still an important contributor to the ring current ions. Using the Dessler‐Parker‐Sckopke relation, the contributions of ring current particles to the magnetic field depression during this geomagnetic storm are also calculated. The results show that the measured ring current ions contribute about half of the Dst depression.

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Protons as the prime contributors to storm time ring current

Cited by 44 publications

References 16 publications

Magnetic coupling of the ring current and the radiation belt

Magnetic coupling of the ring current and the radiation belt

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

The evolution of ring current ion energy density and energy content during geomagnetic storms based on Van Allen Probes measurements

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