Experimental verification of drift-shell splitting in the distorted magnetosphere

Pfitzer, K. A.; Lezniak, T. W.; Winckler, J. R.

doi:10.1029/ja074i019p04687

Cited by 53 publications

(22 citation statements)

References 12 publications

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“…Satellites have observed butterfly‐like PADs for high‐energy protons and electrons on the nightside [e.g., Pfitzer et al , 1969; West et al , 1973; Baker et al , 1978; 1981a; 1981b; Lyons , 1977; Sibeck et al , 1987; Selesnick and Blake , 2002; Fritz et al , 2003]. Some of them have been attributed to magnetopause shadowing due to the drift trajectories depending on the pitch angle under an asymmetric magnetic field (drift shell splitting) [e.g., Stone , 1963; Roederer , 1967].…”

Section: Discussionmentioning

confidence: 99%

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: Discussionmentioning

confidence: 99%

Magnetic coupling of the ring current and the radiation belt

et al. 2008

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“…Those are “butterfly” distributions, or “parallel” or “cigar” distributions. In the outer electron radiation belt it is standard to see butterfly or parallel equatorial pitch angle distributions on the nightside [e.g., Kaye et al , 1978; Selesnick and Blake , 2002; Fritz et al , 2003] and perpendicular equatorial distributions on the dayside [e.g., Pfitzer et al , 1969; Kaye et al , 1978; Selesnick and Blake , 2002].…”

Section: Measurements Of Anisotropy At Geosynchronous Orbitmentioning

confidence: 99%

A survey of the anisotropy of the outer electron radiation belt during high-speed-stream-driven storms

Borovsky

Denton

2011

J. Geophys. Res.

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[1] Electron measurements on board six spacecraft in geosynchronous orbit are superposed-epoch analyzed for 42 high-speed-stream-driven storms. Using pitch angle-resolved fluxes in the range 30 keV to 1.7 MeV, the evolution of the outer electron radiation belt and the suprathermal tail of the electron plasma sheet are studied. The outer electron radiation belt exhibits perpendicular-dominated anisotropies on the dayside and parallel-dominated anisotropies on the nightside consistent with shell splitting in a distorted magnetosphere. The magnitudes of the radiation-belt anisotropies are weak prior to storm onset and become very large during the storms. The magnitudes of the anisotropies lessen with time as the storm ages and the radiation belt heats, probably owing to a weakening of the magnetic field distortion as the storm ages. When a calm before the storm occurs, the dayside radiation belt approaches isotropy, probably owing to pitch angle scattering in the outer plasmasphere that fills during the calm. If no calm before the storm occurs, the dayside radiation belt is strongly perpendicular dominated. The local-time pattern of anisotropy in storms is very different for the suprathermal tail of the electron plasma sheet, which tends to be perpendicular on the nightside and isotropic elsewhere. The magnitudes of the anisotropies of the suprathermal tail are a factor of ∼10 weaker than the anisotropies of the outer electron radiation belt.Citation: Borovsky, J. E., and M. H. Denton (2011), A survey of the anisotropy of the outer electron radiation belt during high-speed-stream-driven storms,

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“…The occurrence of this PAD in the magnetosphere was first described by West (1966), which was a result of upper atmospheric nuclear experimentation in 1962. Since then, the butterfly PAD has been found in naturally occurring populations in both electrons and ions and were reported by Serlemitsos (1966), Pfitzer et al (1969), Bogott and Mozer (1971), West et al (1973), West and Buck (1974), Kaye et al (1978) and Fritz et al (2003) among others.…”

Section: Introductionmentioning

confidence: 99%

Characterising electron butterfly pitch angle distributions in the magnetosphere through observations and simulations

Klida

Fritz

2013

Ann. Geophys.

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The Imaging Electron Spectrometer (IES) on the Polar satellite has measured the average characteristics of the equatorial electron pitch angle distributions (PADs) in the midnight sector as a function of radial distance out to the 9 RE apogee of the Polar satellite. Depressions in the observed fluxes of electrons occur with pitch angles around 90° in the equatorial zone, while the more field-aligned electrons remain largely unchanged. The orbital precessions of the satellite have allowed much of the inner equatorial magnetosphere to be observed. Statistically, butterfly PADs with different shapes are observed selectively in different regions, which can provide insight to their source and possible history. Electron paths of varied pitch angles were modelled using Runge-Kutta approximations of the Lorentz force in a Tsyganenko (T96) simulated magnetosphere. The resulting drift paths suggest that the process of magnetopause shadowing plays a significant role in the loss of these electrons. Case studies of the drifting patterns of electrons with varied pitch angles were simulated from Polar's orbit when a butterfly PAD was observed on 3 October 2002 at an altitude near 9 RE and on 12 September 2000 at an altitude near 6 RE. These two locations represent regions on each side of the boundary of stable trapping. The modelling effort strongly suggests that magnetopause shadowing does play a significant role in the loss of equatorially drifting electrons from the outer regions of the inner magnetosphere

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Experimental verification of drift-shell splitting in the distorted magnetosphere

Abstract: Data from an elect= sW,, :trcxY eter on the syndhrono s orbit satellite TS-1 and data from act electron spectza ter and ion cbaAber on tM elliptical orbit satellite X111 can be used to expP

Cited by 53 publications

References 12 publications

Magnetic coupling of the ring current and the radiation belt

Magnetic coupling of the ring current and the radiation belt

A survey of the anisotropy of the outer electron radiation belt during high-speed-stream-driven storms

Characterising electron butterfly pitch angle distributions in the magnetosphere through observations and simulations

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