Magnetic field drift shell splitting: Cause of unusual dayside particle pitch angle distributions during storms and substorms

Sibeck, D. G.; McEntire, R. W.; Lui, A. T. Y.; López, Ramón; Krimigis, S. M.

doi:10.1029/ja092ia12p13485

Cited by 146 publications

(168 citation statements)

References 52 publications

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“…Early surveys of energetic electrons consistently found pancake distributions inside 6-9 R E (1 R E = 6370 km), while butterfly or isotropic distributions appeared outside [e.g., West et al, 1973;Lyons and Williams, 1975]. The trapping distributions of the inner magnetosphere largely result from inward diffusion that preserves the first and second adiabatic invariants [e.g., Schulz and Lanzerotti, 1974], while the butterfly distributions in the outer magnetosphere were explained largely as effects of magnetic drift shell splitting or the negative gradient in the radial flux, possibly in combination with wave-particle scattering and often during disturbed conditions [e.g., Roederer, 1970;Lyons and Williams, 1975;Sibeck et al, 1987;Horne et al, 2003]. Both unidirectional and bidirectional distributions of energetic electrons were commonly observed in the magnetotail and associated with acceleration events in the magnetotail plasma sheet as well as open/closed field topology [e.g., Stone, 1976, 1977].…”

Section: Introductionmentioning

confidence: 99%

Pitch angle distributions of energetic electrons at Saturn

et al. 2011

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[1] Pitch angle distributions of energetic electrons (110-365 keV) at Saturn are statistically analyzed for [2005][2006][2007][2008][2009]. Using a nondipolar model magnetic field, pitch angle distributions are mapped to the magnetospheric equator and sorted by equatorial crossing distance. The results are quantified using a standard function for the pitch angle distribution, f(a) = Asin K a (where a is the pitch angle and K is the power). Inside of ∼10 R S , the distributions are mostly peaked at 90°(K < 0), signifying a trapping distribution. Outside of this distance, the distributions are mostly field aligned (K > 0) with maxima near 0°and 180°. The 10 R S boundary maps to Saturn's ionosphere at latitudes equatorward of the aurora. Very few "flat" distributions are observed (K ≈ 0). The pitch angle distributions are not as well organized in local time as they are in radial distance, but over the 5 year survey between 10 and 20 R S field-aligned distributions appear most often near midnight, while trapping distributions are found elsewhere.

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Section: Introductionmentioning

confidence: 99%

Pitch angle distributions of energetic electrons at Saturn

et al. 2011

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“…Those energetic ions and electrons could be injected at local midnight and drift toward the dayside. Due to drift shell splitting, ring current ion fluxes with an anisotropic pitch angle distribution are enhanced in the afternoon sector (Sibeck et al, 1987). With density enhancements of cold ions, the anisotropic RC proton distributions can become unstable so as to easily excite EMIC waves (Gary et al, 1995).…”

Section: Discussionmentioning

confidence: 99%

Energetic ions scattered into the loss cone with observations of the Cluster satellite

2016

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Abstract. In this paper, we report in situ observations by the Cluster spacecraft of energetic ions scattered into the loss cone during the inbound pass from the plasma sheet into the plasmasphere. During the inbound pass of the plasma sheet, Cluster observed the isotropy ratio of energetic ions to gradually decrease from unity and the isotropic boundary extended to lower L value for higher-energy ions, implying that the field line curvature scattering mechanism is responsible for the scattered ions into the loss cone from the plasma sheet. In the outer boundary of a plasmasphere plume, Cluster 3 observed the increase of the isotropy ratio of energetic ions accompanied by enhancements of Pc2 waves with frequencies between the He + ion gyrofrequency and O + ion gyrofrequency estimated in the equatorial plane. Those Pc2 waves were left-hand circularly polarized and identified as electromagnetic ion cyclotron (EMIC) waves. Using the observed parameters, the calculations of the pitch angle diffusion coefficients for ring current protons demonstrate that EMIC waves could be responsible for the ions scattering and loss-cone filling. Our observations provide in situ evidence of energetic ion loss in the plasma sheet and the plasmasphere plume. Our results suggest that energetic ions scattering into the loss cone in the central plasma sheet and the outer boundary of the plasmaspheric plume are attributed to the field line curvature scattering mechanism and EMIC wave scattering mechanism, respectively.

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“…Previously, Kosik (1979) reported that during a magnetically quiet period the convection electric field is very weak and the magnetic field asymmetry produces the dominant effect. Sibeck et al (1987) further showed that compared to gradient and curvature drifts the electric drifts are negligible for the >25 keV particles. Therefore, for the present particle trajectory traces, an E=0 electric field was assumed along with the T96 model.…”

Section: Trajectory Generatormentioning

confidence: 99%

“…These butterfly distributions were caused by the Russian high-altitude nuclear detonation on 28 October 1962. Various reasons for the natural occurrence of butterfly distributions have been given in literature; such as drift shell splitting (Roederer, 1967(Roederer, , 1970 and either magnetopause shadowing (West et al, 1972(West et al, , 1973 or a negative radial flux gradient (Pfitzer et al, 1969;Sibeck et al, 1987).…”

Section: Introductionmentioning

confidence: 99%

Implications of unusual pitch-angle distributions observed by ISEE-1 and 2

et al. 2006

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Abstract. Unusual energetic particle pitch angle distributions (PADs) were observed by the ISEE-1 and 2 satellites at 3 h MLT and a radial distance of about 10-15 R E during the time period of 07:00-14:00 UT on 3 March 1979. The ISEE-1 satellite obtained complete 3-D distributions of energetic proton and electron fluxes as a function of energy, while ISEE-2 was configured to provide higher time resolution but less angular resolution than ISEE-1. The ISEE-1 observed a butterfly PAD (a minimum in the 90 • PA particle flux) for a period of about 2 h (10:00-12:00 UT) for the electrons, and 3 h (09:00-12:00 UT) for the protons over an energy range of 22.5-189 keV (E1-E4) for the electrons and 24-142 keV (P1-P4) for the protons. The small pitch angle (15 • , 30 • ) charged particles (electrons and protons) are seen to behave collectively in all four energy ranges. The relative differences in electron fluxes between 15 • PA and 90 • PA are more significant for higher energy channels during the butterfly PAD period. Three different types of electron PADs (butterfly, isotropic, and peaked-at-90 • ) were observed at the same location and time as a function of energy for a short period of time before 10:00 UT. Electron butterfly distributions were also observed by the ISEE-2 for about 1.5 h over 28-62 keV (E2-E4), although less well resolved than ISEE-1. Unlike the ISEE-1, no butterfly distributions were resolved in the ISEE-2 proton PADs due to less angular resolution. The measured drift effects by ISEE-1 suggest that the detected protons were much closer to the particle source than the electrons along their trajectories, and thus ruled out a nightside source within 18:00 MLT to 03:00 MLT. Compared to 07:30 UT, the charged particle fluxes measured by ISEE-1 were enhanced by up to three orders of magnitude during the period 08:30-12:00 UT. From 09:10:00 UT to 11:50 UT, the geomagnetic conditions were quiet (AE<100 nT), the LANL geosynchronous satellites observed no substorms, and the loCorrespondence to: T. A. Fritz (fritz@bu.edu) cal magnetic field measured by ISEE-1 was almost constant, while the small PA charged particle (both electron and proton) fluxes measured by ISEE-1 increased gradually, which implies a particle source other than the substorm source. Based on detailed particle trajectory tracings in a realistic geomagnetic field model, the 50-200 keV protons with small PA at 10:00 UT ISEE-1 location on 3 March 1979 were passing through the northern high-altitude and high-latitude morningside region where the cusp should be located under a dawnward IMF component condition, while those protons with large PA may connect to the high-latitude morningside magnetopause. It is possible that the cusp source is responsible for the all particles observed during the event.

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Magnetic field drift shell splitting: Cause of unusual dayside particle pitch angle distributions during storms and substorms

Cited by 146 publications

References 52 publications

Pitch angle distributions of energetic electrons at Saturn

Pitch angle distributions of energetic electrons at Saturn

Energetic ions scattered into the loss cone with observations of the Cluster satellite

Implications of unusual pitch-angle distributions observed by ISEE-1 and 2

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