Drift shell bifurcation near the dayside magnetopause in realistic magnetospheric magnetic fields

Wan, Yifei; Sazykin, S.; Wolf, R. A.; Ozturk, Mesude

doi:10.1029/2010ja015395

Cited by 12 publications

(24 citation statements)

References 25 publications

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“…This contradicts the conclusions of Wan et al [2010], who suggested that the dominant effect is caused by the east-west asymmetry in the magnetic field which produces large adiabatic (independent of the bounce phase) changes in the invariant. To validate our qualitative conjecture we ran the following numerical experiments illustrated in Figures 5 and A2a.…”

Section: The Structure and Mechanics Of Drift Orbit Bifurcationscontrasting

confidence: 54%

“…[13] We first determine the extent of drift orbit bifurcations in the outer electron belt. The range of drift shells affected by bifurcations depends on the solar wind and geomagnetic conditions controlling the geomagnetic field [Wan et al, 2010]. Bifurcations are most sensitive to the value of the solar wind dynamic pressure (P dyn ), which controls the daynight asymmetry of the field.…”

Section: The Extent Of Drift Orbit Bifurcationsmentioning

confidence: 99%

“…We use Hamiltonian equations of relativistic guiding center motion (Appendix B), which conserve the energy and adiabatic invariants better [e.g., Cary and Brizard, 2009;Wan et al, 2010] than classical guiding center formulations [e.g., Northrop, 1963]. While our Hamiltonian formulation is valid for all realistic magnetospheric conditions including large E × B drift, all computations in this paper are conducted in a static magnetic field, in which case the equation system reduces to the approximation derived by Brizard and Chan [1999]:…”

Section: The Extent Of Drift Orbit Bifurcationsmentioning

confidence: 99%

“…Another effect which adds to the complexity of outer belt dynamics is drift orbit bifurcations, also referred to as Shabansky orbits after Shabansky [1971]. Known for a long time [Northrop and Teller, 1960;Northrop, 1963;Roederer, 1970;Antonova et al, 2003], it recently received renewed attention [Öztürk and Wolf, 2007;Kim et al, 2008;McCollough et al, 2010;Wan et al, 2010] due to development of new particle tracing techniques and improved geomagnetic field models. In this paper we investigate the implications of drift orbit bifurcations for acceleration, transport and loss of the outer belt electrons.…”

Section: Introductionmentioning

confidence: 99%

“…Particles that undergo drift orbit bifurcations (blue color) violate the second invariant J at bifurcations, when the period of the bounce and the drift motions are no longer separated. This drives pitch angle and radial transport even when the magnetic field is constant [e.g., Antonova et al, 2003;Öztürk and Wolf, 2007;Wan et al, 2010]. Since the second invariant is not conserved, the drift orbits are not closed and the third invariant is undefined.…”

Section: Introductionmentioning

confidence: 99%

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The role of drift orbit bifurcations in energization and loss of electrons in the outer radiation belt

et al. 2011

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[1] Radiation levels in Earth's outer electron belt (L^2.5) vary by orders of magnitude on the time scales ranging from minutes to days. Multiple acceleration and loss processes operate across the belt and compete in defining its global variability. One such process is the drift orbit bifurcation effect. Caused by coupling of the drift and bounce motions, it breaks the second adiabatic invariant of radiation belt electrons producing their transport in radius and pitch angle. In this paper we investigate implications of drift orbit bifurcations to the global state and variability of the outer electron belt. For this purpose we use three-dimensional test particle simulations of electron guiding center motion in a realistic magnetic field model. We show that even at most quiet solar wind conditions bifurcations affect a broad range of the belt penetrating inside the geosynchronous orbit. This has an important practical implication for the analysis of experimental particle data: since the third adiabatic invariant is undefined for bifurcating orbit, the electron phase space density cannot be expressed in terms of three adiabatic invariants. We show that long-term transport of electrons due to drift orbit bifurcations is a complex combination of large ballistic jumps and small-amplitude diffusion in the second invariant and radial location. To model long-term transport, we derive an empirical map of the second invariant and radial jumps at bifurcations. The map can also be implemented by other radiation belt models, which cannot directly account for the physics of drift orbit bifurcations. Drift orbit bifurcations can produce electron losses through the magnetopause escape and through pitch angle scattering into the atmospheric loss cone. Most electrons, however, can stay quasi-trapped in the bifurcation regions for very long time periods. The pitch angle and radial transport due to drift orbit bifurcations lead to their meandering back and forth across the region producing mixing and recirculation of particle populations with different initial conditions. We show that this recirculation can greatly amplify electron energization by radial diffusion. Compared to the diffusion alone, the combined action of radial diffusion and drift orbit bifurcations can double electron energization at each recirculation cycle. Our results suggest that drift orbit bifurcations can play an important role in the buildup of increased electron fluxes in the storm recovery phase.

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Section: The Structure and Mechanics Of Drift Orbit Bifurcationscontrasting

confidence: 54%

Section: The Extent Of Drift Orbit Bifurcationsmentioning

confidence: 99%

Section: The Extent Of Drift Orbit Bifurcationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The role of drift orbit bifurcations in energization and loss of electrons in the outer radiation belt

et al. 2011

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Enhanced radial transport and energization of radiation belt electrons due to drift orbit bifurcations

et al. 2014

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[1]Relativistic electron intensities in Earth's outer radiation belt can vary by multiple orders of magnitude on the time scales ranging from minutes to days. One fundamental process contributing to dynamic variability of radiation belt intensities is the radial transport of relativistic electrons across their drift shells. In this paper we analyze the properties of three-dimensional radial transport in a global magnetic field model driven by variations in the solar wind dynamic pressure. We use a test particle approach which captures anomalous effects such as drift orbit bifurcations. We show that the bifurcations lead to an order of magnitude increase in radial transport rates and enhance the energization at large equatorial pitch angles. Even at quiet time fluctuations in dynamic pressure, radial transport at large pitch angles exhibits strong deviations from the diffusion approximation. The radial transport rates are much lower at small pitch angle values which results in a better agreement with the diffusion approximation.

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First optical observations of energetic electron precipitation at 4278 Å caused by a powerful VLF transmitter

Denton

Kosch

Borovsky

et al. 2014

Geophys. Res. Lett.

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A summary is presented of experimental optical observations at 4278 Å from close to a powerful (~150 kW) VLF transmitter (call sign JXN) with a transmission frequency of 16.4 kHz. Approximately 2.5 s after transmitter turn-on, a sudden increase in optical emissions at 4278 Å was detected using a dedicated camera/ charge-coupled device (CCD) monitoring system recording at a frequency of 10 Hz. The optical signal is interpreted as a burst of electron precipitation lasting~0.5 s, due to gyro-resonant wave-particle interactions between the transmitted wave and the magnetospheric electron population. The precipitation was centered on the zenith and had no detectable spatial structure. The timing of this sequence of events is in line with theoretical predictions and previous indirect observations of precipitation. This first direct measurement of VLF-induced precipitation at 4278 Å reveals the spatial and temporal extent of the resulting optical signal close to the transmitter.

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Drift shell bifurcation near the dayside magnetopause in realistic magnetospheric magnetic fields

Cited by 12 publications

References 25 publications

The role of drift orbit bifurcations in energization and loss of electrons in the outer radiation belt

The role of drift orbit bifurcations in energization and loss of electrons in the outer radiation belt

Enhanced radial transport and energization of radiation belt electrons due to drift orbit bifurcations

First optical observations of energetic electron precipitation at 4278 Å caused by a powerful VLF transmitter

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