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Found 7 entries in the Bibliography.

Showing entries from 1 through 7


Global MHD test particle simulations of solar energetic electron trapping in the Earth\textquoterights radiation belts

Test-particle trajectories are computed in fields from a global MHD magnetospheric model simulation of the 29 October 2003 Storm Commencement to investigate trapping and transport of solar energetic electrons (SEEs) in the magnetosphere during severe storms. SEEs are found to provide a source population for a newly formed belt of View the MathML source electrons in the Earth\textquoterights inner zone radiation belts, which was observed following the 29 October 2003 storm. Energy and pitch angle distributions of the new belt are compared with results previously obtained [Kress, B.T., Hudson, M.K., Looper, M.D., Albert, J., Lyon, J.G., Goodrich, C.C., 2007. Global MHD test particle simulations of >10 MeV radiation belt electrons during storm sudden commencement. Journal of Geophysical Research 112, A09215, doi:10.1029/2006JA012218], where outer belt electrons were used as a source for the new belt.


Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 11/2008

YEAR: 2008     DOI: 10.1016/j.jastp.2008.05.018

Shock-Induced Transport. Slot Refilling and Formation of New Belts.


Global MHD test particle simulations of >10 MeV radiation belt electrons during storm sudden commencement

[1] Prior to 2003, there are two known cases where ultrarelativistic (≳10 MeV) electrons appeared in the Earth\textquoterights inner zone radiation belts in association with high speed interplanetary shocks: the 24 March 1991 and the less well studied 21 February 1994 storms. During the March 1991 event electrons were injected well into the inner zone on a timescale of minutes, producing a new stably trapped radiation belt population that persisted for \~10 years. More recently, at the end of solar cycle 23, a number of violent geomagnetic disturbances resulted in large variations in ultrarelativistic electrons in the inner zone, indicating that these events are less rare than previously thought. Here we present results from a numerical study of shock-induced transport and energization of outer zone electrons in the 1\textendash7 MeV range, resulting in a newly formed 10\textendash20 MeV electron belt near L \~ 3. Test particle trajectories are followed in time-dependent fields from an MHD magnetospheric model simulation of the 29 October 2003 storm sudden commencement (SSC) driven by solar wind parameters measured at ACE. The newly formed belt is predominantly equatorially mirroring. This result is in part due to an SSC electric field pulse that is strongly peaked in the equatorial plane, preferentially accelerating equatorially mirroring particles. The timescale for subsequent pitch angle diffusion of the new belt, calculated using quasi-linear bounce-averaged diffusion coefficients, is in agreement with the observed delay in the appearance of peak fluxes at SAMPEX in low Earth orbit. We also present techniques for modeling radiation belt dynamics using test particle trajectories in MHD fields. Simulations are performed using code developed by the Center for Integrated Space Weather Modeling.

Kress, B.; Hudson, M.; Looper, M.; Albert, J.; Lyon, J.; Goodrich, C.;

Published by: Journal of Geophysical Research      Published on: 09/2007

YEAR: 2007     DOI: 10.1029/2006JA012218

Shock-Induced Transport. Slot Refilling and Formation of New Belts.

Refilling of the slot region between the inner and outer electron radiation belts during geomagnetic storms

[1] Energetic electrons (>=50 keV) are injected into the slot region (2 < L < 4) between the inner and outer radiation belts during the early recovery phase of geomagnetic storms. Enhanced convection from the plasma sheet can account for the storm-time injection at lower energies but does not explain the rapid appearance of higher-energy electrons (>=150 keV). The effectiveness of either radial diffusion (driven by enhanced ULF waves) or local acceleration (during interactions with enhanced whistler mode chorus emissions), as a potential source for refilling the slot at higher energies, is analyzed for observed conditions during the early recovery phase of the 10 October 1990 storm. We demonstrate that local acceleration, driven by observed chorus emissions, can account for the rapid enhancement in 200\textendash700 keV electrons in the outer slot region near L = 3.3. Radial diffusion is much less effective but may partially contribute to the flux enhancement at lower L. Subsequent outward expansion of the plasmapause during the storm recovery phase effectively terminates local wave acceleration in the slot and prevents acceleration to energies higher than \~700 keV. A statistical analysis of energetic electron flux enhancements and wave and plasma properties over the entire CRRES mission supports the concept of local wave acceleration as a dominant process for refilling the slot during the main and early recovery phase of storms. For moderate storms, the injection process naturally becomes less effective at energies >=1 MeV, due to the longer wave acceleration times and additional precipitation loss from scattering by electromagnetic ion cyclotron waves. However, during extreme events when the plasmapause remains compressed for several days, conditions may occur to allow wave acceleration to multi-MeV energies at locations normally associated with the slot.

Thorne, R.; Shprits, Y; Meredith, N.; Horne, R.; Li, W.; Lyons, L.;

Published by: Journal of Geophysical Research      Published on: 06/2007

YEAR: 2007     DOI: 10.1029/2006JA012176

Shock-Induced Transport. Slot Refilling and Formation of New Belts.


An extreme distortion of the Van Allen belt arising from the \textquoteleftHallowe\textquoterighten\textquoteright solar storm in 2003

The Earth\textquoterights radiation belts\textemdashalso known as the Van Allen belts1\textemdashcontain high-energy electrons trapped on magnetic field lines2, 3. The centre of the outer belt is usually 20,000\textendash25,000 km from Earth. The region between the belts is normally devoid of particles2, 3, 4, and is accordingly favoured as a location for spacecraft operation because of the benign environment5. Here we report that the outer Van Allen belt was compressed dramatically by a solar storm known as the \textquoteleftHallowe\textquoterighten storm\textquoteright of 2003. From 1 to 10 November, the outer belt had its centre only ~10,000 km from Earth\textquoterights equatorial surface, and the plasmasphere was similarly displaced inwards. The region between the belts became the location of high particle radiation intensity. This remarkable deformation of the entire magnetosphere implies surprisingly powerful acceleration and loss processes deep within the magnetosphere.

Baker, D.; Kanekal, S.; Li, X.; Monk, S.; Goldstein, J.; Burch, J.;

Published by: Nature      Published on: 12/2004

YEAR: 2004     DOI: 10.1038/nature03116

Shock-Induced Transport. Slot Refilling and Formation of New Belts.


MHD/particle simulations of radiation belt dynamics

Particle fluxes in the outer radiation belts can show substantial variation in time, over scales ranging from a few minutes, such as during the sudden commencement phase of geomagnetic storms, to the years-long variations associated with the progression of the solar cycle. As the energetic particles comprising these belts can pose a hazard to human activity in space, considerable effort has gone into understanding both the source of these particles and the physics governing their dynamical behavior. Computationally tracking individual test particles in a model magnetosphere represents a very direct, physically-based approach to modeling storm-time radiation belt dynamics. Using global magnetohydrodynamic models of the Earth\textendashSun system coupled with test particle simulations of the radiation belts, we show through two examples that such simulations are capable of capturing the outer zone radiation belt configuration at a variety of time scales and through all phases of a geomagnetic storm. Such simulations provide a physically-based method of investigating the dynamics of the outer radiation zone, and hold promise as a viable method of providing global nowcasts of the radiation environment during geomagnetically active periods.

ELKINGTON, S; Hudson, M.; Wiltberger, M.J; Lyon, J.;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 04/2002

YEAR: 2002     DOI: 10.1016/S1364-6826(02)00018-4

Shock-Induced Transport. Slot Refilling and Formation of New Belts.


Large amplitude electric and magnetic field signatures in the inner magnetosphere during injection of 15 MeV electron drift echoes

Electric and magnetic fields were measured by the CRRES spacecraft at an L-value of 2.2 to 2.6 near 0300 magnetic local time during a strong storm sudden commencement (SSC) on March 24, 1991. The electric field signature at the spacecraft at the time of the SSC was characterized by a large amplitude oscillation (80 mV/m peak to peak) with a period corresponding to the 150 second drift echo period of the simultaneously observed 15 MeV electrons. Considerations of previous statistical studies of the magnitude of SSC electric and magnetic fields versus local time and analysis of the energization and cross-L transport of the particles imply the existence of 200 to 300 mV/m electric fields over much of the dayside magnetosphere. These observations also suggest that the 15 MeV drift echo electrons were selectively energized because their gradient drift velocity allowed them to reside in the region of strong electric fields for the duration of the accelerating phase of the electric field.

Wygant, J.; Mozer, F.; Temerin, M.; Blake, J.; Maynard, N.; Singer, H.; Smiddy, M.;

Published by: Geophysical Research Letters      Published on: 08/1994

YEAR: 1994     DOI: 10.1029/94GL00375

Shock-Induced Transport. Slot Refilling and Formation of New Belts.


Simulation of the prompt energization and transport of radiation belt particles during the March 24, 1991 SSC

We model the rapid (\~ 1 min) formation of a new electron radiation belt at L ≃ 2.5 that resulted from the Storm Sudden Commencement (SSC) of March 24, 1991 as observed by the CRRES satellite. Guided by the observed electric and magnetic fields, we represent the time-dependent magnetospheric electric field during the SSC by an asymmetric bipolar pulse that is associated with the compression and relaxation of the Earth\textquoterights magnetic field. We follow the electrons using a relativistic guiding center code. The test-particle simulations show that electrons with energies of a few MeV at L > 6 were energized up to 40 MeV and transported to L ≃ 2.5 during a fraction of their drift period. The energization process conserves the first adiabatic invariant and is enhanced due to resonance of the electron drift motion with the time-varying electric field. Our simulation results, with an initial W-8 energy flux spectra, reproduce the observed electron drift echoes and show that the interplanetary shock impacted the magnetosphere between 1500 and 1800 MLT.

Li, Xinlin; Roth, I.; Temerin, M.; Wygant, J.; Hudson, M.; Blake, J.;

Published by: Geophysical Research Letters      Published on: 11/1993

YEAR: 1993     DOI: 10.1029/93GL02701

Shock-Induced Transport. Slot Refilling and Formation of New Belts.