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Authors: UKHORSKIY A, and SITNOV M
Title: Radial transport in the outer radiation belt due to global magnetospheric compressions
Abstract: Earth's outer radiation belt is populated by relativistic electrons that produce a complex dynamical response to varying geomagnetic activity. One fundamental process defining global state of the belt is radial transport of electrons across their drift shells. Radial transport is induced by resonant interaction of electron drift motion with ULF oscillations of electric and magnetic fields and is commonly believed to be a diffusive process. The goal of this paper is the analysis of radial transport due to typical ULF fluctuations in the inner magnetospheric fields. For this purpose a test-particle approach is used in the guiding center approximation. In particular we consider ULF oscillations due to global magnetospheric compressions. It is shown that typical pressure variations induce larg. . .
Date: 11/2008 Publisher: Journal of Atmospheric and Solar-Terrestrial Physics Pages: 1714 - 1726 DOI: 10.1016/j.jastp.2008.07.018 Available at: http://www.sciencedirect.com/science/article/pii/S1364682608001971
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Authors: Ukhorskiy A Y, Sitnov M I, Merkin V. G., and Artemyev A. V.
Title: Rapid acceleration of protons upstream of earthward propagating dipolarization fronts
Abstract: [1] Transport and acceleration of ions in the magnetotail largely occurs in the form of discrete impulsive events associated with a steep increase of the tail magnetic field normal to the neutral plane (Bz), which are referred to as dipolarization fronts. The goal of this paper is to investigate how protons initially located upstream of earthward moving fronts are accelerated at their encounter. According to our analytical analysis and simplified two-dimensional test-particle simulations of equatorially mirroring particles, there are two regimes of proton acceleration: trapping and quasi-trapping, which are realized depending on whether the front is preceded by a negative depletion in Bz. We then use three-dimensional test-particle simulations to investigate how these acceleration processe. . .
Date: 01/2013 Publisher: Journal of Geophysical Research: Space Physics Pages: 4952–4962, DOI: 10.1002/jgra.50452 Available at: http://doi.wiley.com/10.1002/jgra.50452
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Authors: Ukhorskiy Aleksandr Y., Mauk Barry H., Fox Nicola J., Sibeck David G., and Grebowsky Joseph M.
Title: Radiation belt storm probes: Resolving fundamental physics with practical consequences
Abstract: The fundamental processes that energize, transport, and cause the loss of charged particles operate throughout the universe at locations as diverse as magnetized planets, the solar wind, our Sun, and other stars. The same processes operate within our immediate environment, the Earth's radiation belts. The Radiation Belt Storm Probes (RBSP) mission will provide coordinated two-spacecraft observations to obtain understanding of these fundamental processes controlling the dynamic variability of the near-Earth radiation environment. In this paper we discuss some of the profound mysteries of the radiation belt physics that will be addressed by RBSP and briefly describe the mission and its goals.
Date: 07/2011 Publisher: Journal of Atmospheric and Solar-Terrestrial Physics Pages: 1417 - 1424 DOI: 10.1016/j.jastp.2010.12.005 Available at: http://www.sciencedirect.com/science/article/pii/S1364682610003688
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Authors: Ukhorskiy A Y, and Sitnov M I
Title: Dynamics of Radiation Belt Particles
Abstract: This paper reviews basic concepts of particle dynamics underlying theoretical aspect of radiation belt modeling and data analysis. We outline the theory of adiabatic invariants of quasiperiodic Hamiltonian systems and derive the invariants of particle motion trapped in the radiation belts. We discuss how the nonlinearity of resonant interaction of particles with small-amplitude plasma waves, ubiquitous across the inner magnetosphere, can make particle motion stochastic. Long-term evolution of a stochastic system can be described by the Fokker-Plank (diffusion) equation. We derive the kinetic equation of particle diffusion in the invariant space and discuss its limitations and associated challenges which need to be addressed in forthcoming radiation belt models and data analysis.
Date: 11/2013 Publisher: Space Science Reviews Pages: 545-578 DOI: 10.1007/s11214-012-9938-5 Available at: http://link.springer.com/article/10.1007%2Fs11214-012-9938-5
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Authors: Ukhorskiy A Y, Sorathia K. A., Merkin V. G., Sitnov M I, Mitchell D G, et al.
Title: Ion Trapping and Acceleration at Dipolarization Fronts: High-Resolution MHD/Test-Particle Simulations
Abstract: Much of plasma heating and transport from the magnetotail into the inner magnetosphere occurs in the form of mesoscale discrete injections associated with sharp dipolarizations of magnetic field (dipolarization fronts). In this paper we investigate the role of magnetic trapping in acceleration and transport of the plasmasheet ions into the ring current. For this purpose we use high‐resolution global MHD and three‐dimensional test‐particle simulations. It is shown that trapping, produced by sharp magnetic field gradients at the interface between dipolarizations and the ambient plasma, affect plasmasheet protons with energies above approximately 10 keV, enabling their transport across more than 10 Earth radii and acceleration by a factor of 10. Our estimates show that trapping is impor. . .
Date: 06/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025370 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025370
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Authors: Ukhorskiy A Y, Sitnov M I, Millan R M, Kress B T, Fennell J. F., et al.
Title: Global Storm-Time Depletion of the Outer Electron Belt
Abstract: The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by ordersof magnitude at different spatial and temporal scale. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main-phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause . . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020645 Available at: http://doi.wiley.com/10.1002/2014JA020645
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Authors: Ukhorskiy A Y, Takahashi K, Anderson B. J., and Korth H.
Title: Impact of toroidal ULF waves on the outer radiation belt electrons
Abstract: Relativistic electron fluxes in the outer radiation belt exhibit highly variable complex behavior. Previous studies have established a strong correlation of electron fluxes and the inner magnetospheric ULF waves in the Pc 3–5 frequency range. Resonant interaction of ULF waves with the drift motion of radiation belt electrons violates their third adiabatic invariant and consequently leads to their radial transport. If the wave-particle interaction has a stochastic character, then the electron transport is diffusive. The goal of this paper is to analyze the impact of toroidal ULF waves on radiation belt electrons. The study is based on direct measurements of ULF electric fields on the CRRES spacecraft. We show that the electric fields of inner magnetospheric toroidal ULF waves exhibit high. . .
Date: 10/2005 Publisher: Journal of Geophysical Research DOI: 10.1029/2005JA011017 Available at: http://onlinelibrary.wiley.com/doi/10.1029/2005JA011017/abstract
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Authors: Ukhorskiy A Y, Sitnov M I, Merkin V. G., Gkioulidou M., and Mitchell D G
Title: Ion acceleration at dipolarization fronts in the inner magnetosphere
Abstract: During geomagnetic storms plasma pressure in the inner magnetosphere is controlled by energetic ions of tens to hundreds of keV. Plasma pressure is the source of global storm time currents, which control the distribution of magnetic field and couple the inner magnetosphere and the ionosphere. Recent analysis showed that the buildup of hot ion population in the inner magnetosphere largely occurs in the form of localized discrete injections associated with sharp dipolarizations of magnetic field, similar to dipolarization fronts in the magnetotail. Because of significant differences between the ambient magnetic field and the dipolarization front properties in the magnetotail and the inner magnetosphere, the physical mechanisms of ion acceleration at dipolarization fronts in these two regions. . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023304 Available at: http://doi.wiley.com/10.1002/2016JA023304
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Authors: Ukhorskiy A Y, Sitnov M I, Mitchell D G, Takahashi K, Lanzerotti L J, et al.
Title: Rotationally driven ‘zebra stripes’ in Earth’s inner radiation belt
Abstract: Structured features on top of nominally smooth distributions of radiation-belt particles at Earth have been previously associated with particle acceleration and transport mechanisms powered exclusively by enhanced solar-wind activity1, 2, 3, 4. Although planetary rotation is considered to be important for particle acceleration at Jupiter and Saturn5, 6, 7, 8, 9, the electric field produced in the inner magnetosphere by Earth’s rotation can change the velocity of trapped particles by only about 1–2 kilometres per second, so rotation has been thought inconsequential for radiation-belt electrons with velocities of about 100,000 kilometres per second. Here we report that the distributions of energetic electrons across the entire spatial extent of Earth’s inner radiation belt are organize. . .
Date: 01/2014 Publisher: Nature Pages: 338 - 340 DOI: 10.1038/nature13046 Available at: http://www.nature.com/doifinder/10.1038/nature13046
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Authors: Ukhorskiy A Y, Anderson B J, Brandt P C, and Tsyganenko N A
Title: Storm time evolution of the outer radiation belt: Transport and losses
Abstract: During geomagnetic storms the magnetic field of the inner magnetosphere exhibits large-scale variations over timescales from minutes to days. Being mainly controlled by the magnetic field the motion of relativistic electrons of the outer radiation belt can be highly susceptible to its variations. This paper investigates evolution of the outer belt during the 7 September 2002 storm. Evolution of electron phase space density is calculated with the use of a test-particle simulation in storm time magnetic and electric fields. The results show that storm time intensification of the ring current produces a large impact on the belt. In contrast to the conventional Dst effect the dominant effects are nonadiabatic and lead to profound and irreversible transformations of the belt. The diamagnetic in. . .
Date: 11/2006 Publisher: Journal of Geophysical Research DOI: 10.1029/2006JA011690 Available at: http://onlinelibrary.wiley.com/doi/10.1029/2006JA011690/abstract
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Authors: Ukhorskiy A. Y., Sitnov M. I., Merkin V. G., Gkioulidou M., and Mitchell D. G.
Title: Acceleration at Dipolarization Fronts in the Inner Magnetosphere
Abstract: During geomagnetic storms plasma pressure in the inner magnetosphere is controlled by energetic ions of tens to hundreds keV. Plasma pressure is the source of global storm-time currents, which control the distribution of magnetic field and couple the inner magnetosphere and the ionosphere. Recent analysis showed that the buildup of hot ion population in the inner magnetosphere largely occurs in the form of localized discrete injections associated with sharp dipolarizations of magnetic field, similar to dipolarization fronts in the magnetotail. Because of significant differences between the ambient magnetic field and the dipolarization front properties in the magnetotail and the inner magnetosphere, the physical mechanisms of ion acceleration at dipolarization fronts in these two regions ma. . .
Date: 01/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016ja023304 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023304
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Authors: Usanova M. E., Malaspina D. M., Jaynes A. N., Bruder R. J., Mann I. R., et al.
Title: Van Allen Probes observations of oxygen cyclotron harmonic waves in the inner magnetosphere
Abstract: Waves with frequencies in the vicinity of the oxygen cyclotron frequency and its harmonics have been regularly observed on the Van Allen Probes satellites during geomagnetic storms. We focus on properties of these waves and present events from the main phase of two storms on 1 November 2012 and 17 March 2013 and associated dropouts of a few MeV electron fluxes. They are electromagnetic, in the frequency range ~0.5 to several Hz, and amplitude ~0.1 to a few nT in magnetic and ~0.1 to a few mV/m in electric field, with both the wave velocity and the Poynting vector directed almost parallel to the background magnetic field. These properties are very similar to those of electromagnetic ion cyclotron waves, which are believed to contribute to loss of ring current ions and radiation belt electro. . .
Date: 09/2016 Publisher: Geophysical Research Letters Pages: 8827 - 8834 DOI: 10.1002/grl.v43.1710.1002/2016GL070233 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL070233/abstract
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Authors: Usanova M. E., Drozdov A., Orlova K., Mann I. R., Shprits Y., et al.
Title: Effect of EMIC waves on relativistic and ultrarelativistic electron populations: Ground-based and Van Allen Probes observations
Abstract: We study the effect of electromagnetic ion cyclotron (EMIC) waves on the loss and pitch angle scattering of relativistic and ultrarelativistic electrons during the recovery phase of a moderate geomagnetic storm on 11 October 2012. The EMIC wave activity was observed in situ on the Van Allen Probes and conjugately on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity throughout an extended 18 h interval. However, neither enhanced precipitation of >0.7 MeV electrons nor reductions in Van Allen Probe 90° pitch angle ultrarelativistic electron flux were observed. Computed radiation belt electron pitch angle diffusion rates demonstrate that rapid pitch angle diffusion is confined to low pitch angles and cannot reach 90°. For the first time, from both obse. . .
Date: 03/2014 Publisher: Geophysical Research Letters Pages: 1375 - 1381 DOI: 10.1002/2013GL059024 Available at: http://doi.wiley.com/10.1002/2013GL059024
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