Biblio

Found 15 results
Filters: Author is Min, Kyungguk  [Clear All Filters]
2018
Authors: Boardsen Scott A., Hospodarsky George B., Min Kyungguk, Averkamp Terrance F., Bounds Scott R., et al.
Title: Determining the wave vector direction of equatorial fast magnetosonic waves
Abstract: We perform polarization analysis of the equatorial fast magnetosonic waves electric field over a 20 minute interval of Van Allen Probes A Waveform Receiver burst mode data. The wave power peaks at harmonics of the proton cyclotron frequency indicating the spacecraft is near or in the source region. The wave vector is inferred from the direction of the major axis of the electric field polarization ellipsoid and the sign of the phase between the longitudinal electric and compressional magnetic field components. We show that wave vector is preferentially in the azimuthal direction as opposed to the radial direction. From Poynting flux analysis one would infer that the wave vector is primarily in the radial direction. We show that the error in the Poynting flux is large ~ 90°. These results s. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL078695 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078695
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Authors: Min Kyungguk, Boardsen Scott A., Denton Richard E, and Liu Kaijun
Title: Equatorial Evolution of the Fast Magnetosonic Mode in the Source Region: Observation-Simulation Comparison of the Preferential Propagation Direction
Abstract: Recent analysis of an event observed by the Van Allen Probes in the source region outside the plasmapause has shown that fast magnetosonic waves (also referred to as equatorial noise) propagate preferentially in the azimuthal direction, implying that wave amplification should occur during azimuthal propagation. To demonstrate this, we carry out 2‐D particle‐in‐cell simulations of the fast magnetosonic mode at the dipole magnetic equator with the simulation box size, the magnetic field inhomogeneity, and the plasma parameters chosen from the same event recently analyzed. The self‐consistently evolving electric and magnetic field fluctuations are characterized by spectral peaks at harmonics of the local proton cyclotron frequency. The azimuthal component of the electric field fluctua. . .
Date: 11/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA026037 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA026037
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Authors: Min Kyungguk, Liu Kaijun, Wang Xueyi, Chen Lunjin, and Denton Richard E
Title: Fast Magnetosonic Waves Observed by Van Allen Probes: Testing Local Wave Excitation Mechanism
Abstract: Linear Vlasov theory and particle-in-cell (PIC) simulations for electromagnetic fluctuations in a homogeneous, magnetized, and collisionless plasma are used to investigate a fast magnetosonic wave event observed by the Van Allen Probes. The fluctuating magnetic field observed exhibits a series of spectral peaks at harmonics of the proton cyclotron frequency Ωp and has a dominant compressional component, which can be classified as fast magnetosonic waves. Furthermore, the simultaneously observed proton phase space density exhibits positive slopes in the perpendicular velocity space, ∂fp/∂v⊥>0, which can be a source for these waves. Linear theory analyses and PIC simulations use plasma and field parameters measured in situ except that the modeled proton distribution is modified to hav. . .
Date: 01/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024867 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024867/full
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Authors: Gamayunov Konstantin V., Min Kyungguk, Saikin Anthony A., and Rassoul Hamid
Title: Generation of EMIC Waves Observed by Van Allen Probes at Low L Shells
Abstract: Observation of linearly polarized He+‐band electromagnetic ion cyclotron (EMIC) waves at low L shells is a new, and quite unexpected, result from the Van Allen Probes mission. Here we analyze the two EMIC wave events observed by Van Allen Probes at low L shells and put forward a new‐generation mechanism for the low‐L EMIC waves. Both events were observed at L ∼ 3 but one of them has a discrete spectrum near the O+ gyrofrequency and its second harmonic, whereas the second event has a broad spectrum between the O+ gyrofrequency and its second harmonic. For both events, the major conclusions of our analysis can be summarized as follows. (1) Only O+ causes EMIC wave generation, and instability is driven by the positive derivatives of distribution functions over perpendicular component . . .
Date: 10/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025629 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025629
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Authors: Takahashi Kazue, Oimatsu Satoshi, é Masahito, Min Kyungguk, Claudepierre Seth G., et al.
Title: Van Allen Probes Observations of Second Harmonic Poloidal Standing Alfvén Waves
Abstract: Long-lasting second-harmonic poloidal standing Alfvén waves (P2 waves) were observed by the twin Van Allen Probes (Radiation Belt Storm Probes, or RBSP) spacecraft in the noon sector of the plasmasphere, when the spacecraft were close to the magnetic equator and had a small azimuthal separation. Oscillations of proton fluxes at the wave frequency (∼10 mHz) were also observed in the energy (W) range 50–300 keV. Using the unique RBSP orbital configuration, we determined the phase delay of magnetic field perturbations between the spacecraft with a 2nπ ambiguity. We then used finite gyroradius effects seen in the proton flux oscillations to remove the ambiguity and found that the waves were propagating westward with an azimuthal wave number (m) of ∼−200. The phase of the proton flux . . .
Date: 01/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024869 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024869/full
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2017
Authors: Min Kyungguk, Denton Richard E, Liu Kaijun, Gary Peter, and Spence Harlan E.
Title: Ion Bernstein instability as a possible source for oxygen ion cyclotron harmonic waves
Abstract: This paper demonstrates that an ion Bernstein instability can be a possible source for recently reported electromagnetic waves with frequencies at or near the singly ionized oxygen ion cyclotron frequency, inline image, and its harmonics. The particle measurements during strong wave activity revealed a relatively high concentration of oxygen ions (∼15%) whose phase space density exhibits a local peak at energy ∼20 keV. Given that the electron plasma-to-cyclotron frequency ratio is inline image, this energy corresponds to the particle speed inline image, where vA is the oxygen Alfvén speed. Using the observational key plasma parameters, a simplified ion velocity distribution is constructed, where the local peak in the oxygen ion velocity distribution is represented by an isotropic s. . .
Date: 05/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA023979 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA023979/full
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Authors: Min Kyungguk, Takahashi Kazue, Ukhorskiy Aleksandr Y., Manweiler Jerry W., Spence Harlan E., et al.
Title: Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector
Abstract: This paper presents observations of ultralow-frequency (ULF) waves from Van Allen Probes. The event that generated the ULF waves occurred 2 days after a minor geomagnetic storm during a geomagnetically quiet time. Narrowband pulsations with a frequency of about 7 mHz with moderate amplitudes were registered in the premidnight sector when Probe A was passing through an enhanced density region near geosynchronous orbit. Probe B, which passed through the region earlier, did not detect the narrowband pulsations but only broadband noise. Despite the single-spacecraft measurements, we were able to determine various wave properties. We find that (1) the observed waves are a second harmonic poloidal mode propagating westward with an azimuthal wave number estimated to be ∼100; (2) the magnetic fi. . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics Pages: 3013-3-39 DOI: 10.1002/2016JA023770 Available at: onlinelibrary.wiley.com/doi/10.1002/2016JA023770/full
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2015
Authors: Min Kyungguk, Liu Kaijun, Bonnell John W., Breneman Aaron W., Denton Richard E, et al.
Title: Study of EMIC wave excitation using direct ion measurements
Abstract: With data from Van Allen Probes, we investigate EMIC wave excitation using simultaneously observed ion distributions. Strong He-band waves occurred while the spacecraft was moving through an enhanced density region. We extract from Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer measurement the velocity distributions of warm heavy ions as well as anisotropic energetic protons that drive wave growth through the ion cyclotron instability. Fitting the measured ion fluxes to multiple sinm-type distribution functions, we find that the observed ions make up about 15% of the total ions, but about 85% of them are still missing. By making legitimate estimates of the unseen cold (below ~2 eV) ion composition from cutoff frequencies suggested by the observed wave spectrum, a series of. . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020717 Available at: http://doi.wiley.com/10.1002/2014JA020717
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2014
Authors: Takahashi Kazue, Denton Richard E, Kurth William, Kletzing Craig, Wygant John, et al.
Title: Externally driven plasmaspheric ULF waves observed by the Van Allen Probes
Abstract: We analyze data acquired by the Van Allen Probes on 8 November 2012, during a period of extended low geomagnetic activity, to gain new insight into plasmaspheric ultra-low-frequency (ULF) waves. The waves exhibited strong spectral power in the 5–40 mHzband and included multiharmonic toroidal waves visible up to the 11th harmonic, unprecedented in the plasmasphere. During this wave activity, the interplanetary magnetic field cone angle was small, suggesting that the waves were driven by broadband compressional ULF waves originating in the foreshock region. This source mechanism is supported by the tailward propagation of the compressional magnetic field perturbations at a phase velocity of a few hundred kilometers per second that is determined bythe cross phase analysis of data from the t. . .
Date: 12/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020373 Available at: http://doi.wiley.com/10.1002/2014JA020373
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Authors: Fu Xiangrong, Cowee Misa M., Friedel Reinhard H., Funsten Herbert O, Gary Peter, et al.
Title: Whistler Anisotropy Instabilities as the Source of Banded Chorus: Van Allen Probes Observations and Particle-in-Cell Simulations
Abstract: Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr < Ωe, where Ωe is the electron cyclotron frequency, and a characteristic spectral gap at ωr ≃ Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell (PIC) simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from HOPE instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron mod. . .
Date: 10/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020364 Available at: http://doi.wiley.com/10.1002/2014JA020364
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2013
Authors: Lee Jeongwoo, Min Kyungguk, and Kim Kap-Sung
Title: Characteristic dimension of electromagnetic ion cyclotron wave activity in the magnetosphere
Abstract: [1] In this paper, we estimate the size of coherent activity of electromagnetic ion cyclotron (EMIC) waves using the multi‒spacecraft observations made during the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. We calculate the cross‒correlations between EMIC wave powers measured by different THEMIS spacecraft, plot them over the separation distances between pairs of observing spacecraft, and determine the 1/e folding distance of the correlations as the characteristic dimension of the coherent wave activity. The characteristic radius in the direction transverse to the local magnetic field is found to lie in rather a wide range of 1500–8600 km varying from the AM to PM sectors and also from hydrogen to helium bands. However, the characteristic d. . .
Date: 04/2013 Publisher: Journal of Geophysical Research: Space Physics Pages: 1651 - 1658 DOI: 10.1002/jgra.50242 Available at: http://doi.wiley.com/10.1002/jgra.50242
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Authors: Min Kyungguk, Bortnik J, and Lee Jeongwoo
Title: A novel technique for rapid L* calculation using UBK coordinates
Abstract: [1] The magnetic drift invariant (L*) is an important quantity used for tracking and organizing particle dynamics in the radiation belts, but its accurate calculation has been computationally expensive in the past, thus making it difficult to employ this quantity in real-time space weather applications. In this paper, we propose a new, efficient method to calculate L* using the principle of energy conservation. This method uses Whipple's (U, B, K) coordinates to quickly and accurately determine trajectories of particles at the magnetic mirror point from two-dimensional isoenergy contours. The method works for any magnetic field configuration and is able to accommodate constant electric potential along field lines. We compare the result of this method with those of International Radiation B. . .
Date: 01/2013 Publisher: Journal of Geophysical Research DOI: 10.1029/2012JA018177
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Authors: Min Kyungguk, Bortnik J, and Lee Jeongwoo
Title: A novel technique for rapid L∗ calculation: algorithm and implementation
Abstract: Computing the magnetic drift invariant, L*, rapidly and accurately has always been a challenge to magnetospheric modelers, especially given the im- portance of this quantity in the radiation belt community. Min et al. (2013) proposed a new method of calculating L* using the principle of energy con- servation. Continuing with the approach outlined therein, the present pa- per focuses on the technical details of the algorithm to outline the implemen- tation, systematic analysis of accuracy, and verification of the speed of the new method. We also show new improvements which enable near real-time computation of L*. The relative error is on the order of 10−3 when ∼ 0.1 RE grid resolution is used and the calculation speed is about two seconds per particle in the popular Tsyganenko. . .
Date: 05/2013 Publisher: Journal of Geophysical Research Pages: 1912-1921 DOI: 10.1002/jgra.50250 Available at: http://onlinelibrary.wiley.com/doi/10.1002/jgra.50250/full
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2012
Authors: Min Kyungguk, Lee Jeongwoo, Keika Kunihiro, and Li W
Title: Global distribution of EMIC waves derived from THEMIS observations
Abstract: [1] Electromagnetic ion cyclotron (EMIC) waves play an important role in magnetospheric dynamics and their global distribution has been of great interest. This paper presents the distribution of EMIC waves over a broader range than ever before, as enabled by observations with the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft from 2007 to 2010. Our major findings are: (1) There are two major peaks in the EMIC wave occurrence probability. One is at dusk and 8–12 RE where the helium band dominates the hydrogen band waves. The other is at dawn and 10–12 RE where the hydrogen band dominates the helium band waves. (2) In terms of wave spectral power the dusk events are stronger (≈10 nT2/Hz) than the dawn events (≈3 nT2/Hz). (3) The dawn . . .
Date: 05/2012 Publisher: Journal of Geophysical Research DOI: 10.1029/2012JA017515
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2010
Authors: Min Kyungguk, Lee Jeongwoo, and Keika Kunihiro
Title: Chorus wave generation near the dawnside magnetopause due to drift shell splitting of substorm-injected electrons
Abstract: We study the relationship between the electron injection and the chorus waves during a substorm event on 23 March 2007. The chorus waves were detected at high geomagnetic latitude (∼70°S) Antarctic observatories in the range of 0600–0900 h in magnetic local time (MLT). Electrons drifting from the injection event were measured by two LANL spacecraft at 0300 and 0900 MLT. The mapping of auroral brightening areas to the magnetic equator shows that the injection occurred in an MLT range of 2200–2400. This estimate is consistent with observations by the THEMIS A, B, and D spacecraft (which were located at 2100 MLT and did not observe electron injections). Our backward model tracing from the magnetic equator near the dawnside magnetopause (which magnetically connects to the Antar. . .
Date: 10/2010 Publisher: American Geophysical Union DOI: 10.1029/2010JA015474
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