| 1. |
- Allen, R. C., et al.
(author)
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A statistical study of EMIC waves observed by Cluster : 1. Wave properties
- 2014
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In: 2014 XXXITH URSI General Assembly And Scientific Symposium (URSI GRASS). - 9781467352253
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Conference paper (peer-reviewed)abstract
- Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the L-MLT frame within a limited MLAT range. In this study, we present a statistical analysis of EMIC wave properties using ten years (2001-2010) of data from Cluster, totaling 17,987 minutes of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The current paper focuses on the wave occurrence distribution as well as the distribution of wave properties.
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| 2. |
- Allen, R. C., et al.
(author)
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A statistical study of EMIC waves observed by Cluster : 2. Associated plasma conditions
- 2016
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In: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:7, s. 6458-6479
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Journal article (peer-reviewed)abstract
- This is the second in a pair of papers discussing a statistical study of electromagnetic ion cyclotron (EMIC) waves detected during 10years (2001-2010) of Cluster observations. In the first paper, an analysis of EMIC wave properties (i.e., wave power, polarization, normal angle, and wave propagation angle) is presented in both the magnetic latitude (MLAT)-distance as well as magnetic local time (MLT)-L frames. This paper focuses on the distribution of EMIC wave-associated plasma conditions as well as two EMIC wave generation proxies (the electron plasma frequency to gyrofrequency ratio proxy and the linear theory proxy) in these same frames. Based on the distributions of hot H+ anisotropy, electron and hot H+ density measurements, hot H+ parallel plasma beta, and the calculated wave generation proxies, three source regions of EMIC waves appear to exist: (1) the well-known overlap between cold plasmaspheric or plume populations with hot anisotropic ring current populations in the postnoon to dusk MLT region; (2) regions all along the dayside magnetosphere at high L shells related to dayside magnetospheric compression and drift shell splitting; and (3) off-equator regions possibly associated with the Shabansky orbits in the dayside magnetosphere.
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| 3. |
- Allen, R. C., et al.
(author)
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A statistical study of EMIC waves observed by Cluster : 1. Wave properties
- 2015
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In: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:7, s. 5574-5592
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Journal article (peer-reviewed)abstract
- Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10years (2001-2010) of data from Cluster, totaling 25,431min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.
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| 4. |
- Allen, R. C., et al.
(author)
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Multiple bidirectional EMIC waves observed by Cluster at middle magnetic latitudes in the dayside magnetosphere
- 2013
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In: Journal of Geophysical Research: Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 118:10, s. 6266-6278
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Journal article (peer-reviewed)abstract
- It is well accepted that the propagation of electromagnetic ion cyclotron (EMIC) waves are bidirectional near their source regions and unidirectional when away from these regions. The generally believed source region for EMIC waves is around the magnetic equatorial plane. Here we describe a series of EMIC waves in the Pc1 (0.2-5 Hz) frequency band above the local He+ cyclotron frequency observed in situ by all four Cluster spacecraft on 9 April 2005 at midmagnetic latitudes (MLAT = similar to 33 degrees-49 degrees) with L = 10.7-11.5 on the dayside (MLT = 10.3-10.4). A Poynting vector spectrum shows that the wave packets consist of multiple groups of packets propagating bidirectionally, rather than unidirectionally, away from the equator, while the local plasma conditions indicate that the spacecraft are entering into a region sufficient for local wave excitation. One possible interpretation is that, while part of the observed waves are inside their source region, the others are either close enough to the source region, or mixed with the wave packets from multiple source regions at different latitudes.
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| 5. |
- Dong, X. C., et al.
(author)
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Observation of Nonuniform Energy Dissipation in the Electron Diffusion Region of Magnetopause Reconnection
- 2021
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:13
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Journal article (peer-reviewed)abstract
- We use Magnetospheric Multiscale (MMS) data to investigate the energy dissipation in a magnetopause reconnection electron diffusion region (EDR) event with moderate guide field. The four MMS spacecraft were separated by about 10 km so that comparative study among spacecraft within the EDR can be implemented. Similar magnetic field and electric current properties at each spacecraft indicate the formation of a quasi-homogeneous magnetic and current structure in the diffusion region. However, we find that the energy dissipations detected by each spacecraft are still different due to the temporal or spatial effect of the out-of-plane reconnection electric field (EM) within the dissipation region. Our study suggests that the nonuniform or unsteady energy dissipation in the reconnection EDR may be a universal process.
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| 6. |
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| 7. |
- Kiyani, K. H., et al.
(author)
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Global Scale-Invariant Dissipation in Collisionless Plasma Turbulence
- 2009
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 103:7, s. 075006-
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Journal article (peer-reviewed)abstract
- A higher-order multiscale analysis of the dissipation range of collisionless plasma turbulence is presented using in situ high-frequency magnetic field measurements from the Cluster spacecraft in a stationary interval of fast ambient solar wind. The observations, spanning five decades in temporal scales, show a crossover from multifractal intermittent turbulence in the inertial range to non-Gaussian mono-scaling in the dissipation range. This presents a strong observational constraint on theories of dissipation mechanisms in turbulent collisionless plasmas.
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| 8. |
- Li, B., et al.
(author)
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Magnetospheric Multiscale Observations of ULF Waves and Correlated Low-Energy Ion Monoenergetic Acceleration
- 2019
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In: Journal of Geophysical Research - Space Physics. - : Blackwell Publishing Ltd. - 2169-9380 .- 2169-9402.
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Journal article (peer-reviewed)abstract
- Low-energy ions of ionospheric origin with energies below 10s of electron volt dominate most of the volume and mass of the terrestrial magnetosphere. However, sunlit spacecraft often become positively charged to several 10s of volts, which prevents low-energy ions from reaching the particle detectors on the spacecraft. Magnetospheric Multiscale spacecraft (MMS) observations show that ultralow-frequency (ULF) waves drive low-energy ions to drift in the E × B direction with a drift velocity equal to V E × B , and low-energy ions were accelerated to sufficient total energy to be measured by the MMS/Fast Plasma Investigation Dual Ion Spectrometers. The maximum low-energy ion energy flux peak seen in MMS1's dual ion spectrometer measurements agreed well with the theoretical calculation of H + ion E × B drift energy. The density of ions in the energy range below minimum energy threshold was between 1 and 3 cm −3 in the magnetosphere subsolar region in this event.
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| 9. |
- Lui, A. T. Y., et al.
(author)
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Breakdown of the frozen-in condition in the Earth's magnetotail
- 2007
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112:A4, s. A04215-
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Journal article (peer-reviewed)abstract
- [1] We investigate in detail the breakdown of the frozen-in condition detected by Cluster at the downstream distance of similar to 19 R-E in the midnight sector of the magnetotail during a substorm expansion on 22 August 2001. It is found that the breakdown occurred ( 1) in a low-density environment with moderate to large proton plasma flow and significant fluctuations in electric and magnetic fields, ( 2) in regions with predominantly dissipation but occasionally dynamo effect, and ( 3) at times simultaneously at two Cluster satellites separated by more than 1000 km in both X- and Z-directions. Evaluation of the terms in the generalized Ohm's law indicates that the anomalous resistivity contribution arising from field fluctuations during this event is the most significant, followed by the Hall, electron viscosity, and inertial contributions in descending order of importance. This result demonstrates for the first time from observations that anomalous resistivity from field fluctuations ( implying kinetic instabilities) can play a substantial role in the breakdown of the frozen-in condition in the magnetotail during substorm expansions. Consideration of several observed features in the breakdown regions indicates that the breakdown occurs in a turbulent site resembling observed features found in current disruption and dipolarization sites.
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| 10. |
- Lui, A. T. Y., et al.
(author)
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Cluster observation of plasma flow reversal in the magnetotail during a substorm
- 2006
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In: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 24:7, s. 2005-2013
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Journal article (peer-reviewed)abstract
- We investigate in detail a reversal of plasma flow from tailward to earthward detected by Cluster at the downstream distance of similar to 19 RE in the midnight sector of the magnetotail on 22 August 2001. This flow reversal was accompanied by a sign reversal of the B-z component and occurred during the late substorm expansion phase as revealed by simultaneous global view of auroral activity from IMAGE. We examine the associated Hall current system signature, current density, electric field, Lorentz force, and current dissipation/dynamo term, the last two parameters being new features that have not been studied previously for plasma flow reversals. It is found that (1) there was no clear quadrupole Hall current system signature organized by the flow reversal time, (2) the x-component of the Lorentz force did not change sign while the other two did, (3) the timing sequence of flow reversal from the Cluster configuration did not match tailward motion of a single plasma flow source, (4) the electric field was occasionally dawnward, producing a dynamo effect, and (5) the electric field was occasionally larger at the high-latitude plasma sheet than near the neutral sheet. These observations are consistent with the current disruption model for substorms in which these disturbances are due to shifting dominance of multiple current disruption sites and turbulence at the observing location.
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