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Found 1197 entries in the Bibliography.
Showing entries from 601 through 650
| 2017 |
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Based on the Van Allen Probe A observations from 1 October 2012 to 31 December 2014, we develop two empirical models to respectively describe the hiss wave normal angle (WNA) and amplitude variations in the Earth\textquoterights plasmasphere for different substorm activities. The long-term observations indicate that the plasmaspheric hiss amplitudes on the dayside increase when substorm activity is enhanced (AE index increases), and the dayside hiss amplitudes are greater than the nightside. However, the propagation angles (WNAs) of hiss waves in most regions do not depend strongly on substorm activity, except for the intense substorm-induced increase in WNAs in the nightside low L-region. The propagation angles of plasmaspheric hiss increase with increasing magnetic latitude or decreasing radial distance (L-value). The global hiss WNAs (the power-weighted averages in each grid) and amplitudes (medians) can be well reproduced by our empirical models. Yu, J.; Li, L; Cao, J.; Chen, L.; Wang, J.; Yang, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023372 hiss amplitude model; hiss wave amplitude; Plasmaspheric Hiss; propagation angle model of hiss waves; substorm dependence; Van Allen Probes; wave normal angle |
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Based on the Van Allen Probe A observations from 1 October 2012 to 31 December 2014, we develop two empirical models to respectively describe the hiss wave normal angle (WNA) and amplitude variations in the Earth\textquoterights plasmasphere for different substorm activities. The long-term observations indicate that the plasmaspheric hiss amplitudes on the dayside increase when substorm activity is enhanced (AE index increases), and the dayside hiss amplitudes are greater than the nightside. However, the propagation angles (WNAs) of hiss waves in most regions do not depend strongly on substorm activity, except for the intense substorm-induced increase in WNAs in the nightside low L-region. The propagation angles of plasmaspheric hiss increase with increasing magnetic latitude or decreasing radial distance (L-value). The global hiss WNAs (the power-weighted averages in each grid) and amplitudes (medians) can be well reproduced by our empirical models. Yu, J.; Li, L; Cao, J.; Chen, L.; Wang, J.; Yang, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023372 hiss amplitude model; hiss wave amplitude; Plasmaspheric Hiss; propagation angle model of hiss waves; substorm dependence; Van Allen Probes; wave normal angle |
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Using the Van Allen Probe long-term (2013 \textendash 2015) observations and quasi-linear simulations of wave-particle interactions, we examine the combined or competing effects of whistler-mode waves (chorus or hiss) and magnetosonic (MS) waves on energetic (<0.5 MeV) and relativistic (>0.5 MeV) electrons inside and outside the plasmasphere. Although whistler-mode chorus waves and MS waves can singly or jointly accelerate electrons from the hundreds of keV energy to the MeV energy in the low-density trough, most of the relativistic electron enhancement events are best correlated with the chorus wave emissions outside the plasmapause. Inside the plasmasphere, intense plasmaspheric hiss can cause the net loss of relativistic electrons via persistent pitch angle scattering, regardless of whether MS waves were present or not. The intense hiss waves not only create the energy-dependent electron slot region, but also remove a lot of the outer radiation belt electrons when the expanding dayside plasmasphere frequently covers the outer zone. Since whistler-mode waves (chorus or hiss) can resonate with more electrons than MS waves, they play dominant roles in changing the outer radiation belt and the slot region. However, MS waves can accelerate the energetic electrons below 400 keV and weaken their loss inside the plasmapause. Thus, MS waves and plasmaspheric hiss generate different competing effects on energetic and relativistic electrons in the high-density plasmasphere. Li, L; Yu, J.; Cao, J.; Yang, J; Li, X.; Baker, D.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023634 magnetosonic waves; Plasmapause movement; Spatial variation of outer radiaton belt; Spatial variation of slot region; Temporal-spatial variations of chorus waves; Temporal-spatial variations of plasmaspheric hiss; Van Allen Probes |
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Spatial Scale and Duration of One Microburst Region on 13 August 2015 Prior studies of microburst precipitation have largely relied on estimates of the spatial scale and temporal duration of the microburst region in order to determine the radiation belt loss rate of relativistic electrons. These estimates have often relied on the statistical distribution of microburst events. However, few studies have directly observed the spatial and temporal evolution of a single microburst event. In this study, we combine BARREL balloon-borne X-ray measurements with FIREBIRD-II and AeroCube-6 CubeSat electron measurements to determine the spatial and temporal evolution of a microburst region in the morning MLT sector on 13 August 2015. The microburst region is found to extend across at least four hours in local time in the morning sector, from 09:00 to 13:00 MLT, and from L of 5 out to 10. The microburst event lasts for nearly nine hours. Smaller scale structure is investigated using the dual AeroCube-6 CubeSats, and is found to be consistent with the spatial size of whistler mode chorus wave observations near the equatorial plane. Anderson, B.; Shekhar, S.; Millan, R.; Crew, A.; Spence, H.; Klumpar, D.; Blake, J.; O\textquoterightBrien, T.; Turner, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023752 Microbursts; Radiation Belt Dynamics; Van Allen Probes; whistler mode chorus waves |
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Spatial Scale and Duration of One Microburst Region on 13 August 2015 Prior studies of microburst precipitation have largely relied on estimates of the spatial scale and temporal duration of the microburst region in order to determine the radiation belt loss rate of relativistic electrons. These estimates have often relied on the statistical distribution of microburst events. However, few studies have directly observed the spatial and temporal evolution of a single microburst event. In this study, we combine BARREL balloon-borne X-ray measurements with FIREBIRD-II and AeroCube-6 CubeSat electron measurements to determine the spatial and temporal evolution of a microburst region in the morning MLT sector on 13 August 2015. The microburst region is found to extend across at least four hours in local time in the morning sector, from 09:00 to 13:00 MLT, and from L of 5 out to 10. The microburst event lasts for nearly nine hours. Smaller scale structure is investigated using the dual AeroCube-6 CubeSats, and is found to be consistent with the spatial size of whistler mode chorus wave observations near the equatorial plane. Anderson, B.; Shekhar, S.; Millan, R.; Crew, A.; Spence, H.; Klumpar, D.; Blake, J.; O\textquoterightBrien, T.; Turner, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023752 Microbursts; Radiation Belt Dynamics; Van Allen Probes; whistler mode chorus waves |
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Variations of the relativistic electron flux after a magnetospheric compression event On January 21, 2015, a sharp increase of the solar wind dynamic pressure impacted the magnetosphere. The magnetopause moved inward to the region L< 8 without causing a geomagnetic storm. The flux of the relativistic electrons in the outer radiation belt decreased by half during this event based on the observations of the particle radiation monitor (PRM) of the fourth of the China-Brazil Earth Resource Satellites (CBERS-4). The flux remained low for approximately 11 d; it did not recover after a small magnetic storm on January 26 but after a small magnetic storm on February 2. The loss and recovery of the relativistic electrons during this event are investigated using the PRM data, medium- and high-energy electron observations of NOAA-15 and the Van Allen Probes, medium-energy electron observations of GOES-13, and wave observations of the Van Allen Probes. This study shows that the loss of energetic electrons in this event is related to magnetospheric compression. The chorus waves accelerate the medium-energy electrons, which causes the recovery of relativistic electrons. The Van Allen Probes detected strong chorus waves in the region L = 3\textendash6 from January 21 to February 2. However, the flux of medium-energy electrons was low in the region. This implies that the long-lasting lack of recovery of the relativistic electrons after this event is due to the lack of the medium-energy \textquotedblleftseed\textquotedblright electrons. The medium-energy electrons in the outer radiation belt may be a clue to predict the recovery of relativistic electrons. Chen, Zhe; Chen, HongFei; Li, YiFan; Xiang, HongWen; Yu, XiangQian; Shi, WeiHong; Hao, ZhiHua; Zou, Hong; Zou, JiQing; Zhong, WeiYing; Published by: Science China Technological Sciences Published on: 04/2017 YEAR: 2017 DOI: 10.1007/s11431-016-9008-3 outer radiation belt high-energy electrons medium-energy electrons space environment; Van Allen Probes |
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Bayesian Spectral Analysis of Chorus Sub-Elements from the Van Allen Probes We develop a Bayesian spectral analysis technique that calculates the probability distribution functions of a superposition of wave-modes each described by a linear growth rate, a frequency and a chirp rate. The Bayesian framework has a number of advantages, including 1) reducing the parameter space by integrating over the amplitude and phase of the wave, 2) incorporating the data from each channel to determine the model parameters such as frequency which leads to high resolution results in frequency and time, 3) the ability to consider the superposition of waves where the wave-parameters are closely spaced, 4) the ability to directly calculate the expectation value of wave parameters without resorting to ensemble averages, 5) the ability to calculate error bars on model parameters. We examine one rising-tone chorus element in detail from a disturbed time on November 14, 2012 using burst mode waveform data of the three components of the electric and magnetic field from the EMFISIS instrument on board NASA\textquoterights Van Allen Probes. The results demonstrate that sub-elements are likely composed of almost linear waves that are nearly parallel propagating with continuously changing wave parameters such as frequency and wave-vector. Between sub-elements the wave parameters of the dominant mode undergoes a discrete change in frequency and wave-vector. Near the boundary of sub-elements multiple waves are observed such that the evolution of the waves is reminiscent of wave-wave processes such as parametric decay or nonlinear induced scattering by particles. These nonlinear processes may affect the saturation of the whistler-mode chorus instability. Crabtree, Chris; Tejero, Erik; Ganguli, Gurudas; Hospodarsky, George; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023547 |
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Generation of extremely low frequency chorus in Van Allen radiation belts Recent studies have shown that chorus can efficiently accelerate the outer radiation belt electrons to relativistic energies. Chorus, previously often observed above 0.1 equatorial electron gyrofrequency fce, was generated by energetic electrons originating from Earth\textquoterights plasma sheet. Chorus below 0.1 fce has seldom been reported until the recent data from Van Allen Probes, but its origin has not been revealed so far. Because electron resonant energy can approach the relativistic level at extremely low frequency, relativistic effects should be considered in the formula for whistler mode wave growth rate. Here we report high-resolution observations during the 14 October 2014 small storm and firstly demonstrate, using a fully relativistic simulation, that electrons with the high-energy tail population and relativistic pitch angle anisotropy can provide free energy sufficient for generating chorus below 0.1 fce. The simulated wave growth displays a very similar pattern to the observations. The current results can be applied to Jupiter, Saturn, and other magnetized planets. Xiao, Fuliang; Liu, Si; Tao, Xin; Su, Zhenpeng; Zhou, Qinghua; Yang, Chang; He, Zhaoguo; He, Yihua; Gao, Zhonglei; Baker, D.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023561 ELF chorus waves; RBSP results; relativistic distribution; Van Allen Probes; Wave-particle interaction |
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A technique to quantitatively determine the sheath impedance of the Van Allen Probes Electric Field and Waves (EFW) instrument is presented. This is achieved, for whistler mode waves, through a comparison between the total electric field wave power spectra calculated from magnetic field observations and cold plasma theory, and the total electric field wave power measured by the EFW spherical double probes instrument. In a previous study, a simple density-dependent sheath impedance model was developed in order to account for the differences between the observed and calculated wave electric field. The current study builds on this previous work by investigating the remaining discrepancies, identifying their cause, and developing an improved sheath impedance correction. Analysis reveals that anomalous gains are caused by the spin axis antennas measuring too much electric field at specific densities and frequencies. This is accounted for in an improved sheath impedance model by introducing a density-dependent function describing the relative effective length of the probe separation, Leff, in addition to the sheath capacitance and resistance values previously calculated. Leff values vary between between 0.5 and 1.2, with values >1 accounting for the anomalous gains and values <1 accounting for the shorting effect at low densities. Applying this improved sheath impedance model results in a significant increase in the agreement level between observed and calculated electric field power spectra and wave powers over the previous model. Hartley, D.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Bounds, S.; Averkamp, T.; Bonnell, J.; ik, O.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023597 antenna sheath impedance; EFW; electric field; EMFISIS; Van Allen Probes; whistler mode waves |
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Zhang, Yang; Shi, Run; Ni, Binbin; Gu, Xudong; Zhang, Xianguo; Zuo, Pingbing; Fu, Song; Xiang, Zheng; Wang, Qi; Cao, Xing; Zou, Zhengyang; Published by: Advances in Space Research Published on: 03/2017 YEAR: 2017 DOI: 10.1016/j.asr.2016.12.035 |
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Zhang, Yang; Shi, Run; Ni, Binbin; Gu, Xudong; Zhang, Xianguo; Zuo, Pingbing; Fu, Song; Xiang, Zheng; Wang, Qi; Cao, Xing; Zou, Zhengyang; Published by: Advances in Space Research Published on: 03/2017 YEAR: 2017 DOI: 10.1016/j.asr.2016.12.035 |
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Zhang, Yang; Shi, Run; Ni, Binbin; Gu, Xudong; Zhang, Xianguo; Zuo, Pingbing; Fu, Song; Xiang, Zheng; Wang, Qi; Cao, Xing; Zou, Zhengyang; Published by: Advances in Space Research Published on: 03/2017 YEAR: 2017 DOI: 10.1016/j.asr.2016.12.035 |
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Zhang, Yang; Shi, Run; Ni, Binbin; Gu, Xudong; Zhang, Xianguo; Zuo, Pingbing; Fu, Song; Xiang, Zheng; Wang, Qi; Cao, Xing; Zou, Zhengyang; Published by: Advances in Space Research Published on: 03/2017 YEAR: 2017 DOI: 10.1016/j.asr.2016.12.035 |
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We have studied the spatial location relative to the plasmapause (PP) of the most intense electromagnetic ion cyclotron (EMIC) waves observed on Van Allen Probes A and B during their first full precession in local time. Most of these waves occurred over an L range of from -1 to +2 RE relative to the PP. Very few events occurred only within 0.1 RE of the PP, and events with a width in L of < 0.2 REoccurred both inside and outside the PP. Wave occurrence was always associated with high densities of ring current ions; plasma density gradients or enhancements were associated with some events but were not dominant factors in determining the sites of wave generation. Storm main and recovery phase events in the dusk sector were often inside the PP, and dayside events during quiet times and compressions of the magnetosphere were more evenly distributed both inside and outside the PP. Superposed epoch analyses of the dependence of wave onset on solar wind dynamic pressure (Psw), the SME (SuperMAG auroral electrojet) index, and the SYM/H index showed that substorm injections and solar wind compressions were temporally closely associated with EMIC wave onset, but to an extent that varied with frequency band, MLT, and storm phase, and location relative to the PP. The fact that increases in SME and Psw were less strongly correlated with events at the PP than with other events might suggest that the occurrence of those events was affected by the density gradient. Tetrick, S.; Engebretson, M.; Posch, J.; Olson, C.; Smith, C.; Denton, R.; Thaller, S.; Wygant, J.; Reeves, G.; MacDonald, E.; Fennell, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023392 |
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Oxygen cyclotron harmonic waves observed by the Van Allen Probes Fine structured multiple-harmonic electromagnetic emissions at frequencies around the equatorial oxygen cyclotron harmonics are observed by Van Allen Probe A outside the core plasmasphere (L~5) off the magnetic equator (MLAT~-7.5\textdegree) during a magnetic storm. We find that the multiple-harmonic emissions have their PSD peaks at 2~8 equatorial oxygen gyro-harmonics (f~nfO+, n=2~8) while the fundamental mode (n=1) is absent, implying that the harmonic waves are generated near the equator and propagate into the observation region. Additionally these electromagnetic emissions are linear polarized. Different from the equatorial noise emission propagating very obliquely, these emissions have moderate wave normal angles (about 40\textdegree~60\textdegree) which predominately become larger as the harmonic number increases. Considering their frequency and wave normal angle characteristics, it is suggested that these multiple-harmonic emissions might play an important role in the dynamic variation of radiation belt electrons. Xiongdong, Yu; Zhigang, Yuan; Dedong, Wang; Shiyong, Huang; Haimeng, Li; Tao, Yu; Zheng, Qiao; Published by: Science China: Earth Sciences Published on: 03/2017 YEAR: 2017 DOI: 10.1007/s11430-016-9024-3 Oxygen Cyclotron Harmonic Waves; Radiation belt; Ring current ions; Van Allen Probes |
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Energetic (hundreds of keV) electrons in the radiation belt slot region have been found to exhibit the butterfly pitch angle distributions. Resonant interactions with magnetosonic and whistler-mode waves are two potential mechanisms for the formation of these peculiar distributions. Here we perform a statistical study of energetic electron pitch angle distribution characteristics measured by Van Allen Probes in the slot region during a three-year period from May 2013 to May 2016. Our results show that electron butterfly distributions are closely related to magnetosonic waves rather than to whistler-mode waves. Both electron butterfly distributions and magnetosonic waves occur more frequently at the geomagnetically active times than at the quiet times. In a statistical sense, more distinct butterfly distributions usually correspond to magnetosonic waves with larger amplitudes and vice versa. The averaged magnetosonic wave amplitude is less than 5 pT in the case of normal and flat-top distributions with a butterfly index BI = 1 but reaches \~ 35\textendash95 pT in the case of distinct butterfly distributions with BI > 1.3. For magnetosonic waves with amplitudes >50 pT, the occurrence rate of butterfly distribution is above 80\%. Our study suggests that energetic electron butterfly distributions in the slot region are primarily caused by magnetosonic waves. Yang, Chang; Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Wang, Shui; Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Funsten, H.; Published by: Geophysical Research Letters Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2017GL073116 butterfly distributions; Electron acceleration; Landau resonance; magnetosonic wave; Radiation belt; Van Allen Probes; Wave-particle interaction |
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Energetic (hundreds of keV) electrons in the radiation belt slot region have been found to exhibit the butterfly pitch angle distributions. Resonant interactions with magnetosonic and whistler-mode waves are two potential mechanisms for the formation of these peculiar distributions. Here we perform a statistical study of energetic electron pitch angle distribution characteristics measured by Van Allen Probes in the slot region during a three-year period from May 2013 to May 2016. Our results show that electron butterfly distributions are closely related to magnetosonic waves rather than to whistler-mode waves. Both electron butterfly distributions and magnetosonic waves occur more frequently at the geomagnetically active times than at the quiet times. In a statistical sense, more distinct butterfly distributions usually correspond to magnetosonic waves with larger amplitudes and vice versa. The averaged magnetosonic wave amplitude is less than 5 pT in the case of normal and flat-top distributions with a butterfly index BI = 1 but reaches \~ 35\textendash95 pT in the case of distinct butterfly distributions with BI > 1.3. For magnetosonic waves with amplitudes >50 pT, the occurrence rate of butterfly distribution is above 80\%. Our study suggests that energetic electron butterfly distributions in the slot region are primarily caused by magnetosonic waves. Yang, Chang; Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Wang, Shui; Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Funsten, H.; Published by: Geophysical Research Letters Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2017GL073116 butterfly distributions; Electron acceleration; Landau resonance; magnetosonic wave; Radiation belt; Van Allen Probes; Wave-particle interaction |
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Energetic (hundreds of keV) electrons in the radiation belt slot region have been found to exhibit the butterfly pitch angle distributions. Resonant interactions with magnetosonic and whistler-mode waves are two potential mechanisms for the formation of these peculiar distributions. Here we perform a statistical study of energetic electron pitch angle distribution characteristics measured by Van Allen Probes in the slot region during a three-year period from May 2013 to May 2016. Our results show that electron butterfly distributions are closely related to magnetosonic waves rather than to whistler-mode waves. Both electron butterfly distributions and magnetosonic waves occur more frequently at the geomagnetically active times than at the quiet times. In a statistical sense, more distinct butterfly distributions usually correspond to magnetosonic waves with larger amplitudes and vice versa. The averaged magnetosonic wave amplitude is less than 5 pT in the case of normal and flat-top distributions with a butterfly index BI = 1 but reaches \~ 35\textendash95 pT in the case of distinct butterfly distributions with BI > 1.3. For magnetosonic waves with amplitudes >50 pT, the occurrence rate of butterfly distribution is above 80\%. Our study suggests that energetic electron butterfly distributions in the slot region are primarily caused by magnetosonic waves. Yang, Chang; Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Wang, Shui; Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Funsten, H.; Published by: Geophysical Research Letters Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2017GL073116 butterfly distributions; Electron acceleration; Landau resonance; magnetosonic wave; Radiation belt; Van Allen Probes; Wave-particle interaction |
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Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector 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 field fluctuations have a finite compressional component due to small but finite plasma beta (\~0.1); (3) the energetic proton fluxes in the energy ranging from above 10 keV to about 100 keV exhibit pulsations with the same frequency as the poloidal mode and energy-dependent phase delays relative to the azimuthal component of the electric field, providing evidence for drift-bounce resonance; and (4) the second harmonic poloidal mode may have been excited via the drift-bounce resonance mechanism with free energy fed by the inward radial gradient of \~80 keV protons. We show that the wave active region is where the plume overlaps the outer edge of ring current and suggest that this region can have a wide longitudinal extent near geosynchronous orbit. Min, Kyungguk; Takahashi, Kazue; Ukhorskiy, Aleksandr; Manweiler, Jerry; Spence, Harlan; Singer, Howard; Claudepierre, Seth; Larsen, Brian; Soto-Chavez, Rualdo; Cohen, Ross; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023770 drift-bounce resonance; high m ULF waves; Second harmonic poloidal mode; Van Allen Probes |
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In September 2014 an unusually long-lasting (≳10 days) ultra-relativistic electron flux depletion occurred in the outer radiation belt despite ongoing solar wind forcing. We simulate this period using a ULF wave radial diffusion model, driven by observed ULF wave power coupled to flux variations at the outer boundary at L* = 5, including empirical electron loss models due to chorus and hiss wave scattering. Our results show that unexplained rapid main phase loss, that depletes the belt within hours, is essential to explain the observations. Such ultra-relativistic electron extinction decouples the prestorm and poststorm fluxes, revealing the subsequent belt dynamics to be surprisingly independent of prestorm flux. However, once this extinction is included, ULF wave transport and coupling to the outer boundary explain the extended depletion event and also the eventual flux recovery. Neither local acceleration nor ongoing losses from hiss or chorus wave scattering to the atmosphere are required. Ozeke, Louis; Mann, Ian; Murphy, Kyle; Sibeck, David; Baker, Daniel; Published by: Geophysical Research Letters Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2017GL072811 radial diffusion; Radiation belt; ULF waves; ultrarelativistic; Van Allen Probes; wave-particle interactions |
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We present observations from the Van Allen Probes spacecraft that identify a region of intense whistler mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became nonlinearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement. Woodroffe, J.; Jordanova, V.; Funsten, H.; Streltsov, A.; Bengtson, M.; Kletzing, C.; Wygant, J.; Thaller, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2015JA022219 Ducting; Van Allen Probes; wave-particle interactions; Whistlers |
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We present observations from the Van Allen Probes spacecraft that identify a region of intense whistler mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became nonlinearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement. Woodroffe, J.; Jordanova, V.; Funsten, H.; Streltsov, A.; Bengtson, M.; Kletzing, C.; Wygant, J.; Thaller, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2015JA022219 Ducting; Van Allen Probes; wave-particle interactions; Whistlers |
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We present observations from the Van Allen Probes spacecraft that identify a region of intense whistler mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became nonlinearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement. Woodroffe, J.; Jordanova, V.; Funsten, H.; Streltsov, A.; Bengtson, M.; Kletzing, C.; Wygant, J.; Thaller, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2015JA022219 Ducting; Van Allen Probes; wave-particle interactions; Whistlers |
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Whistler mode chorus is one of the most important emissions affecting the energization of the radiation belts. Recent laboratory experiments that inject energetic electron beams into a cold plasma have revealed several spectral features in the nonlinear evolution of these instabilities that have also been observed in high-time resolution in situ wave-form data. These features include (1) a sub-element structure which consists of an amplitude modulation on time-scales slower than the bounce time, (2) closely spaced discrete frequency hopping that results in a faster apparent frequency chirp rate, (3) fast frequency changes near the sub-element boundaries, and (4) harmonic generation. In this paper, we develop a finite dimensional self-consistent Hamiltonian model for the evolution of the resonant beam of electrons. We analyze a single wave case and demonstrate that the instability occurs due to a Krein collision, which manifests as a coupling between a negative and positive energy mode. This analysis revealed that the nonlinear evolution of the spectrally stable fixed-points of the self-consistent Hamiltonian develop a sub-packet structure similar to that of space observations. We then analyze the case of two whistler waves to show that the model reproduces the nonlinear harmonic generation and leads to a hypothesis for the closely spaced frequency hopping observed in laboratory experiments and space data. Crabtree, Chris; Ganguli, Gurudas; Tejero, Erik; Published by: Physics of Plasmas Published on: 03/2017 YEAR: 2017 DOI: 10.1063/1.4977539 Dispersion relations; Electron beams; SingingEigenvalues; Van Allen Probes; Whistler waves |
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Chorus whistler wave source scales as determined from multipoint Van Allen Probe measurements Whistler mode chorus waves are particularly important in outer radiation belt dynamics due to their key role in controlling the acceleration and scattering of electrons over a very wide energy range. The key parameters for both nonlinear and quasi-linear treatment of wave-particle interactions are the temporal and spatial scales of the wave source region and coherence of the wave field perturbations. Neither the source scale nor the coherence scale is well established experimentally, mostly because of a lack of multipoint VLF waveform measurements. We present an unprecedentedly long interval of coordinated VLF waveform measurements (sampled at 16384 s-1) aboard the two Van Allen Probes spacecraft\textemdash9 h (0800\textendash1200 UT and 1700\textendash2200 UT) during two consecutive apogees on 15 July 2014. The spacecraft separations varied from about 100 to 5000 km (mostly radially); measurements covered an L shell range from 3 to 6; magnetic local time 0430\textendash0900, and magnetic latitudes were ~15 and ~5\textdegree during the two orbits. Using time-domain correlation techniques, the single chorus source spatial extent transverse to the background magnetic field has been determined to be about 550\textendash650 km for upper band chorus waves with amplitudes less than 100 pT and up to 800 km for larger amplitude, lower band chorus waves. The ratio between wave amplitudes measured on the two spacecraft is also examined to reveal that the wave amplitude distribution within a single chorus element generation area can be well approximated by a Gaussian exp(-0.5 \textperiodcentered r2/r02), with the characteristic scale r0 around 300 km. Waves detected by the two spacecraft were found to be coherent in phase at distances up to 400 km. Agapitov, O.; Blum, L.; Mozer, F.; Bonnell, J.; Wygant, J.; Published by: Geophysical Research Letters Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2017GL072701 |
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Accurate knowledge of the plasma fluxes in the inner magnetosphere is essential for both scientific and programmatic applications. Knowledge of the low-energy electrons (approximately tens to hundreds of eV) in the inner magnetosphere is particularly important since these electrons are acted upon by various physical processes, accelerating the electrons to higher energies, and also causing their loss. However, measurements of low-energy electrons are challenging, and as a result, this population has been somewhat neglected previously. This study concerns observations of low-energy electrons made by the Helium Oxygen Proton Electron instrument on board the Van Allen Probes satellites and also observations from geosynchronous orbit made by the Magnetospheric Plasma Analyzer on board Los Alamos National Laboratory satellites. The fluxes of electrons from ~30 eV to 1 keV are quantified as a function of pitch-angle, McIlwain L parameter, and local time for both quiet and active periods. Results indicate two sources for low-energy electrons in this energy range: the low-energy tail of the electron plasma sheet and the high-energy tail of the dayside ionosphere. These populations are identified primarily as a result of their different pitch-angle distributions. Field-aligned outflows from the dayside ionosphere are observed at all L shells during quiet and active periods. Our results also demonstrate that the dayside electron field-aligned fluxes at ~30 eV are particularly strong between L values of 6 and 7, indicating an enhanced source within the polar ionosphere. Denton, M.; Reeves, G.; Larsen, B.; Friedel, R.; Thomsen, M.; Fernandes, P.; Skoug, R.; Funsten, H.; Sarno-Smith, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023648 |
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The Van Allen Probes have reported frequent flux enhancements of 100s keV electrons in the slot region, with lower energy electrons exhibiting more dynamic behavior at lower L shells. Also, in situ electric field measurements from the Combined Release and Radiation Effects Satellite, Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Van Allen Probes have provided evidence for large-scale electric fields at low L shells during active times. We study an event on 19 February 2014 where hundreds of keV electron fluxes were enhanced by orders of magnitude in the slot region and electric fields of 1\textendash2 mV/m were observed below L = 3. Using a 2-D guiding center particle tracer and a simple large-scale convection electric field model, we demonstrate that the measured electric fields can account for energization of electrons up to at least 500 keV in the slot region through inward radial transport. Califf, S.; Li, X.; Zhao, H.; Kellerman, A.; Sarris, T.; Jaynes, A.; Malaspina, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023657 convection; electric field; electrons; Slot region; Van Allen Probes |
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Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector This paper presents observations of ultra-low frequency (ULF) waves from Van Allen Probes. The event that generated the ULF waves occurred two 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 pre-midnight 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 field fluctuations have a finite compressional component due to small but finite plasma beta (\~0.1); (3) the energetic proton fluxes in the energy ranging from above 10 keV to about 100 keV exhibit pulsations with the same frequency as the poloidal mode and energy-dependent phase delays relative to the azimuthal component of the electric field, providing evidence for drift-bounce resonance; and (4) the second harmonic poloidal mode may have been excited via the drift-bounce resonance mechanism with free energy fed by the inward radial gradient of \~80 keV protons. We show that the wave active region is where the plume overlaps the outer edge of ring current and suggest that this region can have a wide longitudinal extent near geosynchronous orbit. Min, Kyungguk; Takahashi, Kazue; Ukhorskiy, Aleksandr; Manweiler, Jerry; Spence, Harlan; Singer, Howard; Claudepierre, Seth; Larsen, Brian; Soto-Chavez, Rualdo; Cohen, Ross; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023770 drift-bounce resonance; high m ULF waves; Second harmonic poloidal mode; Van Allen Probes |
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We present Van Allen Probe observation of drift-resonance interaction between energetic electrons and ultralow frequency (ULF) waves on 29 October 2013. Oscillations in electron flux were observed at the period of \~450 s, which is also the dominant period of the observed ULF magnetic pulsations. The phase shift of the electron fluxes (\~50 to 150 keV) across the estimated resonant energy (\~104 keV) is \~360\textdegree. This phase relationship is different from the characteristic 180\textdegree phase shift as expected from the drift-resonance theory. We speculate that the additional 180\textdegree phase difference arises from the inversion of electron phase space density (PSD) gradient, which in turn is caused by the drift motion of the substorm injected electrons. This PSD gradient adjusts the characteristic particle signatures in the drift-resonance theory, which indicates a coupling effect between the magnetotail and the radiation belt and helps to better understand the wave-particle interaction in the magnetosphere. Chen, X.-R.; Zong, Q.-G.; Zhou, X.-Z.; Blake, Bernard; Wygant, J.; Kletzing, C.; Published by: Geophysical Research Letters Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016GL071252 drift resonance; injection; PSD gradient; ULF waves; Van Allen Probes |
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We present observations from the Van Allen Probes spacecraft that identify an region of intense whistler-mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became non-linearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement. Woodroffe, J.; Jordanova, V.; Funsten, H.; Streltsov, A.; Bengtson, M.; Kletzing, C.; Wygant, J.; Thaller, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2015JA022219 Ducting; Van Allen Probes; wave-particle interactions; Whistlers |
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We present observations from the Van Allen Probes spacecraft that identify an region of intense whistler-mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became non-linearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement. Woodroffe, J.; Jordanova, V.; Funsten, H.; Streltsov, A.; Bengtson, M.; Kletzing, C.; Wygant, J.; Thaller, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2015JA022219 Ducting; Van Allen Probes; wave-particle interactions; Whistlers |
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We present observations from the Van Allen Probes spacecraft that identify an region of intense whistler-mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became non-linearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement. Woodroffe, J.; Jordanova, V.; Funsten, H.; Streltsov, A.; Bengtson, M.; Kletzing, C.; Wygant, J.; Thaller, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2015JA022219 Ducting; Van Allen Probes; wave-particle interactions; Whistlers |
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Utilizing simultaneous twin Van Allen Probes observations of whistler mode waves at variable separations, we are able to distinguish the temporal variations from spatial variations, determine the coherence spatial scale, and suggest the possible mechanism of wave modulation. The two probes observed coherently modulated whistler mode waves simultaneously at an unexpectedly large distance up to ~4.3 RE over 3 h during a relatively quiet period. The modulation of 150\textendash500 Hz plasmaspheric hiss was correlated with whistler mode waves measured outside the plasmasphere across 3 h in magnetic local time and 3 L shells, revealing that the modulation was temporal in nature. We suggest that the coherent modulation of whistler mode waves was associated with the coherent ULF waves measured over a large scale, which modulate the plasmaspheric density and result in the modulation of hiss waves via local amplification. In a later period, the 500\textendash1500 Hz periodic rising-tone whistler mode waves were strongly correlated when the two probes traversed large spatial regions and even across the plasmapause. These periodic rising-tone emissions recurred with roughly the same period as the ULF wave, but there was no one-to-one correspondence, and a cross-correlation analysis suggests that they possibly originated from large L shells although the actual cause needs further investigation. Li, Jinxing; Bortnik, Jacob; Li, Wen; Thorne, Richard; Ma, Qianli; Chu, Xiangning; Chen, Lunjin; Kletzing, Craig; Kurth, William; Hospodarsky, George; Wygant, John; Breneman, Aaron; Thaller, Scott; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023706 coherent waves; multisatellite; periodic rising tone; Van Allen Probes; whistler mode |
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Utilizing simultaneous twin Van Allen Probes observations of whistler mode waves at variable separations, we are able to distinguish the temporal variations from spatial variations, determine the coherence spatial scale, and suggest the possible mechanism of wave modulation. The two probes observed coherently modulated whistler mode waves simultaneously at an unexpectedly large distance up to ~4.3 RE over 3 h during a relatively quiet period. The modulation of 150\textendash500 Hz plasmaspheric hiss was correlated with whistler mode waves measured outside the plasmasphere across 3 h in magnetic local time and 3 L shells, revealing that the modulation was temporal in nature. We suggest that the coherent modulation of whistler mode waves was associated with the coherent ULF waves measured over a large scale, which modulate the plasmaspheric density and result in the modulation of hiss waves via local amplification. In a later period, the 500\textendash1500 Hz periodic rising-tone whistler mode waves were strongly correlated when the two probes traversed large spatial regions and even across the plasmapause. These periodic rising-tone emissions recurred with roughly the same period as the ULF wave, but there was no one-to-one correspondence, and a cross-correlation analysis suggests that they possibly originated from large L shells although the actual cause needs further investigation. Li, Jinxing; Bortnik, Jacob; Li, Wen; Thorne, Richard; Ma, Qianli; Chu, Xiangning; Chen, Lunjin; Kletzing, Craig; Kurth, William; Hospodarsky, George; Wygant, John; Breneman, Aaron; Thaller, Scott; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023706 coherent waves; multisatellite; periodic rising tone; Van Allen Probes; whistler mode |
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Utilizing simultaneous twin Van Allen Probes observations of whistler mode waves at variable separations, we are able to distinguish the temporal variations from spatial variations, determine the coherence spatial scale, and suggest the possible mechanism of wave modulation. The two probes observed coherently modulated whistler mode waves simultaneously at an unexpectedly large distance up to ~4.3 RE over 3 h during a relatively quiet period. The modulation of 150\textendash500 Hz plasmaspheric hiss was correlated with whistler mode waves measured outside the plasmasphere across 3 h in magnetic local time and 3 L shells, revealing that the modulation was temporal in nature. We suggest that the coherent modulation of whistler mode waves was associated with the coherent ULF waves measured over a large scale, which modulate the plasmaspheric density and result in the modulation of hiss waves via local amplification. In a later period, the 500\textendash1500 Hz periodic rising-tone whistler mode waves were strongly correlated when the two probes traversed large spatial regions and even across the plasmapause. These periodic rising-tone emissions recurred with roughly the same period as the ULF wave, but there was no one-to-one correspondence, and a cross-correlation analysis suggests that they possibly originated from large L shells although the actual cause needs further investigation. Li, Jinxing; Bortnik, Jacob; Li, Wen; Thorne, Richard; Ma, Qianli; Chu, Xiangning; Chen, Lunjin; Kletzing, Craig; Kurth, William; Hospodarsky, George; Wygant, John; Breneman, Aaron; Thaller, Scott; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023706 coherent waves; multisatellite; periodic rising tone; Van Allen Probes; whistler mode |
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Utilizing simultaneous twin Van Allen Probes observations of whistler mode waves at variable separations, we are able to distinguish the temporal variations from spatial variations, determine the coherence spatial scale, and suggest the possible mechanism of wave modulation. The two probes observed coherently modulated whistler mode waves simultaneously at an unexpectedly large distance up to ~4.3 RE over 3 h during a relatively quiet period. The modulation of 150\textendash500 Hz plasmaspheric hiss was correlated with whistler mode waves measured outside the plasmasphere across 3 h in magnetic local time and 3 L shells, revealing that the modulation was temporal in nature. We suggest that the coherent modulation of whistler mode waves was associated with the coherent ULF waves measured over a large scale, which modulate the plasmaspheric density and result in the modulation of hiss waves via local amplification. In a later period, the 500\textendash1500 Hz periodic rising-tone whistler mode waves were strongly correlated when the two probes traversed large spatial regions and even across the plasmapause. These periodic rising-tone emissions recurred with roughly the same period as the ULF wave, but there was no one-to-one correspondence, and a cross-correlation analysis suggests that they possibly originated from large L shells although the actual cause needs further investigation. Li, Jinxing; Bortnik, Jacob; Li, Wen; Thorne, Richard; Ma, Qianli; Chu, Xiangning; Chen, Lunjin; Kletzing, Craig; Kurth, William; Hospodarsky, George; Wygant, John; Breneman, Aaron; Thaller, Scott; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2017 YEAR: 2017 DOI: 10.1002/2016JA023706 coherent waves; multisatellite; periodic rising tone; Van Allen Probes; whistler mode |
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Externally driven plasmaspheric ULF waves observed by the Van Allen Probes 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 ultralow frequency (ULF) waves. The waves exhibited strong spectral power in the 5\textendash40 mHz band and included multiharmonic toroidal waves visible up to the eleventh 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 by the cross-phase analysis of data from the two spacecraft. We also find that the coherence and phase delay of the azimuthal components of the magnetic field from the two spacecraft strongly depend on the radial separation of the spacecraft and attribute this feature to field line resonance effects. Finally, using the observed toroidal wave frequencies, we estimate the plasma mass density for L = 2.6\textendash5.8. By comparing the mass density with the electron number density that is estimated from the spectrum of plasma waves, we infer that the plasma was dominated by H+ ions and was distributed uniformly along the magnetic field lines. The electron density is higher than the prediction of saturated plasmasphere models, and this \textquotedblleftsuper saturated\textquotedblright plasmasphere and the uniform ion distribution are consistent with the low geomagnetic activity that prevailed. Takahashi, Kazue; Denton, Richard; Kurth, William; Kletzing, Craig; Wygant, John; Bonnell, John; Dai, Lei; Min, Kyungguk; Smith, Charles; MacDowall, Robert; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2014JA020373 multispacecraft observation; plasmasphere; ULF waves; Van Allen Probes |
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Using observations from NASA\textquoterights Van Allen Probes, we study the role of sudden particle enhancements at low L shells (SPELLS) as a source of inner radiation belt electrons. SPELLS events are characterized by electron intensity enhancements of approximately an order of magnitude or more in less than 1 day at L < 3. During quiet and average geomagnetic conditions, the phase space density radial distributions for fixed first and second adiabatic invariants are peaked at 2 < L < 3 for electrons ranging in energy from ~50 keV to ~1 MeV, indicating that slow inward radial diffusion is not the dominant source of inner belt electrons under quiet/average conditions. During SPELLS events, the evolution of electron distributions reveals an enhancement of phase space density that can exceed 3 orders of magnitude in the slot region and continues into the inner radiation belt, which is evidence that these events are an important\textemdashand potentially dominant\textemdashsource of inner belt electrons. Electron fluxes from September 2012 through February 2016 reveal that SPELLS occur frequently (~2.5/month at 200 keV), but the number of observed events decreases exponentially with increasing electron energy for >=100 keV. After SPELLS events, the slot region reforms due to slow energy-dependent decay over several day time scales, consistent with losses due to interactions with plasmaspheric hiss. Combined, these results indicate that the peaked phase space density distributions in the inner electron radiation belt result from an \textquotedbllefton/off,\textquotedblright geomagnetic-activity-dependent source from higher radial distances. Turner, D.; O\textquoterightBrien, T.; Fennell, J.; Claudepierre, S.; Blake, J.; Jaynes, A.; Baker, D.; Kaneka, S.; Gkioulidou, M.; Henderson, M.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1029/1999JA900445 energetic particle injections; inner magnetosphere; Radiation belts; relativistic electrons; Van Allen Probes |
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We analyze a wave event that occurred near noon between 07:03 and 07:08 UT on 23 February 2014 detected by the Van Allen Probes B spacecraft, where waves in the lower hybrid frequency range (LHFR) and electromagnetic ion cyclotron (EMIC) waves are observed to be highly correlated, with Pearson correlation coefficient of ~0.86. We assume that the correlation is the result of LHFR wave generation by the ions\textquoteright polarization drift in the electric field of the EMIC waves. To check this assumption the drift velocities of electrons and H+, He+, and O+ ions in the measured EMIC wave electric field were modeled. Then the LHFR wave linear instantaneous growth rates for plasma with these changing drift velocities and different plasma compositions were calculated. The time distribution of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD) parallel and perpendicular to the ambient magnetic field to the total PSD were found. These characteristics of the growth rates were compared with the corresponding characteristics of the observed LHFR activity. Reasonable agreement between these features and the strong correlation between EMIC and LHFR energy densities support the assumption that the LHFR wave generation can be caused by the ions\textquoteright polarization drift in the electric field of an EMIC wave. Khazanov, G.; Boardsen, S.; Krivorutsky, E.; Engebretson, M.; Sibeck, D.; Chen, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA022814 nonlinear phenomena; parametric processes; Van Allen Probes; wave/wave interactions |
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We analyze a wave event that occurred near noon between 07:03 and 07:08 UT on 23 February 2014 detected by the Van Allen Probes B spacecraft, where waves in the lower hybrid frequency range (LHFR) and electromagnetic ion cyclotron (EMIC) waves are observed to be highly correlated, with Pearson correlation coefficient of ~0.86. We assume that the correlation is the result of LHFR wave generation by the ions\textquoteright polarization drift in the electric field of the EMIC waves. To check this assumption the drift velocities of electrons and H+, He+, and O+ ions in the measured EMIC wave electric field were modeled. Then the LHFR wave linear instantaneous growth rates for plasma with these changing drift velocities and different plasma compositions were calculated. The time distribution of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD) parallel and perpendicular to the ambient magnetic field to the total PSD were found. These characteristics of the growth rates were compared with the corresponding characteristics of the observed LHFR activity. Reasonable agreement between these features and the strong correlation between EMIC and LHFR energy densities support the assumption that the LHFR wave generation can be caused by the ions\textquoteright polarization drift in the electric field of an EMIC wave. Khazanov, G.; Boardsen, S.; Krivorutsky, E.; Engebretson, M.; Sibeck, D.; Chen, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA022814 nonlinear phenomena; parametric processes; Van Allen Probes; wave/wave interactions |
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We analyze a wave event that occurred near noon between 07:03 and 07:08 UT on 23 February 2014 detected by the Van Allen Probes B spacecraft, where waves in the lower hybrid frequency range (LHFR) and electromagnetic ion cyclotron (EMIC) waves are observed to be highly correlated, with Pearson correlation coefficient of ~0.86. We assume that the correlation is the result of LHFR wave generation by the ions\textquoteright polarization drift in the electric field of the EMIC waves. To check this assumption the drift velocities of electrons and H+, He+, and O+ ions in the measured EMIC wave electric field were modeled. Then the LHFR wave linear instantaneous growth rates for plasma with these changing drift velocities and different plasma compositions were calculated. The time distribution of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD) parallel and perpendicular to the ambient magnetic field to the total PSD were found. These characteristics of the growth rates were compared with the corresponding characteristics of the observed LHFR activity. Reasonable agreement between these features and the strong correlation between EMIC and LHFR energy densities support the assumption that the LHFR wave generation can be caused by the ions\textquoteright polarization drift in the electric field of an EMIC wave. Khazanov, G.; Boardsen, S.; Krivorutsky, E.; Engebretson, M.; Sibeck, D.; Chen, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA022814 nonlinear phenomena; parametric processes; Van Allen Probes; wave/wave interactions |
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We analyze a wave event that occurred near noon between 07:03 and 07:08 UT on 23 February 2014 detected by the Van Allen Probes B spacecraft, where waves in the lower hybrid frequency range (LHFR) and electromagnetic ion cyclotron (EMIC) waves are observed to be highly correlated, with Pearson correlation coefficient of ~0.86. We assume that the correlation is the result of LHFR wave generation by the ions\textquoteright polarization drift in the electric field of the EMIC waves. To check this assumption the drift velocities of electrons and H+, He+, and O+ ions in the measured EMIC wave electric field were modeled. Then the LHFR wave linear instantaneous growth rates for plasma with these changing drift velocities and different plasma compositions were calculated. The time distribution of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD) parallel and perpendicular to the ambient magnetic field to the total PSD were found. These characteristics of the growth rates were compared with the corresponding characteristics of the observed LHFR activity. Reasonable agreement between these features and the strong correlation between EMIC and LHFR energy densities support the assumption that the LHFR wave generation can be caused by the ions\textquoteright polarization drift in the electric field of an EMIC wave. Khazanov, G.; Boardsen, S.; Krivorutsky, E.; Engebretson, M.; Sibeck, D.; Chen, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA022814 nonlinear phenomena; parametric processes; Van Allen Probes; wave/wave interactions |
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Accurate knowledge of the plasma fluxes in the inner magnetosphere is essential for both scientific and programmatic applications. Knowledge of the low-energy electrons (approximately tens to hundreds of eV) in the inner magnetosphere is particularly important since these electrons are acted upon by various physical processes, accelerating the electrons to higher energies, and also causing their loss. However, measurements of low-energy electrons are challenging, and as a result, this population has been somewhat neglected previously. This study concerns observations of low-energy electrons made by the Helium Oxygen Proton Electron instrument on board the Van Allen Probes satellites and also observations from geosynchronous orbit made by the Magnetospheric Plasma Analyzer on board Los Alamos National Laboratory satellites. The fluxes of electrons from ~30 eV to 1 keV are quantified as a function of pitch-angle, McIlwain L parameter, and local time for both quiet and active periods. Results indicate two sources for low-energy electrons in this energy range: the low-energy tail of the electron plasma sheet and the high-energy tail of the dayside ionosphere. These populations are identified primarily as a result of their different pitch-angle distributions. Field-aligned outflows from the dayside ionosphere are observed at all L shells during quiet and active periods. Our results also demonstrate that the dayside electron field-aligned fluxes at ~30 eV are particularly strong between L values of 6 and 7, indicating an enhanced source within the polar ionosphere. Denton, M.; Reeves, G.; Larsen, B.; Friedel, R.; Thomsen, M.; Fernandes, P.; Skoug, R.; Funsten, H.; Sarno-Smith, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA023648 |
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Magnetospheric whistler mode waves are of great importance in the radiation belt electron dynamics. Here on the basis of the analysis of a rare event with the simultaneous disappearances of whistler mode plasmaspheric hiss, exohiss, and chorus triggered by a sudden decrease in the solar wind dynamic pressure, we provide evidences for the following physical scenarios: (1) nonlinear generation of chorus controlled by the geomagnetic field inhomogeneity, (2) origination of plasmaspheric hiss from chorus, and (3) leakage of plasmaspheric hiss into exohiss. Following the reduction of the solar wind dynamic pressure, the dayside geomagnetic field configuration with the enhanced inhomogeneity became unfavorable for the generation of chorus, and the quenching of chorus directly caused the disappearances of plasmaspheric hiss and then exohiss. Liu, Nigang; Su, Zhenpeng; Gao, Zhonglei; Zheng, Huinan; Wang, Yuming; Wang, Shui; Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Funsten, H.; Wygant, J.; Published by: Geophysical Research Letters Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016GL071987 Chorus; Exohiss; Plasmaspheric Hiss; Van Allen Probes; wave disappearance; wave generation |
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Magnetospheric whistler mode waves are of great importance in the radiation belt electron dynamics. Here on the basis of the analysis of a rare event with the simultaneous disappearances of whistler mode plasmaspheric hiss, exohiss, and chorus triggered by a sudden decrease in the solar wind dynamic pressure, we provide evidences for the following physical scenarios: (1) nonlinear generation of chorus controlled by the geomagnetic field inhomogeneity, (2) origination of plasmaspheric hiss from chorus, and (3) leakage of plasmaspheric hiss into exohiss. Following the reduction of the solar wind dynamic pressure, the dayside geomagnetic field configuration with the enhanced inhomogeneity became unfavorable for the generation of chorus, and the quenching of chorus directly caused the disappearances of plasmaspheric hiss and then exohiss. Liu, Nigang; Su, Zhenpeng; Gao, Zhonglei; Zheng, Huinan; Wang, Yuming; Wang, Shui; Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Funsten, H.; Wygant, J.; Published by: Geophysical Research Letters Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016GL071987 Chorus; Exohiss; Plasmaspheric Hiss; Van Allen Probes; wave disappearance; wave generation |
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Magnetospheric whistler mode waves are of great importance in the radiation belt electron dynamics. Here on the basis of the analysis of a rare event with the simultaneous disappearances of whistler mode plasmaspheric hiss, exohiss, and chorus triggered by a sudden decrease in the solar wind dynamic pressure, we provide evidences for the following physical scenarios: (1) nonlinear generation of chorus controlled by the geomagnetic field inhomogeneity, (2) origination of plasmaspheric hiss from chorus, and (3) leakage of plasmaspheric hiss into exohiss. Following the reduction of the solar wind dynamic pressure, the dayside geomagnetic field configuration with the enhanced inhomogeneity became unfavorable for the generation of chorus, and the quenching of chorus directly caused the disappearances of plasmaspheric hiss and then exohiss. Liu, Nigang; Su, Zhenpeng; Gao, Zhonglei; Zheng, Huinan; Wang, Yuming; Wang, Shui; Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Funsten, H.; Wygant, J.; Published by: Geophysical Research Letters Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016GL071987 Chorus; Exohiss; Plasmaspheric Hiss; Van Allen Probes; wave disappearance; wave generation |
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Spectra of keV protons related to ion-cyclotron wave packets We use the Fokker-Planck-Kolmogorov equation to study the statistical aspects of stochastic dynamics of the radiation belt (RB) protons driven by nonlinear electromagnetic ion-cyclotron (EMIC) wave packets. We obtain the spectra of keV protons scattered by these waves that show steeping near the gyroresonance, the signature of resonant wave-particle interaction that cannot be described by a simple power law. The most likely mechanism for proton precipitation events in RBs is shown to be nonlinear wave-particle interaction, namely, the scattering of RB protons into the loss cone by EMIC waves. Khazanov, K.; Sibeck, D.; Tel\textquoterightnikhin, A.; Kronberg, T.; Published by: Physics of Plasmas Published on: 01/2017 YEAR: 2017 DOI: http://dx.doi.org/10.1063/1.4973323 Diffusion; Particle precipitation; protons; Van Allen Probes; wave particle interactions; Wave power |
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An interesting form of \textquotedblleftzipper-like\textquotedblright magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 fcp and fLHR. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. Li, J.; Bortnik, J.; Li, W.; Ma, Q.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Wygant, J.; Breneman, A.; Thaller, S.; Funsten, H.; Mitchell, D.; Manweiler, J.; Torbert, R.; Le Contel, O.; Ergun, R.; Lindqvist, P.-A.; Torkar, K.; Nakamura, R.; Andriopoulou, M.; Russell, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA023536 magnetosonic wave; Radiation belt; rising-tone; Van Allen Probes; zipper-like |
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An interesting form of \textquotedblleftzipper-like\textquotedblright magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 fcp and fLHR. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. Li, J.; Bortnik, J.; Li, W.; Ma, Q.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Wygant, J.; Breneman, A.; Thaller, S.; Funsten, H.; Mitchell, D.; Manweiler, J.; Torbert, R.; Le Contel, O.; Ergun, R.; Lindqvist, P.-A.; Torkar, K.; Nakamura, R.; Andriopoulou, M.; Russell, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA023536 magnetosonic wave; Radiation belt; rising-tone; Van Allen Probes; zipper-like |
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An interesting form of \textquotedblleftzipper-like\textquotedblright magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 fcp and fLHR. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. Li, J.; Bortnik, J.; Li, W.; Ma, Q.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Wygant, J.; Breneman, A.; Thaller, S.; Funsten, H.; Mitchell, D.; Manweiler, J.; Torbert, R.; Le Contel, O.; Ergun, R.; Lindqvist, P.-A.; Torkar, K.; Nakamura, R.; Andriopoulou, M.; Russell, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA023536 magnetosonic wave; Radiation belt; rising-tone; Van Allen Probes; zipper-like |