Bibliography
|
Notice:
|
Found 107 entries in the Bibliography.
Showing entries from 51 through 100
| 2019 |
|
Simultaneous trapping of EMIC and MS waves by background plasmas Electromagnetic ion cyclotron waves and fast magnetosonic waves are found to be simultaneously modulated by background plasma density: both kinds of waves were observed in high plasma density regions but vanished in low density regions. Theoretical analysis based on Snell\textquoterights law and linear growth theory have been utilized to investigate the physical mechanisms driving such modulation. It is suggested that the modulation of fast magnetosonic waves might be due to trapping by plasma density structures, which results from a conservation of the parameter Q during their propagation. Here Q = nrsinψ, with n the refractive index, r the radial distance, and ψ the wave azimuthal angle. As for electromagnetic ion cyclotron waves, the modulation might be owed to the ion composition difference between different plasma density regions. Our results indicate the alternative mechanism for simultaneous appearance of electromagnetic ion cyclotron waves and fast magnetosonic waves (rather than wave excitations of both two wave emissions), which might take combined effects on the evolution of radiation belt electrons. Yuan, Zhigang; Yu, Xiongdong; Ouyang, Zhihai; Yao, Fei; Huang, Shiyong; Funsten, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA026149 EMIC waves; MS waves; Ring current ions; Van Allen Probes; Wave trapping |
|
Simultaneous trapping of EMIC and MS waves by background plasmas Electromagnetic ion cyclotron waves and fast magnetosonic waves are found to be simultaneously modulated by background plasma density: both kinds of waves were observed in high plasma density regions but vanished in low density regions. Theoretical analysis based on Snell\textquoterights law and linear growth theory have been utilized to investigate the physical mechanisms driving such modulation. It is suggested that the modulation of fast magnetosonic waves might be due to trapping by plasma density structures, which results from a conservation of the parameter Q during their propagation. Here Q = nrsinψ, with n the refractive index, r the radial distance, and ψ the wave azimuthal angle. As for electromagnetic ion cyclotron waves, the modulation might be owed to the ion composition difference between different plasma density regions. Our results indicate the alternative mechanism for simultaneous appearance of electromagnetic ion cyclotron waves and fast magnetosonic waves (rather than wave excitations of both two wave emissions), which might take combined effects on the evolution of radiation belt electrons. Yuan, Zhigang; Yu, Xiongdong; Ouyang, Zhihai; Yao, Fei; Huang, Shiyong; Funsten, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA026149 EMIC waves; MS waves; Ring current ions; Van Allen Probes; Wave trapping |
|
To understand the relationship between generation of electromagnetic ion cyclotron (EMIC) waves and energetic particle injections, we performed a statistical study of EMIC waves associated with and without injections based on the Van Allen Probes (Radiation Belt Storm Probes) and Geostationary Operational Environmental Satellite (GOES; GOES-13 and GOES-15) observations. Using 47 months of observations, we identified wave events seen by the Van Allen Probes relative to the plasmapause and to energetic particle injections seen by GOES-13 and GOES-15 on the nightside. We separated the events into four categories: EMIC waves with (without) injections inside (outside) the plasmasphere. We found that He+ EMIC waves have higher occurrence rate inside the plasmasphere, while H+ EMIC waves predominantly occur outside the plasmasphere. Meanwhile, the time duration and peak occurrence rate of EMIC waves associated with injections are shorter and limited to a narrower magnetic local time region than those without injections, indicating that these waves have localized source regions. He+ EMIC waves inside the plasmasphere associated with injection are usually accompanied by an increase in H+ flux within energies of 1\textendash50 keV through all magnetic local time regions, while most wave events outside the plasmasphere show less relationship with H+ flux increase. From these observations, we suggest that injected hot ions are the major driver of He+ EMIC waves inside the plasmasphere during active time. Expanding plasmasphere during quiet times can provide broad wave source regions for He+ EMIC waves on the dayside. However, H+ EMIC waves outside the plasmasphere show different characteristics, suggesting that these waves are generated by other processes. Jun, C.-W.; Yue, C.; Bortnik, J.; Lyons, L.; Nishimura, Y.; Kletzing, C.; Wygant, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA025886 EMIC waves associated with and without injections; Relationship between EMIC wave activity and energetic H+ flux variation; Simultaneous observations using the Van Allen Probes and GOES satellites; Spatial occurrence distributions of EMIC waves; Van Allen Probes |
| 2018 |
|
With observations of Van Allen Probe A, in this letter we display a typical event where banded whistler waves shifted up their frequencies with frequency bands broadening as a response to the enhancement of solar wind dynamic pressure. Meanwhile, the anisotropy of electrons with energies about several tens of keV was observed to increase. Through the comparison of the calculated wave growth rates and observed wave spectral intensity, we suggest that those banded whistler waves observed with frequencies shifted up and frequency bands broadening could be locally excited by these hot electrons with increased anisotropy. The current study provides a great in situ evidence for the influence on frequencies of banded whistler waves by the enhancement of solar wind dynamic pressures, which reveals the important role of solar wind dynamic pressures playing in the frequency properties of banded whistler waves. Yu, Xiongdong; Yuan, Zhigang; Li, Haimeng; Huang, Shiyong; Wang, Dedong; Yao, Fei; Funsten, H.; Wygant, J.; Published by: Geophysical Research Letters Published on: Mar-08-2020 YEAR: 2018 DOI: 10.1029/2018GL078849 Banded whistler-mode waves; Frequency properties; inner magnetosphere; solar wind dynamic pressure; Van Allen Probes |
|
With observations of Van Allen Probe A, in this letter we display a typical event where banded whistler waves shifted up their frequencies with frequency bands broadening as a response to the enhancement of solar wind dynamic pressure. Meanwhile, the anisotropy of electrons with energies about several tens of keV was observed to increase. Through the comparison of the calculated wave growth rates and observed wave spectral intensity, we suggest that those banded whistler waves observed with frequencies shifted up and frequency bands broadening could be locally excited by these hot electrons with increased anisotropy. The current study provides a great in situ evidence for the influence on frequencies of banded whistler waves by the enhancement of solar wind dynamic pressures, which reveals the important role of solar wind dynamic pressures playing in the frequency properties of banded whistler waves. Yu, Xiongdong; Yuan, Zhigang; Li, Haimeng; Huang, Shiyong; Wang, Dedong; Yao, Fei; Funsten, H.; Wygant, J.; Published by: Geophysical Research Letters Published on: Mar-08-2020 YEAR: 2018 DOI: 10.1029/2018GL078849 Banded whistler-mode waves; Frequency properties; inner magnetosphere; solar wind dynamic pressure; Van Allen Probes |
|
In this letter, we present unique conjugated satellite observations of MeV relativistic electron precipitation caused by electromagnetic ion cyclotron (EMIC) waves. On the outer boundary of the plasmasphere, the Van Allen probe observed EMIC waves. At ionospheric altitudes, the NOAA 16 satellite at the footprint of Van Allen probe simultaneously detected obvious flux enhancements for precipitating >MeV radiation belt electrons, but not for precipitating Yuan, Zhigang; Liu, Kun; Yu, Xiongdong; Yao, Fei; Huang, Shiyong; Wang, Dedong; Ouyang, Zhihai; Published by: Geophysical Research Letters Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018GL080481 Chorus; EMIC waves; Particle precipitation; Radiation belt; ring current; Van Allen Probes; Wave-particle interaction |
|
In this letter, we present unique conjugated satellite observations of MeV relativistic electron precipitation caused by electromagnetic ion cyclotron (EMIC) waves. On the outer boundary of the plasmasphere, the Van Allen probe observed EMIC waves. At ionospheric altitudes, the NOAA 16 satellite at the footprint of Van Allen probe simultaneously detected obvious flux enhancements for precipitating >MeV radiation belt electrons, but not for precipitating Yuan, Zhigang; Liu, Kun; Yu, Xiongdong; Yao, Fei; Huang, Shiyong; Wang, Dedong; Ouyang, Zhihai; Published by: Geophysical Research Letters Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018GL080481 Chorus; EMIC waves; Particle precipitation; Radiation belt; ring current; Van Allen Probes; Wave-particle interaction |
|
Generation of EMIC Waves Observed by Van Allen Probes at Low L Shells 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 of velocity. (2) The timing and frequencies of generated waves are in agreement with observations. The generated wave normal angles, however, are highly oblique being in strong disagreement with the minimum variance angles obtained from Fast Fourier transform. (3) The wave step analysis shows that a signal nonstationarity is not a major cause for disagreement between the minimum variance angles and theoretical predictions for normal angles. (4) A superposition of plane sine waves with the same frequency and normal angle but with different azimuthal angles for wave vector around the background magnetic field can reconcile the polarization properties of EMIC waves obtained from Fast Fourier transform and/or the wave step analysis with those predicted by the linear theory of EMIC waves. Gamayunov, Konstantin; Min, Kyungguk; Saikin, Anthony; Rassoul, Hamid; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2018JA025629 effects of wave superposition on EMIC waves; EMIC wave generation; EMIC waves at low L shells; growth rate calculations for EMIC waves; polarization properties of EMIC waves; Van Allen Probes; Van Allen Probes observations at low L shells |
|
Using the Van Allen Probe A observations, we obtained the global distribution of proton rings and calculated the linear wave growth rate of fast magnetosonic (MS) waves in the region L ~ 3-6. Our statistical and calculated results demonstrate that MS waves can be locally excited on the dayside outside the plasmapause, as well as in the dusk sector inside the plasmapause. The frequency range of unstable MS waves is strongly modulated by the ratio of the proton ring velocity (Vr) to the local Alfv\ en speed (VA). High harmonic MS waves (ω>20ΩH+) can be excited outside the plasmapause where Vr/VA<1 while low harmonic MS waves (ω<10ΩH+) with frequencies less than ~30 Hz are found to be excited both outside and inside the plasmapause where 1 Yuan, Zhigang; Ouyang, Zhihai; Yu, Xiongdong; Huang, Shiyong; Yao, Fei; Funsten, H.; Published by: Geophysical Research Letters Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018GL079999 Fast Magnetosonic Waves; linear growth rates; locally excited; low harmonic magnetosonic waves; Proton rings; Van Allen Probes |
|
Using the Van Allen Probe A observations, we obtained the global distribution of proton rings and calculated the linear wave growth rate of fast magnetosonic (MS) waves in the region L ~ 3-6. Our statistical and calculated results demonstrate that MS waves can be locally excited on the dayside outside the plasmapause, as well as in the dusk sector inside the plasmapause. The frequency range of unstable MS waves is strongly modulated by the ratio of the proton ring velocity (Vr) to the local Alfv\ en speed (VA). High harmonic MS waves (ω>20ΩH+) can be excited outside the plasmapause where Vr/VA<1 while low harmonic MS waves (ω<10ΩH+) with frequencies less than ~30 Hz are found to be excited both outside and inside the plasmapause where 1 Yuan, Zhigang; Ouyang, Zhihai; Yu, Xiongdong; Huang, Shiyong; Yao, Fei; Funsten, H.; Published by: Geophysical Research Letters Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018GL079999 Fast Magnetosonic Waves; linear growth rates; locally excited; low harmonic magnetosonic waves; Proton rings; Van Allen Probes |
|
The composition of plasma inside geostationary orbit based on Van Allen Probes observations The composition of the inner magnetosphere is of great importance for determining the plasma pressure, and thus the currents and magnetic field configuration. In this study, we perform a statistical survey of equatorial plasma pressure distributions and investigate the relative contributions of ions and electron with different energies inside of geostationary orbit under two AE levels based on over sixty months of observations from the HOPE and RBSPICE mass spectrometers on board Van Allen Probes. We find that the total and partial pressures of different species increase significantly at high AE levels with Hydrogen (H+) pressure being dominant in the plasmasphere. The pressures of the heavy ions and electrons increase outside the plasmapause and develop a strong dawn-dusk asymmetry with ion pressures peaking at dusk and electron pressure peaking at dawn. In addition, ring current H+ with energies ranging from 50 keV up to several hundred keV is the dominant component of plasma pressure during both quiet (> 90\%) and active times (> 60\%), while Oxygen (O+) with 10 < E < 50 keV and electrons with 0.1 < E < 40 keV become important during active times contributing more than 25\% and 20\% on the nightside, respectively, while the Helium (He+) contribution is generally small. The results presented in this study provide a global picture of the equatorial plasma pressure distributions and the associated contributions from different species with different energy ranges, which advance our knowledge of wave generation and provide models with a systematic baseline of plasma composition. Yue, Chao; Bortnik, Jacob; Li, Wen; Ma, Qianli; Gkioulidou, Matina; Reeves, Geoffrey; Wang, Chih-Ping; Thorne, Richard; T. Y. Lui, Anthony; Gerrard, Andrew; Spence, Harlan; Mitchell, Donald; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018JA025344 ion composition; plasma pressure; Plasmapause; Van Allen Probes |
|
Cold Ion Heating by Magnetosonic Waves in a Density Cavity of the Plasmasphere Fast magnetosonic (MS) waves play an important role in the dynamics of the inner magnetosphere. Theoretical prediction and simulation have demonstrated that MS waves can heat cold ions. However, direct observational evidence of cold ion heating by MS waves has so far remained elusive. In this paper, we show a typical event of cold ion heating by magnetosonic waves in a density cavity of the plasmasphere with observations of the Van Allen Probe mission on 22 August 2013. During enhancements of the MS wave intensity in the density cavity, the fluxes of trapped H+ and He+ ions with energies of 10\textendash100 eV were observed to increase, implying that cold plasmaspheric ions were heated through high-order resonances with the MS waves. Based on simultaneous observations of ring current protons, we have calculated local linear growth rates, which demonstrate that magnetosonic waves can be locally generated in the density cavity. Our results provide a direct observational proof of the energy coupling process between the ring current and plasmasphere; that is, through exciting MS waves, the free energy stored in the ring current protons with ring distributions is released. In the density cavity of the plasmasphere, both cold H+ and He+ ions are heated by MS waves. As a result, the energy of the ring current can be transferred into the plasmasphere Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Qiao, Zheng; Yao, Fei; Funsten, Herbert; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2018 YEAR: 2018 DOI: 10.1002/2017JA024919 cold ion heating; Density cavities; local linear growth rates; magnetosonic waves; Ring current ions; Van Allen Probes; \textquoteleftring\textquoteright distributions |
|
Cold Ion Heating by Magnetosonic Waves in a Density Cavity of the Plasmasphere Fast magnetosonic (MS) waves play an important role in the dynamics of the inner magnetosphere. Theoretical prediction and simulation have demonstrated that MS waves can heat cold ions. However, direct observational evidence of cold ion heating by MS waves has so far remained elusive. In this paper, we show a typical event of cold ion heating by magnetosonic waves in a density cavity of the plasmasphere with observations of the Van Allen Probe mission on 22 August 2013. During enhancements of the MS wave intensity in the density cavity, the fluxes of trapped H+ and He+ ions with energies of 10\textendash100 eV were observed to increase, implying that cold plasmaspheric ions were heated through high-order resonances with the MS waves. Based on simultaneous observations of ring current protons, we have calculated local linear growth rates, which demonstrate that magnetosonic waves can be locally generated in the density cavity. Our results provide a direct observational proof of the energy coupling process between the ring current and plasmasphere; that is, through exciting MS waves, the free energy stored in the ring current protons with ring distributions is released. In the density cavity of the plasmasphere, both cold H+ and He+ ions are heated by MS waves. As a result, the energy of the ring current can be transferred into the plasmasphere Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Qiao, Zheng; Yao, Fei; Funsten, Herbert; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2018 YEAR: 2018 DOI: 10.1002/2017JA024919 cold ion heating; Density cavities; local linear growth rates; magnetosonic waves; Ring current ions; Van Allen Probes; \textquoteleftring\textquoteright distributions |
|
A typical case of electromagnetic ion cyclotron (EMIC) emissions with both He+ band and O+ band waves was observed by Van Allen Probe A on 14 July 2014. These emissions occurred in the morning sector on the equator inside the plasmasphere, in which region O+ band EMIC waves prefer to appear. Through property analysis of these emissions, it is found that the He+ band EMIC waves are linearly polarized and propagating quasi-parallelly along the background magnetic field, while the O+ band ones are of linear and left-hand polarization and propagating obliquely with respect to the background magnetic field. Using the in situ observations of plasma environment and particle data, excitation of these O+ band EMIC waves has been investigated with the linear growth theory. The calculated linear growth rate shows that these O+ band EMIC waves can be locally excited by ring current protons with ring velocity distributions. The comparison of the observed wave spectral intensity and the calculated growth rate suggests that the density of H+ rings providing the free energy for the instability has decreased after the wave grows. Therefore, this paper provides a direct observational evidence to the excitation mechanism of O+ band EMIC waves: ring current protons with ring distributions provide the free energy supporting the instability in the presence of rich O+ in the plasmasphere. Yu, Xiongdong; Yuan, Zhigang; Huang, Shiyong; Yao, Fei; Wang, Dedong; Funsten, Herbert; Wygant, John; Published by: Geophysical Research Letters Published on: 02/2018 YEAR: 2018 DOI: 10.1002/grl.v45.310.1002/2018GL077109 linear wave growth; O+ band EMIC waves; ring distributions; Van Allen Probes |
|
A typical case of electromagnetic ion cyclotron (EMIC) emissions with both He+ band and O+ band waves was observed by Van Allen Probe A on 14 July 2014. These emissions occurred in the morning sector on the equator inside the plasmasphere, in which region O+ band EMIC waves prefer to appear. Through property analysis of these emissions, it is found that the He+ band EMIC waves are linearly polarized and propagating quasi-parallelly along the background magnetic field, while the O+ band ones are of linear and left-hand polarization and propagating obliquely with respect to the background magnetic field. Using the in situ observations of plasma environment and particle data, excitation of these O+ band EMIC waves has been investigated with the linear growth theory. The calculated linear growth rate shows that these O+ band EMIC waves can be locally excited by ring current protons with ring velocity distributions. The comparison of the observed wave spectral intensity and the calculated growth rate suggests that the density of H+ rings providing the free energy for the instability has decreased after the wave grows. Therefore, this paper provides a direct observational evidence to the excitation mechanism of O+ band EMIC waves: ring current protons with ring distributions provide the free energy supporting the instability in the presence of rich O+ in the plasmasphere. Yu, Xiongdong; Yuan, Zhigang; Huang, Shiyong; Yao, Fei; Wang, Dedong; Funsten, Herbert; Wygant, John; Published by: Geophysical Research Letters Published on: 02/2018 YEAR: 2018 DOI: 10.1002/grl.v45.310.1002/2018GL077109 linear wave growth; O+ band EMIC waves; ring distributions; Van Allen Probes |
|
Based on the wave and proton observations by Van Allen Probes A and B, we examined the effects of hot protons (0.01\textendash50 keV) on fast magnetosonic (MS) waves inside and outside the Earth\textquoterights plasmasphere. In the low-density plasma trough outside the plasmapause, the gyroresonance interactions between hot protons and MS waves not only cause the MS wave growth at some frequencies but also lead to the damping of MS waves at other frequencies, which depends on the proton phase space density gradient and the ambient plasma density. The gyroresonance of the observed hot protons cannot excite MS waves near the lower hybrid resonance frequency and even causes the MS wave damping. Thus, the frequencies of the observed MS waves outside the plasmapause are usually lower than the lower hybrid resonance frequency. In the high-density plasmasphere, the observed hot protons merely lead to the weak gyrodamping of MS waves. The persistent existence of lower band MS waves indicates that the weak gyrodamping effect of hot protons on MS waves is ignorable in the high-density plasmasphere. Liu, Bin; Li, Liuyuan; Yu, Jiang; Cao, Jinbin; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2018 YEAR: 2018 DOI: 10.1002/2017JA024676 damping of magnetosonic waves; growth of magnetosonic waves; magnetosonic waves; magnetospheric hot protons; Van Allen Probes; wave-particle interactions |
| 2017 |
|
A neural network model of three-dimensional dynamic electron density in the inner magnetosphere A plasma density model of the inner magnetosphere is important for a variety of applications including the study of wave-particle interactions, and wave excitation and propagation. Previous empirical models have been developed under many limiting assumptions and do not resolve short-term variations, which are especially important during storms. We present a three-dimensional dynamic electron density (DEN3D) model developed using a feedforward neural network with electron densities obtained from four satellite missions. The DEN3D model takes spacecraft location and time series of solar and geomagnetic indices (F10.7, SYM-H, and AL) as inputs. It can reproduce the observed density with a correlation coefficient of 0.95 and predict test data set with error less than a factor of 2. Its predictive ability on out-of-sample data is tested on field-aligned density profiles from the IMAGE satellite. DEN3D\textquoterights predictive ability provides unprecedented opportunities to gain insight into the 3-D behavior of the inner magnetospheric plasma density at any time and location. As an example, we apply DEN3D to a storm that occurred on 1 June 2013. It successfully reproduces various well-known dynamic features in three dimensions, such as plasmaspheric erosion and recovery, as well as plume formation. Storm time long-term density variations are consistent with expectations; short-term variations appear to be modulated by substorm activity or enhanced convection, an effect that requires further study together with multispacecraft in situ or imaging measurements. Investigating plasmaspheric refilling with the model, we find that it is not monotonic in time and is more complex than expected from previous studies, deserving further attention. Chu, X.; Bortnik, J.; Li, W.; Ma, Q.; Denton, R.; Yue, C.; Angelopoulos, V.; Thorne, R.; Darrouzet, F.; Ozhogin, P.; Kletzing, C.; Wang, Y.; Menietti, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA024464 |
|
The characteristic response of whistler mode waves to interplanetary shocks Magnetospheric whistler mode waves play a key role in regulating the dynamics of the electron radiation belts. Recent satellite observations indicate a significant influence of interplanetary (IP) shocks on whistler mode wave power in the inner magnetosphere. In this study, we statistically investigate the response of whistler mode chorus and plasmaspheric hiss to IP shocks based on Van Allen Probes and THEMIS satellite observations. Immediately after the IP shock arrival, chorus wave power is usually intensified, often at post-midnight to pre-noon sector, while plasmaspheric hiss wave power predominantly decreases near the dayside but intensifies near the nightside. We conclude that chorus wave intensification outside the plasmasphere is probably associated with the suprathermal electron flux enhancement caused by the IP shock. Through a simple ray tracing modeling assuming the scenario that plasmaspheric hiss is originated from chorus, we find that the solar wind dynamic pressure increase changes the magnetic field configuration to favor ray penetration in the nightside and promote ray refraction away from the dayside, potentially explaining the magnetic local time (MLT) dependent responses of plasmaspheric hiss waves following IP shock arrivals. Yue, Chao; Chen, Lunjin; Bortnik, Jacob; Ma, Qianli; Thorne, Richard; Angelopoulos, Vassilis; Li, Jinxing; An, Xin; Zhou, Chen; Kletzing, Craig; Reeves, Geoffrey; Spence, Harlan; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA024574 IP shocks; MLT dependent; Plasmaspheric Hiss; Ray Tracing; Van Allen Probes; whistler mode chorus |
|
We report observational evidence of cold plamsmaspheric electron (< 200 eV) acceleration by ultra-low-frequency (ULF) waves in the plasmaspheric boundary layer on 10 September 2015. Strongly enhanced cold electron fluxes in the energy spectrogram were observed along with second harmonic mode waves with a period of about 1 minute which lasted several hours during two consecutive Van Allen Probe B orbits. Cold electron (<200 eV) and energetic proton (10-20 keV) bi-directional pitch angle signatures observed during the event are suggestive of the drift-bounce resonance mechanism. The correlation between enhanced energy fluxes and ULF waves leads to the conclusions that plasmaspheric dynamics is strongly affected by ULF waves. Van Allen Probe A and B, GOES 13, GOES 15 and MMS 1 observations suggest ULF waves in the event were strongest on the dusk-side magnetosphere. Measurements from MMS 1 contain no evidence of an external wave source during the period when ULF waves and injected energetic protons with a bump-on-tail distribution were detected by Van Allen Probe B. This suggests that the observed ULF waves were probably excited by a localized drift-bounce resonant instability, with the free energy supplied by substorm-injected energetic protons. The observations by Van Allen Probe B suggest that energy transfer between particle species in different energy ranges can take place through the action of ULF waves, demonstrating the important role of these waves in the dynamical processes of the inner magnetosphere. Ren, Jie; Zong, Q.; Miyoshi, Y.; Zhou, X.; Wang, Y.; Rankin, R.; Yue, C.; Spence, H.; Funsten, H.; Wygant, J.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024316 Cold plasmaspheric electrons; drift-bounce resonance; Plasma instability; Plasmaspheric boundary layer; Substorm-injected protons; ULF waves; Van Allen Probes |
|
Understanding the source and loss processes of various plasma populations is greatly aided by having accurate knowledge of their pitch angle distributions (PADs). Here, we statistically analyze ~1 eV to 600 keV hydrogen (H+) PADs near the geomagnetic equator in the inner magnetosphere based on Van Allen Probes measurements, to comprehensively investigate how the H+ PADs vary with different energies, magnetic local times (MLTs), L-shells, and geomagnetic conditions. Our survey clearly indicates four distinct populations with different PADs: (1) a pancake distribution of the plasmaspheric H+ at low L-shells except for dawn sector; (2) a bi-directional field-aligned distribution of the warm plasma cloak; (3) pancake or isotropic distributions of ring current H+; (4) radiation belt particles show pancake, butterfly and isotropic distributions depending on their energy, MLT and L-shell. Meanwhile, the pancake distribution of ring current H+ moves to lower energies as L-shell increases which is primarily caused by adiabatic transport. Furthermore, energetic H+ (> 10 keV) PADs become more isotropic following the substorm injections, indicating wave-particle interactions. The radiation belt H+ butterfly distributions are identified in a narrow energy range of 100 < E < 400 keV at large L (L > 5), which are less significant during quiet times and extend from dusk to dawn sector through midnight during substorms. The different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations. Yue, Chao; Bortnik, Jacob; Thorne, Richard; Ma, Qianli; An, Xin; Chappell, C.; Gerrard, Andrew; Lanzerotti, Louis; Shi, Quanqi; Reeves, Geoffrey; Spence, Harlan; Mitchell, Donald; Gkioulidou, Matina; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024421 bi-directional field-aligned; H+ Pitch angle distributions; plasmaspheric H+; radiation belt H+; ring current; Van Allen Probes; warm Plasma cloak |
|
EMIC waves covering wide L shells: MMS and Van Allen Probes observations During 04:45:00\textendash08:15:00 UT on 13 September in 2015, a case of Electromagnetic ion cyclotron (EMIC) waves covering wide L shells (L = 3.6\textendash9.4), observed by the Magnotospheric Multiscale 1 (MMS1) are reported. During the same time interval, EMIC waves observed by Van Allen Probes A (VAP-A) only occurred just outside the plasmapause. As the Van Allen Probes moved outside into a more tenuous plasma region, no intense waves were observed. Combined observations of MMS1 and VAP-A suggest that in the terrestrial magnetosphere, an appropriately dense background plasma would make contributions to the growth of EMIC waves in lower L shells, while the ion anisotropy, driven by magnetospheric compression, might play an important role in the excitation of EMIC waves in higher L shells. These EMIC waves are observed over wide L shells after three continuous magnetic storms, which suggests that these waves might obtain their free energy from those energetic ions injected during storm times. These EMIC waves should be included in radiation belt modeling, especially during continuous magnetic storms. Moreover, two-band structures separated in frequencies by local He2+ gyrofrequencies were observed in large L shells (L > ~6), implying sufficiently rich solar wind origin He2+ likely in the outer ring current. It is suggested that multiband-structured EMIC waves can be used to trace the coupling between solar wind and the magnetosphere. Yu, Xiongdong; Yuan, Zhigang; Huang, Shiyong; Wang, Dedong; Li, Haimeng; Qiao, Zheng; Yao, Fei; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2017JA023982 EMIC waves; MMS; solar wind dynamic pressure; Van Allen Probes |
|
EMIC waves covering wide L shells: MMS and Van Allen Probes observations During 04:45:00\textendash08:15:00 UT on 13 September in 2015, a case of Electromagnetic ion cyclotron (EMIC) waves covering wide L shells (L = 3.6\textendash9.4), observed by the Magnotospheric Multiscale 1 (MMS1) are reported. During the same time interval, EMIC waves observed by Van Allen Probes A (VAP-A) only occurred just outside the plasmapause. As the Van Allen Probes moved outside into a more tenuous plasma region, no intense waves were observed. Combined observations of MMS1 and VAP-A suggest that in the terrestrial magnetosphere, an appropriately dense background plasma would make contributions to the growth of EMIC waves in lower L shells, while the ion anisotropy, driven by magnetospheric compression, might play an important role in the excitation of EMIC waves in higher L shells. These EMIC waves are observed over wide L shells after three continuous magnetic storms, which suggests that these waves might obtain their free energy from those energetic ions injected during storm times. These EMIC waves should be included in radiation belt modeling, especially during continuous magnetic storms. Moreover, two-band structures separated in frequencies by local He2+ gyrofrequencies were observed in large L shells (L > ~6), implying sufficiently rich solar wind origin He2+ likely in the outer ring current. It is suggested that multiband-structured EMIC waves can be used to trace the coupling between solar wind and the magnetosphere. Yu, Xiongdong; Yuan, Zhigang; Huang, Shiyong; Wang, Dedong; Li, Haimeng; Qiao, Zheng; Yao, Fei; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2017JA023982 EMIC waves; MMS; solar wind dynamic pressure; Van Allen Probes |
|
In situ observations of magnetosonic waves modulated by background plasma density We report in situ observations by the Van Allen Probe mission that magnetosonic (MS) waves are clearly relevant to appear relevant to the background plasma number density. As the satellite moved across dense and tenuous plasma alternatively, MS waves occurred only in lower density region. As the observed protons with \textquoteleftring\textquoteright distributions provide free energy, local linear growth rates are calculated and show that magnetosonic waves can be locally excited in tenuous plasma. With variations of the background plasma density, the temporal variations of local wave growth rates calculated with the observed proton ring distributions, show a remarkable agreement with those of the observed wave amplitude. Therefore, the paper provides a direct proof that background plasma densities can modulate the amplitudes of magnetosonic waves through controlling the wave growth rates. Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Wang, Dedong; Funsten, Herbert; Published by: Geophysical Research Letters Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2017GL074681 \textquoterightring\textquoteright distributions; local linear growth rates; magnetosonic waves; Ring current ions; Van Allen Probes |
|
In situ observations of magnetosonic waves modulated by background plasma density We report in situ observations by the Van Allen Probe mission that magnetosonic (MS) waves are clearly relevant to appear relevant to the background plasma number density. As the satellite moved across dense and tenuous plasma alternatively, MS waves occurred only in lower density region. As the observed protons with \textquoteleftring\textquoteright distributions provide free energy, local linear growth rates are calculated and show that magnetosonic waves can be locally excited in tenuous plasma. With variations of the background plasma density, the temporal variations of local wave growth rates calculated with the observed proton ring distributions, show a remarkable agreement with those of the observed wave amplitude. Therefore, the paper provides a direct proof that background plasma densities can modulate the amplitudes of magnetosonic waves through controlling the wave growth rates. Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Wang, Dedong; Funsten, Herbert; Published by: Geophysical Research Letters Published on: 07/2017 YEAR: 2017 DOI: 10.1002/2017GL074681 \textquoterightring\textquoteright distributions; local linear growth rates; magnetosonic waves; Ring current ions; Van Allen Probes |
|
Using multisatellite measurements, a uniquely strong and long-lived relativistic electron slot region refilling event from November 2004 to January 2005 is investigated. This event occurred under remarkable interplanetary and magnetospheric conditions. Both empirically modeled and observationally estimated plasmapause locations demonstrate that the plasmasphere eroded significantly prior to the enhancement phase of this event. The estimated diffusion coefficients indicate that the radial diffusion due to ULF waves is insufficient to account for the observed enhancement of slot region electrons. However, the diffusion coefficients evaluated using the distribution of chorus wave intensities derived from low-altitude POES electron observations indicate that the local acceleration induced by chorus could account for the major feature of observed enhancement outside the plasmapause. When the plasmasphere recovered, the refilled slot region was enveloped inside the plasmapause. In the plasmasphere, while the efficiency of hiss scattering loss increases by including unusually low frequency hiss waves, the interaction with hiss alone cannot fully explain the decay of this event, especially at higher energies, which suggests that electromagnetic ion cyclotron waves contribute to the relativistic electron loss process at such low L shells for this refilling event. Through a comprehensive analysis on the basis of data analyses and numerical calculations, the present study sheds light on the underlying physics responsible for the unusual slot refilling by relativistic electrons, which exhibits the complexity of both radiation belt electron dynamics and associated wave-particle interactions. Yang, Xiaochao; Ni, Binbin; Yu, Jiang; Zhang, Yang; Zhang, Xiaoxin; Sun, Yueqiang; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2017 YEAR: 2017 DOI: 10.1002/2016JA023204 Radiation belt; Relativistic electron; Slot region; Van Allen Probes |
|
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 |
|
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 |
|
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 |
|
Using two-hour (from 2300 UT January 25, 2013 to 0100 UT January 26, 2013) measurement data from Van Allen Probes on fluxes of energetic particles, cold plasma density, and magnetic field magnitude, we have calculated the local growth rate of electromagnetic ion\textendashcyclotron and whistler-mode waves for field-aligned propagation. The results of these calculations have been compared with wave spectra observed by the same Van Allen Probe spacecraft. The time intervals when the calculated wave increments are sufficiently large, and the frequency ranges corresponding to the enhancement peak agree with the frequency\textendashtime characteristics of observed electromagnetic waves. We have analyzed the influence of variations in the density and ionic composition of cold plasma, fluxes of energetic particles, and their pitch-angle distribution on the wave generation. The ducted propagation of waves plays an important role in their generation during the given event. The chorus VLF emissions observed in this event cannot be explained by kinetic cyclotron instability, and their generation requires much sharper changes (\textquotedblleftsteps\textquotedblright) for velocity distributions than those measured by energetic particle detectors on Van Allen Probes satellites. Lyubchich, A.; Demekhov, A.; Titova, E.; Yahnin, A.; Published by: Geomagnetism and Aeronomy Published on: 02/2017 YEAR: 2017 DOI: 10.1134/S001679321701008X |
|
Transitional behavior of different energy protons based on Van Allen Probes observations Understanding the dynamical behavior of ~1 eV to 50 keV ions and identifying the energies at which the morphologies transit are important in that they involve the relative intensities and distributions of the large-scale electric and magnetic fields, the outflow, and recombination rates. However, there have been only few direct observational investigations of the transition in drift behaviors of different energy ions before the Van Allen Probes era. Here we statistically analyze ~1 eV to 50 keV hydrogen (H+) differential flux distributions near geomagnetic equator by using Van Allen Probes observations to investigate the H+ dynamics under the regulation of large-scale electric and magnetic fields. Our survey clearly indicates three types of H+ behaviors within different energy ranges, which is consistent with previous theory predictions. Using simple electric and magnetic field models in UBK coordinates, we have further constrained the source regions of different energy ions and their drift directions. Yue, Chao; Bortnik, Jacob; Chen, Lunjin; Ma, Qianli; Thorne, Richard; Reeves, Geoffrey; Spence, Harlan; Published by: Geophysical Research Letters Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016GL071324 |
| 2016 |
|
Transitional behavior of different energy protons based on Van Allen Probes observations Understanding the dynamical behavior of ~1 eV to 50 keV ions and identifying the energies at which the morphologies transit are important in that they involve the relative intensities and distributions of the large-scale electric and magnetic fields, the outflow and recombination rates. However, there have been only few direct observational investigations of the transition in drift behaviors of different energy ions before the Van Allen Probes era. Here, we statistically analyze ~1 eV to 50 keV Hydrogen (H+) differential flux distributions near geomagnetic equator by using Van Allen Probes observations to investigate the H+ dynamics under the regulation of large-scale electric and magnetic fields. Our survey clearly indicates three types of H+ behaviors within different energy ranges, which is consistent with previous theory predictions. Using simple electric and magnetic field models in UBK coordinates, we have further constrained the source regions of different energy ions and their drift directions. Yue, Chao; Bortnik, Jacob; Chen, Lunjin; Ma, Qianli; Thorne, Richard; Reeves, Geoffrey; Spence, Harlan; Published by: Geophysical Research Letters Published on: 12/2016 YEAR: 2016 DOI: 10.1002/2016GL071324 |
|
Ring Current Pressure Estimation with RAM-SCB using Data Assimilation and Van Allen Probe Flux Data Capturing and subsequently modeling the influence of tail plasma injections on the inner magnetosphere is important for understanding the formation and evolution of the ring current. In this study, the ring current distribution is estimated with the Ring Current-Atmosphere Interactions Model with Self-Consistent Magnetic field (RAM-SCB) using, for the first time, data assimilation techniques and particle flux data from the Van Allen Probes. The state of the ring current within the RAM-SCB model is corrected via an ensemble based data assimilation technique by using proton flux from one of the Van Allen Probes, to capture the enhancement of the ring current following an isolated substorm event on July 18, 2013. The results show significant improvement in the estimation of the ring current particle distributions in the RAM-SCB model, leading to better agreement with observations. This newly implemented data assimilation technique in the global modeling of the ring current thus provides a promising tool to improve the characterization of particle distribution in the near-Earth regions. Godinez, Humberto; Yu, Yiqun; Lawrence, Eric; Henderson, Michael; Larsen, Brian; Jordanova, Vania; Published by: Geophysical Research Letters Published on: 11/2016 YEAR: 2016 DOI: 10.1002/2016GL071646 |
|
Electron precipitation down to the atmosphere due to wave-particle scattering in the magnetosphere contributes significantly to the auroral ionospheric conductivity. In order to obtain the auroral conductivity in global MHD models that are incapable of capturing kinetic physics in the magnetosphere, MHD parameters are often used to estimate electron precipitation flux for the conductivity calculation. Such an MHD approach, however, lacks self-consistency in representing the magnetosphere-ionosphere coupling processes. In this study we improve the coupling processes in global models with a more physical method. We calculate the physics-based electron precipitation from the ring current and map it to the ionospheric altitude for solving the ionospheric electrodynamics. In particular, we use the BATS-R-US (Block Adaptive Tree Scheme-Roe type-Upstream) MHD model coupled with the kinetic ring current model RAM-SCB (Ring current-Atmosphere interaction Model with Self-Consistent Magnetic field (B)) that solves pitch angle-dependent electron distribution functions, to study the global circulation dynamics during the 25\textendash26 January 2013 storm event. Since the electron precipitation loss is mostly governed by wave-particle resonant scattering in the magnetosphere, we further investigate two loss methods of specifying electron precipitation loss associated with wave-particle interactions: (1) using pitch angle diffusion coefficients Dαα(E,α) determined from the quasi-linear theory, with wave spectral and plasma density obtained from statistical observations (named as \textquotedblleftdiffusion coefficient method\textquotedblright) and (2) using electron lifetimes τ(E) independent on pitch angles inferred from the above diffusion coefficients (named as \textquotedblleftlifetime method\textquotedblright). We found that both loss methods demonstrate similar temporal evolution of the trapped ring current electrons, indicating that the impact of using different kinds of loss rates is small on the trapped electron population. However, for the precipitated electrons, the lifetime method hardly captures any precipitation in the large L shell (i.e., 4 < L < 6.5) region, while the diffusion coefficient method produces much better agreement with NOAA/POES measurements, including the spatial distribution and temporal evolution of electron precipitation in the region from the premidnight through the dawn to the dayside. Further comparisons of the precipitation energy flux to DMSP observations indicates that the new physics-based precipitation approach using diffusion coefficients for the ring current electron loss can explain the diffuse electron precipitation in the dawn sector, such as the enhanced precipitation flux at auroral latitudes and flux drop near the subauroral latitudes, but the traditional MHD approach largely overestimates the precipitation flux at lower latitudes. Yu, Yiqun; Jordanova, Vania; Ridley, Aaron; Albert, Jay; Horne, Richard; Jeffery, Christopher; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2016 YEAR: 2016 DOI: 10.1002/2016JA022585 Diffusion Coefficient; electron lifetime; electron precipitation; ionospheric conductivity; MI coupling; Van Allen Probes; wave-particle interactions |
|
Plasma kinetic theory predicts that a sufficiently anisotropic electron distribution will excite whistler mode waves, which in turn relax the electron distribution in such a way as to create an upper bound on the relaxed electron anisotropy. Here using whistler mode chorus wave and plasma measurements by Van Allen Probes, we confirm that the electron distributions are well constrained by this instability to a marginally stable state in the whistler mode chorus waves generation region. Lower band chorus waves are organized by the electron β||e into two distinct groups: (i) relatively large-amplitude, quasi-parallel waves with inline image and (ii) relatively small-amplitude, oblique waves with inline image. The upper band chorus waves also have enhanced amplitudes close to the instability threshold, with large-amplitude waves being quasi-parallel whereas small-amplitude waves being oblique. These results provide important insight for studying the excitation of whistler mode chorus waves. Yue, Chao; An, Xin; Bortnik, Jacob; Ma, Qianli; Li, Wen; Thorne, Richard; Reeves, Geoffrey; Gkioulidou, Matina; Mitchell, Donald; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 08/2016 YEAR: 2016 DOI: 10.1002/2016GL070084 beta parallel; electron temperature anisotropy; marginally stable state; oblique waves; quasi-parallel waves; Van Allen Probes; whistler mode chorus waves |
|
In situ evidence of the modification of the parallel propagation of EMIC waves by heated He + ions With observations of the Van Allen Probe B, we report in situ evidence of the modification of the parallel propagating electromagnetic ion cyclotron (EMIC) waves by heated He+ ions. In the outer boundary of the plasmasphere, accompanied with the He+ ion heating, the frequency bands of H+ and He+ for EMIC waves merged into each other, leading to the disappearance of a usual stop band between the gyrofrequency of He+ ions (ΩHe+) and the H+ cutoff frequency (ωH+co) in the cold plasma. Moreover, the dispersion relation for EMIC waves theoretically calculated with the observed plasma parameters also demonstrates that EMIC waves can indeed parallel propagate across ΩHe+. Therefore, the paper provides an in situ evidence of the modification of the parallel propagation of EMIC waves by heated He+ ions Yuan, Zhigang; Yu, Xiongdong; Wang, Dedong; Huang, Shiyong; Li, Haimeng; Yu, Tao; Qiao, Zheng; Wygant, John; Funsten, Herbert; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2016 YEAR: 2016 DOI: 10.1002/2016JA022573 EMIC waves; He+ ion heating; Ring current ions; stop band; Van Allen Probes |
|
In situ evidence of the modification of the parallel propagation of EMIC waves by heated He + ions With observations of the Van Allen Probe B, we report in situ evidence of the modification of the parallel propagating electromagnetic ion cyclotron (EMIC) waves by heated He+ ions. In the outer boundary of the plasmasphere, accompanied with the He+ ion heating, the frequency bands of H+ and He+ for EMIC waves merged into each other, leading to the disappearance of a usual stop band between the gyrofrequency of He+ ions (ΩHe+) and the H+ cutoff frequency (ωH+co) in the cold plasma. Moreover, the dispersion relation for EMIC waves theoretically calculated with the observed plasma parameters also demonstrates that EMIC waves can indeed parallel propagate across ΩHe+. Therefore, the paper provides an in situ evidence of the modification of the parallel propagation of EMIC waves by heated He+ ions Yuan, Zhigang; Yu, Xiongdong; Wang, Dedong; Huang, Shiyong; Li, Haimeng; Yu, Tao; Qiao, Zheng; Wygant, John; Funsten, Herbert; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2016 YEAR: 2016 DOI: 10.1002/2016JA022573 EMIC waves; He+ ion heating; Ring current ions; stop band; Van Allen Probes |
|
In situ evidence of the modification of the parallel propagation of EMIC waves by heated He + ions With observations of the Van Allen Probe B, we report in situ evidence of the modification of the parallel propagating electromagnetic ion cyclotron (EMIC) waves by heated He+ ions. In the outer boundary of the plasmasphere, accompanied with the He+ ion heating, the frequency bands of H+ and He+ for EMIC waves merged into each other, leading to the disappearance of a usual stop band between the gyrofrequency of He+ ions (ΩHe+) and the H+ cutoff frequency (ωH+co) in the cold plasma. Moreover, the dispersion relation for EMIC waves theoretically calculated with the observed plasma parameters also demonstrates that EMIC waves can indeed parallel propagate across ΩHe+. Therefore, the paper provides an in situ evidence of the modification of the parallel propagation of EMIC waves by heated He+ ions Yuan, Zhigang; Yu, Xiongdong; Wang, Dedong; Huang, Shiyong; Li, Haimeng; Yu, Tao; Qiao, Zheng; Wygant, John; Funsten, Herbert; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2016 YEAR: 2016 DOI: 10.1002/2016JA022573 EMIC waves; He+ ion heating; Ring current ions; stop band; Van Allen Probes |
|
Using the Van Allen Probe in-situ measured magnetic field and electron data, we examine the solar wind dynamic pressure and interplanetary magnetic field (IMF) effects on global magnetic field and outer radiation belt relativistic electrons (>=1.8 MeV). The dynamic pressure enhancements (>2nPa) cause the dayside magnetic field increase and the nightside magnetic field reduction, whereas the large southward IMFs (Bz-IMF < -2nT) mainly lead to the decrease of the nightside magnetic field. In the dayside increased magnetic field region (MLT ~ 06:00 - 18:00, and L > 4), the pitch angles of relativistic electrons are mainly pancake distributions with a flux peak around 90o (corresponding anisotropic index A > 0.1), and the higher-energy electrons have stronger pancake distributions (the larger A), suggesting that the compression-induced betatron accelerations enhance the dayside pancake distributions. However in the nighttime decreased magnetic field region (MLT ~ 18:00 - 06:00, and L >= 5), the pitch angles of relativistic electrons become butterfly distributions with two flux peaks around 45o and 135o (A < 0). The spatial range of the nighttime butterfly distributions is almost independent of the relativistic electron energy, but it depends on the magnetic field day-night asymmetry and the interplanetary conditions. The dynamic pressure enhancements can make the nighttime butterfly distribution extend inward. The large southward IMFs can also lead to the azimuthal expansion of the nighttime butterfly distributions. These variations are consistent with the drift shell splitting and/or magnetopause shadowing effect. Yu, J.; Li, L.Y.; Cao, J.; Reeves, G.; Baker, D.; Spence, H.; Published by: Geophysical Research Letters Published on: 06/2016 YEAR: 2016 DOI: 10.1002/2016GL069029 butterfly distributions; Day-night asymmetrical variations of magnetic field; Day-night asymmetrical variations of relativistic electron pitch angle distributions; Pancake distributions; solar wind dynamic pressure; Southward interplanetary magnetic field; Van Allen Probes |
|
Interactions between interplanetary (IP) shocks and the Earth\textquoterights magnetosphere manifest many important space physics phenomena including low-energy ion flux enhancements and particle acceleration. In order to investigate the mechanisms driving shock-induced enhancement of low-energy ion flux, we have examined two IP shock events that occurred when the Van Allen Probes were located near the equator while ionospheric and ground observations were available around the spacecraft footprints. We have found that, associated with the shock arrival, electromagnetic fields intensified, and low-energy ion fluxes, including H+, He+, and O+, were enhanced dramatically in both the parallel and perpendicular directions. During the 2 October 2013 shock event, both parallel and perpendicular flux enhancements lasted more than 20 min with larger fluxes observed in the perpendicular direction. In contrast, for the 15 March 2013 shock event, the low-energy perpendicular ion fluxes increased only in the first 5 min during an impulse of electric field, while the parallel flux enhancement lasted more than 30 min. In addition, ionospheric outflows were observed after shock arrivals. From a simple particle motion calculation, we found that the rapid response of low-energy ions is due to drifts of plasmaspheric population by the enhanced electric field. However, the fast acceleration in the perpendicular direction cannot solely be explained by E \texttimes B drift but betatron acceleration also plays a role. Adiabatic acceleration may also explain the fast response of the enhanced parallel ion fluxes, while ion outflows may contribute to the enhanced parallel fluxes that last longer than the perpendicular fluxes. Yue, Chao; Li, Wen; Nishimura, Yukitoshi; Zong, Qiugang; Ma, Qianli; Bortnik, Jacob; Thorne, Richard; Reeves, Geoffrey; Spence, Harlan; Kletzing, Craig; Wygant, John; Nicolls, Michael; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2016 YEAR: 2016 DOI: 10.1002/2016JA022808 adiabatic accelerations; enhancement of low-energy ion flux; ionospheric ion outflows; response to IP shocks; Van Allen Probes |
|
Compressional ULF wave modulation of energetic particles in the inner magnetosphere We present Van Allen Probes observations of modulations in the flux of very energetic electrons up to a few MeV and protons between 1200 - 1400 UT on February 19th, 2014. During this event the spacecraft were in the dayside magnetosphere at L*≈5.5. The modulations extended across a wide range of particle energies, from 79.80 keV to 2.85 MeV for electrons and from 82.85 keV to 636.18 keV for protons. The fluxes of π/2 pitch angle particles were observed to attain maximum values simultaneously with the ULF compressional magnetic field component reaching a minimum. We use peak-to-valley ratios to quantify the strength of the modulation effect, finding that the modulation is larger at higher energies than at lower energies. It is shown that the compressional wave modulation of the particle distribution is due to the mirror effect, which can trap relativistic electrons efficiently for energies up to 2.85 MeV, and trap protons up to ≈600 keV. Larger peak-to-valley ratios at higher energies also attributed to the mirror effect. Finally, we suggest that protons with energies higher than 636.18 keV can not be trapped by the compressional ULF wave efficiently due to the finite Larmor radius effect. Liu, H.; Zong, Q.-G.; Zhou, X.-Z.; Fu, S; Rankin, R.; Wang, L.-H.; Yuan, C.; Wang, Y.; Baker, D.; Blake, J.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2016JA022706 Compressional ULF wave; energetic particles; Magnetosphere; Mirror effect; Modulation; relativistic electrons; Van Allen Probes |
|
Electron dropout echoes induced by interplanetary shock: Van Allen Probes observations On 23 November 2012, a sudden dropout of the relativistic electron flux was observed after an interplanetary shock arrival. The dropout peaks at \~1MeV and more than 80\% of the electrons disappeared from the drift shell. Van Allen twin Probes observed a sharp electron flux dropout with clear energy dispersion signals. The repeating flux dropout and recovery signatures, or \textquotedblleftdropout echoes\textquotedblright, constitute a new phenomenon referred to as a \textquotedblleftdrifting electron dropout\textquotedblright with a limited initial spatial range. The azimuthal range of the dropout is estimated to be on the duskside, from \~1300 to 0100 LT. We conclude that the shock-induced electron dropout is not caused by the magnetopause shadowing. The dropout and consequent echoes suggest that the radial migration of relativistic electrons is induced by the strong dusk-dawn asymmetric interplanetary shock compression on the magnetosphere Hao, Y.; Zong, Q.-G.; Zhou, X.-Z.; Fu, S; Rankin, R.; Yuan, C.-J.; T. Y. Lui, A.; Spence, H.; Blake, J.; Baker, D.; Reeves, G.; Published by: Geophysical Research Letters Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2016GL069140 Drift shell splitting; electron dropout echo; energetic particle; interplanetary shock; magnetopause shadowing; solar wind-magnetospheric coupling; Van Allen Probes |
| 2015 |
|
By examining the compression-induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP-A/B), we find that the relativistic electrons (>2MeV) outside the heart of outer radiation belt (L*>= 5) undergo multiple losses during a storm sudden commencement (SSC). The relativistic electron loss mainly occurs in the field-aligned direction (pitch angle α< 30\textdegree or >150\textdegree), and the flux decay of the field-aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30\textdegree-150\textdegree increase (decrease) with the decreasing (increasing) geocentric distance (|ΔL|< 0.25) of the RBSP-B (RBSP-A) location, and the electron fluxes in the quasi-perpendicular direction display energy-dispersive oscillations in the Pc5 period range (2 - 10min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high-L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850km) and magnetic field fluctuations in the Pc5 band. The intense EMIC waves and whistler-mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 hours. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high-L region with a negative electron phase space density gradient. Yu, J.; Li, L.Y.; Cao, J.; Yuan, Z.; Reeves, G.; Baker, D.; Blake, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021460 Electromagnetic ion cyclotron (EMIC) waves; outer radiation belt; Outward radial diffusion driven by ULF waves; Plasmaspheric Hiss; relativistic electron loss; Storm sudden commencement; Van Allen Probes |
|
By examining the compression-induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP-A/B), we find that the relativistic electrons (>2MeV) outside the heart of outer radiation belt (L*>= 5) undergo multiple losses during a storm sudden commencement (SSC). The relativistic electron loss mainly occurs in the field-aligned direction (pitch angle α< 30\textdegree or >150\textdegree), and the flux decay of the field-aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30\textdegree-150\textdegree increase (decrease) with the decreasing (increasing) geocentric distance (|ΔL|< 0.25) of the RBSP-B (RBSP-A) location, and the electron fluxes in the quasi-perpendicular direction display energy-dispersive oscillations in the Pc5 period range (2 - 10min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high-L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850km) and magnetic field fluctuations in the Pc5 band. The intense EMIC waves and whistler-mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 hours. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high-L region with a negative electron phase space density gradient. Yu, J.; Li, L.Y.; Cao, J.; Yuan, Z.; Reeves, G.; Baker, D.; Blake, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021460 Electromagnetic ion cyclotron (EMIC) waves; outer radiation belt; Outward radial diffusion driven by ULF waves; Plasmaspheric Hiss; relativistic electron loss; Storm sudden commencement; Van Allen Probes |
|
The Van-Allen probes, low-altitude NOAA satellite, MetOp satellite and riometer are used to analyze variations of precipitating energetic electron fluxes and cosmic radio noise absorption (CNA) driven by plasmaspheric hiss with respect to geomagnetic activities. The hiss-driven energetic electron precipitations (at L~4.7-5.3, MLT~8-9) are observed during geomagnetic quiet condition and substorms, respectively. We find that the CNA detected by riometers increased very little in the hiss-driven event during quiet condition on September 06, 2012. The hiss-driven enhancement of riometer was still little during the first substorm on September 30, 2012. However, the absorption detected by the riometer largely increased while the energies of the injected electrons became higher during the second substorm on September 30, 2012. The enhancement of CNA (ΔCNA) observed by the riometer and calculated with precipitating energetic electrons are in agreement during the second substorm, implying that the precipitating energetic electrons increase CNA to an obviously detectable level of the riometer during the second substorm on September 30, 2012. The conclusion is consistent with Rodger et al. (2012), which suggests that the higher level of ΔCNA prefer to occur in the substorms, because substorms may produce more intense energetic electron precipitation associated with electron injection. Furthermore, the combination of the observations and theory calculations also suggests that higher-energy electron (>55 keV) precipitation contribute more to the ΔCNA than the lower-energy electron precipitation. In this paper, the higher-energy electron precipitation is related to lower-frequency hiss. Li, Haimeng; Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Wang, Dedong; Wang, Zhenzhen; Qiao, Zheng; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021113 cosmic radio noise absorption; energetic electron precipitation; hiss; substorm; Van Allen Probes |
|
The Van-Allen probes, low-altitude NOAA satellite, MetOp satellite and riometer are used to analyze variations of precipitating energetic electron fluxes and cosmic radio noise absorption (CNA) driven by plasmaspheric hiss with respect to geomagnetic activities. The hiss-driven energetic electron precipitations (at L~4.7-5.3, MLT~8-9) are observed during geomagnetic quiet condition and substorms, respectively. We find that the CNA detected by riometers increased very little in the hiss-driven event during quiet condition on September 06, 2012. The hiss-driven enhancement of riometer was still little during the first substorm on September 30, 2012. However, the absorption detected by the riometer largely increased while the energies of the injected electrons became higher during the second substorm on September 30, 2012. The enhancement of CNA (ΔCNA) observed by the riometer and calculated with precipitating energetic electrons are in agreement during the second substorm, implying that the precipitating energetic electrons increase CNA to an obviously detectable level of the riometer during the second substorm on September 30, 2012. The conclusion is consistent with Rodger et al. (2012), which suggests that the higher level of ΔCNA prefer to occur in the substorms, because substorms may produce more intense energetic electron precipitation associated with electron injection. Furthermore, the combination of the observations and theory calculations also suggests that higher-energy electron (>55 keV) precipitation contribute more to the ΔCNA than the lower-energy electron precipitation. In this paper, the higher-energy electron precipitation is related to lower-frequency hiss. Li, Haimeng; Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Wang, Dedong; Wang, Zhenzhen; Qiao, Zheng; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021113 cosmic radio noise absorption; energetic electron precipitation; hiss; substorm; Van Allen Probes |
|
Simultaneous Pi2 observations by the Van Allen Probes inside and outside the plasmasphere Plasmaspheric virtual resonance (PVR) model has been proposed as one of source mechanisms for low-latitude Pi2 pulsations. Since PVR-associated Pi2 pulsations are not localized inside the plasmasphere, simultaneous multipoint observations inside and outside the plasmasphere require to test the PVR model. Until now, however, there are few studies using simultaneous multisatellite observations inside and outside the plasmasphere for understanding the radial structure of Pi2 pulsation. In this study, we focus on the Pi2 event observed at low-latitude Bohyun (BOH, L = 1.35) ground station in South Korea in the postmidnight sector (magnetic local time (MLT) = 3.0) for the interval from 1730 to 1900 UT on 12 March 2013. By using electron density derived from the frequency of the upper hybrid waves detected at Van Allen Probe-A (VAP-A) and Van Allen Probe-B (VAP-B), the plasmapause is identified. At the time of the Pi2 event, VAP-A was outside the plasmasphere near midnight (00:55 MLT and L = ~6), while VAP-B was inside the plasmasphere in the postmidnight sector (02:15 MLT and L = ~5). VAP-B observed oscillations in the compressional magnetic field component (Bz) and the dawn-to-dusk electric field component (Ey), having high coherence with the BOH Pi2 pulsation in the H component. The H - Bz and H - Ey cross phases at VAP-B inside the plasmasphere were near -180\textdegree and -90\textdegree, respectively.These phase relationships among Bz, Ey, and H are consistent with a radially standing oscillation of the fundamental mode reported in previous studies. At VAP-A outside the plasmasphere, Bz oscillations were highly correlated with BOH Pi2 pulsations with ~-180\textdegree phase delay, and the H-Ey cross phase is near -90\textdegree. From these two-satellite observations, we suggest that the fundamental PVR mode is directly detected by VAP-A and VAP-B. Ghamry, E.; Kim, K.-H.; Kwon, H.-J.; Lee, D.-H.; Park, J.-S.; Choi, J.; Hyun, K.; Kurth, W.; Kletzing, C.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021095 Pi2; plasmasphere; Plasmaspheric virtual resonance; Van Allen Probes |
|
Statistical characteristic of EMIC waves: Van Allen Probe observations Utilizing the data from the magnetometer instrument which is a part of the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument suite onboard the Van Allen Probe A from Sep. 2012 to Apr. 2014, when the apogee of the satellite has passed all the MLT sectors, we obtain the statistical distribution characteristic of EMIC waves in the inner magnetosphere over all local times from L=3 to L=6. Compared with the previous statistical results about EMIC waves, the occurrence rates of EMIC waves distribute relatively uniform in the MLT sectors in lower L-shells. On the other hand, in higher L-shells, there are indeed some peaks of the occurrence rate for the EMIC waves, especially in the noon, dusk and night sectors. EMIC waves appear at lower L-shells in the dawn sector than in other sectors. In the lower L-shells (L<4), the occurrence rates of EMIC waves are significant in the dawn sector. This phenomenon may result from the distribution characteristic of the plasmasphere. The location of the plasmapause is usually lower in the dawn sector than that in other sectors, and the plasmapause is considered to be the favored region for the generation of EMIC waves. In higher L-shells (L>4) the occurrence rates of EMIC waves are most significant in the dusk sector, implying the important role of the plasmapause or plasmaspheric plume in generating EMIC waves. We have also investigated the distribution characteristics of the hydrogen band and the helium band EMIC waves. Surprisingly, in the inner magnetosphere, the hydrogen band EMIC waves occur more frequently than the helium band EMIC waves. Both them have peaks of occurrence rate in noon, dusk and night sectors, and the hydrogen band EMIC waves have more obvious peaks than the helium band EMIC waves in the night sector, while the helium band EMIC waves are more concentrated than the hydrogen band EMIC waves in the dusk sector. Both them occur significantly in the noon sector, which implies the important role of the solar wind dynamic pressure. Wang, Dedong; Yuan, Zhigang; Yu, Xiongdong; Deng, Xiaohua; Zhou, Meng; Huang, Shiyong; Li, Haimeng; Wang, Zhenzhen; Qiao, Zheng; Kletzing, C.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021089 |
|
Statistical characteristic of EMIC waves: Van Allen Probe observations Utilizing the data from the magnetometer instrument which is a part of the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument suite onboard the Van Allen Probe A from Sep. 2012 to Apr. 2014, when the apogee of the satellite has passed all the MLT sectors, we obtain the statistical distribution characteristic of EMIC waves in the inner magnetosphere over all local times from L=3 to L=6. Compared with the previous statistical results about EMIC waves, the occurrence rates of EMIC waves distribute relatively uniform in the MLT sectors in lower L-shells. On the other hand, in higher L-shells, there are indeed some peaks of the occurrence rate for the EMIC waves, especially in the noon, dusk and night sectors. EMIC waves appear at lower L-shells in the dawn sector than in other sectors. In the lower L-shells (L<4), the occurrence rates of EMIC waves are significant in the dawn sector. This phenomenon may result from the distribution characteristic of the plasmasphere. The location of the plasmapause is usually lower in the dawn sector than that in other sectors, and the plasmapause is considered to be the favored region for the generation of EMIC waves. In higher L-shells (L>4) the occurrence rates of EMIC waves are most significant in the dusk sector, implying the important role of the plasmapause or plasmaspheric plume in generating EMIC waves. We have also investigated the distribution characteristics of the hydrogen band and the helium band EMIC waves. Surprisingly, in the inner magnetosphere, the hydrogen band EMIC waves occur more frequently than the helium band EMIC waves. Both them have peaks of occurrence rate in noon, dusk and night sectors, and the hydrogen band EMIC waves have more obvious peaks than the helium band EMIC waves in the night sector, while the helium band EMIC waves are more concentrated than the hydrogen band EMIC waves in the dusk sector. Both them occur significantly in the noon sector, which implies the important role of the solar wind dynamic pressure. Wang, Dedong; Yuan, Zhigang; Yu, Xiongdong; Deng, Xiaohua; Zhou, Meng; Huang, Shiyong; Li, Haimeng; Wang, Zhenzhen; Qiao, Zheng; Kletzing, C.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021089 |
|
Local acceleration via whistler wave and particle interaction plays a significant role in particle dynamics in the radiation belt. In this work we explore gyroresonant wave-particle interaction and quasi-linear diffusion in different magnetic field configurations related to the 17 March 2013 storm. We consider the Earth\textquoterights magnetic dipole field as a reference and compare the results against nondipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with the ring current-atmosphere interactions model with a self-consistent magnetic field (RAM-SCB), a code that models the Earth\textquoterights ring current and provides a realistic modeling of the Earth\textquoterights magnetic field. By applying quasi-linear theory, the bounce- and Magnetic Local Time (MLT)-averaged electron pitch angle, mixed-term, and energy diffusion coefficients are calculated for each magnetic field configuration. For radiation belt (\~1 MeV) and ring current (\~100 keV) electrons, it is shown that at some MLTs the bounce-averaged diffusion coefficients become rather insensitive to the details of the magnetic field configuration, while at other MLTs storm conditions can expand the range of equatorial pitch angles where gyroresonant diffusion occurs and significantly enhance the diffusion rates. When MLT average is performed at drift shell L=4.25 (a good approximation to drift average), the diffusion coefficients become quite independent of the magnetic field configuration for relativistic electrons, while the opposite is true for lower energy electrons. These results suggest that, at least for the 17 March 2013 storm and for L≲4.25, the commonly adopted dipole approximation of the Earth\textquoterights magnetic field can be safely used for radiation belt electrons, while a realistic modeling of the magnetic field configuration is necessary to describe adequately the diffusion rates of ring current electrons. Zhao, Lei; Yu, Yiqun; Delzanno, Gian; Jordanova, Vania; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020858 |
|
In situ observations of EMIC waves in O + band by the Van Allen Probe A Through polarization and spectra analysis of the magnetic field observed by the Van Allen Probe A, we present two typical cases of O+ band EMIC waves in the outer plasmasphere or plasma trough. Although such O+ band EMIC waves are rarely observed, 18 different events of O+ band EMIC waves (16 events in the outer plasmasphere and 2 events in the plasma trough) are found from September 2012 to August 2014 with observations of the Van Allen Probe A. We find that the preferred region for the occurrence of O+ band EMIC waves is in L = 2-5 and MLT = 03-13, 19-20, which is in accordance with the occurrence region of O+ ion torus. Therefore, our result suggests that the O+ ion torus in the outer plasmasphere during geomagnetic activities should play an important role in the generation of EMIC waves in O+ band. Yu, Xiongdong; Yuan, Zhigang; Wang, Dedong; Li, Haimeng; Huang, Shiyong; Wang, Zhenzhen; Zheng, Qiao; Zhou, Mingxia; Kletzing, C.; Wygant, J.; Published by: Geophysical Research Letters Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2015GL063250 |