Bibliography
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Found 1116 entries in the Bibliography.
Showing entries from 851 through 900
| 2014 |
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Characterization of the energy-dependent response of riometer absorption Ground based riometers provide an inexpensive means to continuously remote sense the precipitation of electrons in the dynamic auroral region of Earth\textquoterights ionosphere. The energy-dependent relationship between riometer absorption and precipitating electrons is thus of great importance for understanding the loss of electrons from the Earth\textquoterights magnetosphere. In this study, statistical and event-based analyses are applied to determine the energy of electrons to which riometers chiefly respond. Time-lagged correlation analysis of trapped to precipitating fluxes shows that daily averaged absorption best correlates with ~ 60 keV trapped electron flux at zero-time lag, although large variability is observed across different phases of the solar cycle. High-time resolution statistical cross-correlation analysis between signatures observed by riometer stations, and assuming electron motion due to gradient and curvature drift, results in inferred energies of 10-100 keV, with a clear maximum in occurrence for 40-60 keV electrons. One event is considered in detail utilizing riometer absorption signatures obtained from several stations. The mean inferred energies for the initial rise time and peak of the absorption after correction for electric field effects were ~70 keV, and ~60 keV, respectively. The analyses presented provide a means to characterize the energy of electrons to which riometers are responding in both a statistical sense, and during the evolution of individual events. Kellerman, A.; Shprits, Y; Makarevich, R.; Spanswick, E.; Donovan, E.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020027 cosmic noise absorption; electron energy; particle modeling; Radiation belts; riometer; electron precipitation |
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Characterization of the energy-dependent response of riometer absorption Ground based riometers provide an inexpensive means to continuously remote sense the precipitation of electrons in the dynamic auroral region of Earth\textquoterights ionosphere. The energy-dependent relationship between riometer absorption and precipitating electrons is thus of great importance for understanding the loss of electrons from the Earth\textquoterights magnetosphere. In this study, statistical and event-based analyses are applied to determine the energy of electrons to which riometers chiefly respond. Time-lagged correlation analysis of trapped to precipitating fluxes shows that daily averaged absorption best correlates with ~ 60 keV trapped electron flux at zero-time lag, although large variability is observed across different phases of the solar cycle. High-time resolution statistical cross-correlation analysis between signatures observed by riometer stations, and assuming electron motion due to gradient and curvature drift, results in inferred energies of 10-100 keV, with a clear maximum in occurrence for 40-60 keV electrons. One event is considered in detail utilizing riometer absorption signatures obtained from several stations. The mean inferred energies for the initial rise time and peak of the absorption after correction for electric field effects were ~70 keV, and ~60 keV, respectively. The analyses presented provide a means to characterize the energy of electrons to which riometers are responding in both a statistical sense, and during the evolution of individual events. Kellerman, A.; Shprits, Y; Makarevich, R.; Spanswick, E.; Donovan, E.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020027 cosmic noise absorption; electron energy; particle modeling; Radiation belts; riometer; electron precipitation |
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Electron lifetimes from narrowband wave-particle interactions within the plasmasphere This paper is devoted to the systematic study of electron lifetimes from narrowband wave-particle interactions within the plasmasphere. It relies on a new formulation of the bounce-averaged quasi-linear pitch angle diffusion coefficients parameterized by a single frequency, ω, and wave normal angle, θ. We first show that the diffusion coefficients scale with ω/Ωce, where Ωce is the equatorial electron gyrofrequency, and that maximal pitch angle diffusion occurs along the line α0 = π/2\textendashθ, where α0 is the equatorial pitch angle. Lifetimes are computed for L shell values in the range [1.5, 3.5] and energies, E, in the range [0.1, 6] MeV as a function of frequency and wave normal angle. The maximal pitch angle associated with a given lifetime is also given, revealing the frequencies that are able to scatter nearly equatorial pitch angle particles. The lifetimes are relatively independent of frequency and wave normal angle after taking into consideration the scaling law, with a weak dependence on wave normal angle up to 60\textendash70\textdegree, increasing to infinity as the wave normal angle approaches the resonance cone. We identify regions in the (L, E) plane in which a single wave type (hiss, VLF transmitters, or lightning-generated waves) is dominant relative to the others. We find that VLF waves dominate the lifetime for 0.2\textendash0.4 MeV at L ~ 2 and for 0.5\textendash0.8 MeV at L ~ 1.5, while hiss dominates the lifetime for 2\textendash3 MeV at L = 3\textendash3.5. The influence of lightning-generated waves is always mixed with the other two and cannot be easily differentiated. Limitations of the method for addressing effects due to restricted latitude or pitch angle domains are also discussed. Finally, for each (L, E) we search for the minimum lifetime and find that the optimal frequency that produces this lifetime increases as L diminishes. Restricting the search to very oblique waves, which could be emitted during the Demonstration and Science Experiments satellite mission, we find that the optimal frequency is always close to 0.16Ωce. Ripoll, J.-F.; Albert, J.; Cunningham, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020217 DSX; electron; narrowband; plasmasphere; wave-particle interactions |
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Excitation of nightside magnetosonic waves observed by Van Allen Probes During the recovery phase of the geomagnetic storm on 30-31 March 2013, Van Allen Probe A detected enhanced magnetosonic (MS) waves in a broad range of L =1.8-4.7 and MLT =17-22 h, with a frequency range ~10-100 Hz. In the meanwhile, distinct proton ring distributions with peaks at energies of ~10 keV, were also observed in L =3.2-4.6 and L =5.0-5.6. Using a subtracted bi-Maxwellian distribution to model the observed proton ring distribution, we perform three dimensional ray tracing to investigate the instability, propagation and spatial distribution of MS waves. Numerical results show that nightside MS waves are produced by proton ring distribution and grow rapidly from the source location L =5.6 to the location L =5.0, but remain nearly stable at locations L <5.0 Moreover, waves launched toward lower L-shells with different initial azimuthal angles propagate across different MLT regions with divergent paths at first, then gradually turn back toward higher L-shells and propagate across different MLT regions with convergent paths. The current results further reveal that MS waves are generated by a ring distribution of ~10 keV proton and proton ring in one region can contribute to the MS wave power in another region. Zhou, Qinghua; Xiao, Fuliang; Yang, Chang; Liu, Si; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020481 magnetosonic wave; RBSP results; Van Allen Probes; Wave-particle interaction |
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Feasibility study of astronaut standardized career dose limits in LEO and the outlook for BLEO Cosmic Study Group SG 3.19/1.10 was established in February 2013 under the aegis of the International Academy of Astronautics to consider and compare the dose limits adopted by various space agencies for astronauts in Low Earth Orbit. A preliminary definition of the limits that might later be adopted by crews exploring Beyond Low Earth Orbit was, in addition, to be made. The present paper presents preliminary results of the study reported at a Symposium held in Turin by the Academy in July 2013. First, an account is provided of exposure limits assigned by various partner space agencies to those of their astronauts that work aboard the International Space Station. Then, gaps in the scientific and technical information required to safely implement human missions beyond the shielding provided by the geomagnetic field (to the Moon, Mars and beyond) are identified. Among many recommendations for actions to mitigate the health risks potentially posed to personnel Beyond Low Earth Orbit is the development of a preliminary concept for a Human Space Awareness System to: provide for crewed missions the means of prompt onboard detection of the ambient arrival of hazardous particles; develop a strategy for the implementation of onboard responses to hazardous radiation levels; support modeling/model validation that would enable reliable predictions to be made of the arrival of hazardous radiation at a distant spacecraft; provide for the timely transmission of particle alerts to a distant crewed vehicle at an emergency frequency using suitably located support spacecraft. Implementation of the various recommendations of the study can be realized based on a two pronged strategy whereby Space Agencies/Space Companies/Private Entrepreneurial Organizations etc. address the mastering of required key technologies (e.g. fast transportation; customized spacecraft design) while the International Academy of Astronautics, in a role of handling global international co-operation, organizes complementary studies aimed at harnessing the strengths and facilities of emerging nations in investigating/solving related problems (e.g. advanced space radiation modeling/model validation; predicting the arrivals of Solar Energetic Particles and shocks at a distant spacecraft). Ongoing progress in pursuing these complementary parallel programs could be jointly reviewed bi-annually by the Space Agencies and the International Academy of Astronautics so as to maintain momentum and direction in globally progressing towards feasible human exploration of interplanetary space. Published by: Acta Astronautica Published on: 11/2014 YEAR: 2014 DOI: 10.1016/j.actaastro.2014.07.011 Dose limits; Galactic Cosmic Radiation; Solar Energetic Particles |
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First observation of rising-tone magnetosonic waves Magnetosonic (MS) waves are linearly polarized emissions confined near the magnetic equator with wave normal angle near 90\textdegree and frequency below the lower hybrid frequency. Such waves, also termed equatorial noise, were traditionally known to be \textquotedbllefttemporally continuous\textquotedblright in their time-frequency spectrogram. Here we show for the first time that MS waves actually have discrete wave elements with rising-tone features in their spectrogram. The frequency sweep rate of MS waves, ~1 Hz/s, is between that of chorus and electromagnetic ion cyclotron (EMIC) waves. For the two events we analyzed, MS waves occur outside the plasmapause and cannot penetrate into the plasmasphere; their power is smaller than that of chorus. We suggest that the rising-tone feature of MS waves is a consequence of nonlinear wave-particle interaction, as is the case with chorus and EMIC waves. Fu, H.; Cao, J.; Zhima, Z.; Khotyaintsev, Y.; Angelopoulos, V.; ik, O.; Omura, Y.; Taubenschuss, U.; Chen, L.; Huang, S; Published by: Geophysical Research Letters Published on: 11/2014 YEAR: 2014 DOI: 10.1002/grl.v41.2110.1002/2014GL061867 discrete; frequency sweep rate; magnetosonic wave; nonlinear wave-particle interaction; Plasmapause; rising tone |
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First observation of rising-tone magnetosonic waves Magnetosonic (MS) waves are linearly polarized emissions confined near the magnetic equator with wave normal angle near 90\textdegree and frequency below the lower hybrid frequency. Such waves, also termed equatorial noise, were traditionally known to be \textquotedbllefttemporally continuous\textquotedblright in their time-frequency spectrogram. Here we show for the first time that MS waves actually have discrete wave elements with rising-tone features in their spectrogram. The frequency sweep rate of MS waves, ~1 Hz/s, is between that of chorus and electromagnetic ion cyclotron (EMIC) waves. For the two events we analyzed, MS waves occur outside the plasmapause and cannot penetrate into the plasmasphere; their power is smaller than that of chorus. We suggest that the rising-tone feature of MS waves is a consequence of nonlinear wave-particle interaction, as is the case with chorus and EMIC waves. Fu, H.; Cao, J.; Zhima, Z.; Khotyaintsev, Y.; Angelopoulos, V.; ik, O.; Omura, Y.; Taubenschuss, U.; Chen, L.; Huang, S; Published by: Geophysical Research Letters Published on: 11/2014 YEAR: 2014 DOI: 10.1002/grl.v41.2110.1002/2014GL061867 discrete; frequency sweep rate; magnetosonic wave; nonlinear wave-particle interaction; Plasmapause; rising tone |
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First observation of rising-tone magnetosonic waves Magnetosonic (MS) waves are linearly polarized emissions confined near the magnetic equator with wave normal angle near 90\textdegree and frequency below the lower hybrid frequency. Such waves, also termed equatorial noise, were traditionally known to be \textquotedbllefttemporally continuous\textquotedblright in their time-frequency spectrogram. Here we show for the first time that MS waves actually have discrete wave elements with rising-tone features in their spectrogram. The frequency sweep rate of MS waves, ~1 Hz/s, is between that of chorus and electromagnetic ion cyclotron (EMIC) waves. For the two events we analyzed, MS waves occur outside the plasmapause and cannot penetrate into the plasmasphere; their power is smaller than that of chorus. We suggest that the rising-tone feature of MS waves is a consequence of nonlinear wave-particle interaction, as is the case with chorus and EMIC waves. Fu, H.; Cao, J.; Zhima, Z.; Khotyaintsev, Y.; Angelopoulos, V.; ik, O.; Omura, Y.; Taubenschuss, U.; Chen, L.; Huang, S; Published by: Geophysical Research Letters Published on: 11/2014 YEAR: 2014 DOI: 10.1002/grl.v41.2110.1002/2014GL061867 discrete; frequency sweep rate; magnetosonic wave; nonlinear wave-particle interaction; Plasmapause; rising tone |
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An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts Early observations1, 2 indicated that the Earth\textquoterights Van Allen radiation belts could be separated into an inner zone dominated by high-energy protons and an outer zone dominated by high-energy electrons. Subsequent studies3, 4 showed that electrons of moderate energy (less than about one megaelectronvolt) often populate both zones, with a deep \textquoteleftslot\textquoteright region largely devoid of particles between them. There is a region of dense cold plasma around the Earth known as the plasmasphere, the outer boundary of which is called the plasmapause. The two-belt radiation structure was explained as arising from strong electron interactions with plasmaspheric hiss just inside the plasmapause boundary5, with the inner edge of the outer radiation zone corresponding to the minimum plasmapause location6. Recent observations have revealed unexpected radiation belt morphology7, 8, especially at ultrarelativistic kinetic energies9, 10 (more than five megaelectronvolts). Here we analyse an extended data set that reveals an exceedingly sharp inner boundary for the ultrarelativistic electrons. Additional, concurrently measured data11 reveal that this barrier to inward electron radial transport does not arise because of a physical boundary within the Earth\textquoterights intrinsic magnetic field, and that inward radial diffusion is unlikely to be inhibited by scattering by electromagnetic transmitter wave fields. Rather, we suggest that exceptionally slow natural inward radial diffusion combined with weak, but persistent, wave\textendashparticle pitch angle scattering deep inside the Earth\textquoterights plasmasphere can combine to create an almost impenetrable barrier through which the most energetic Van Allen belt electrons cannot migrate. Baker, D.; Jaynes, A.; Hoxie, V.; Thorne, R.; Foster, J.; Li, X.; Fennell, J.; Wygant, J.; Kanekal, S.; Erickson, P.; Kurth, W.; Li, W.; Ma, Q.; Schiller, Q.; Blum, L.; Malaspina, D.; Gerrard, A.; Lanzerotti, L.; Published by: Nature Published on: 11/2014 YEAR: 2014 DOI: 10.1038/nature13956 Magnetospheric physics; ultrarelativistic electrons; Van Allen Belts; Van Allen Probes |
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An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts Early observations1, 2 indicated that the Earth\textquoterights Van Allen radiation belts could be separated into an inner zone dominated by high-energy protons and an outer zone dominated by high-energy electrons. Subsequent studies3, 4 showed that electrons of moderate energy (less than about one megaelectronvolt) often populate both zones, with a deep \textquoteleftslot\textquoteright region largely devoid of particles between them. There is a region of dense cold plasma around the Earth known as the plasmasphere, the outer boundary of which is called the plasmapause. The two-belt radiation structure was explained as arising from strong electron interactions with plasmaspheric hiss just inside the plasmapause boundary5, with the inner edge of the outer radiation zone corresponding to the minimum plasmapause location6. Recent observations have revealed unexpected radiation belt morphology7, 8, especially at ultrarelativistic kinetic energies9, 10 (more than five megaelectronvolts). Here we analyse an extended data set that reveals an exceedingly sharp inner boundary for the ultrarelativistic electrons. Additional, concurrently measured data11 reveal that this barrier to inward electron radial transport does not arise because of a physical boundary within the Earth\textquoterights intrinsic magnetic field, and that inward radial diffusion is unlikely to be inhibited by scattering by electromagnetic transmitter wave fields. Rather, we suggest that exceptionally slow natural inward radial diffusion combined with weak, but persistent, wave\textendashparticle pitch angle scattering deep inside the Earth\textquoterights plasmasphere can combine to create an almost impenetrable barrier through which the most energetic Van Allen belt electrons cannot migrate. Baker, D.; Jaynes, A.; Hoxie, V.; Thorne, R.; Foster, J.; Li, X.; Fennell, J.; Wygant, J.; Kanekal, S.; Erickson, P.; Kurth, W.; Li, W.; Ma, Q.; Schiller, Q.; Blum, L.; Malaspina, D.; Gerrard, A.; Lanzerotti, L.; Published by: Nature Published on: 11/2014 YEAR: 2014 DOI: 10.1038/nature13956 Magnetospheric physics; ultrarelativistic electrons; Van Allen Belts; Van Allen Probes |
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H-ion (~45-keV to ~600-keV), He-ion (~65-keV to ~520-keV), and O-ion (~140-keV to ~1130-keV) integral flux measurements, from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft B, are reported. These abundance data form a cohesive picture of ring current ions during the first nine months of measurements. Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio. Of unique interest to ring current dynamics are the spatial-temporal decay characteristics of the two injected populations. We observe that He-ions decay more quickly at lower L-shells, on the orderof ~0.8-day at L-shells of 3\textendash4, and decay more slowly with higher L-shell, on the order of ~1.7-days at L-shells of 5\textendash6. Conversely, O-ions decay very rapidly (~1.5-hours) across all L-shells. The He-ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange. The O-ion decay time is much faster than predicted and is attributed to the inclusion of higher energy (>500-keV) O-ions in our decay rate estimation. We note that these measurements demonstrate a compelling need for calculation of high energy O-ion loss rates, which have not been adequately studied in the literature to date. Gerrard, Andrew; Lanzerotti, Louis; Gkioulidou, Matina; Mitchell, Donald; Manweiler, Jerry; Bortnik, Jacob; Keika, Kunihiro; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020374 inner magnetosphere; ion decay rates; Spacecraft measurements; Van Allen Probes |
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On long decays of electrons in the vicinity of the slot region observed by HEO3 Long decay periods of electron counts, which follow abrupt rises and last from weeks to months, have been observed by the HEO3 spacecraft in the vicinity of the slot region between the years 1998 and 2007. During the most stable decay periods as selected, e-folding timescales are extracted and statistically analyzed from observations as a function of L-shell and electron energy. A challenge is to reproduce the observed timescales from simulations of pitch angle diffusion by three acting waves\textendashthe plasmaspheric hiss, lightning-generated whistlers, and VLF transmitter waves. We perform full numerical simulations to accurately compute electron lifetimes. We choose to use the method and wave parameters proposed by Abel \& Thorne [1998] with the goal to assess whether they can reproduce lifetimes extracted from HEO observations. We show how hiss dominantly affect high energy electrons (E > 2 MeV) for L in [2, 3.5] and VLF transmitter waves control residency times of low energy electrons (<0.4 MeV) around L = 2. These interactions induce characteristic shapes of the lifetime profiles that will be discussed. We show how the wave amplitudes can be adjusted for the particular energy particles that are dominantly affected by one wave type only. Using these amplitudes, mean HEO lifetimes are reproduced within a factor 2 to 5. VLF occurrence rates and hiss amplitude turn out significantly higher than those proposed by Abel \& Thorne [1998]. The wide energy response of the sensors complicates the analysis because it blurs the electron lifetime dependence on energy, increases the overall lifetimes and reduces the differences between the different channel lifetimes. In particular, our simulations suggest the flux measured by an integrated energy sensor aboard HEO has a variable slope, i.e. a variable lifetime, during 10-20 days in our data, due to the faster decay of the low residency time particles while slower decaying particles control the steady decay. It can explain some of the multi-slopes decays observed by HEO. HEO electron long decay timescales are also compared to the timescales previously observed from SAMPEX and CRRES with differences attributed to factors such as instrument characteristic and different satellite orbits. Ripoll, J.-F.; Chen, Y.; Fennell, J.; Friedel, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020449 |
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Following the conclusion of the 2014 Space Weather Week in Boulder, Colorado, the NOAA National Geophysical Data Center and Space Weather Prediction Center cohosted a 1 day workshop on the intercalibration of solar energetic particle (SEP) measurements. The overall purpose of this workshop was to discuss the intercalibration of SEP measurements from different instruments and different spacecraft, to foster new cooperative intercalibration efforts, and to identify a path forward for establishing a set of intercalibration guidelines. The detailed objectives of this workshop were described by Rodriguez and Onsager [2014]. Ten talks were given at the workshop (available at ftp://ftp.ngdc.noaa.gov/STP/publications/spe_intercal/), interspersed with extensive discussions. One outcome of these discussions is a recommendation that a set of guidelines be drafted for the on-orbit cross comparison of solar energetic particle measurements, similar to the first optical calibration guidelines developed for the Global Space-based Inter-Calibration System (GSICS) of the World Meteorological Organization (WMO) and the Coordination Group for Meteorological Satellites [Datla et al., 2009]. Rodriguez, Juan; Onsager, Terrance; Heynderickx, Daniel; Jiggens, Piers; Published by: Space Weather Published on: 11/2014 YEAR: 2014 DOI: 10.1002/swe.v12.1110.1002/2014SW001134 cross calibration; interoperability; Solar Energetic Particles |
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Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr < Ωe, where Ωe is the electron cyclotron frequency, and a characteristic spectral gap at ωr ≃ Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell (PIC) simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from HOPE instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper-band chorus, and that the hot component drives the electromagnetic lower-band chorus; the gap at \~ Ωe/2 is a natural consequence of the growth of two whistler modes with different properties. Fu, Xiangrong; Cowee, Misa; Friedel, Reinhard; Funsten, Herbert; Gary, Peter; Hospodarsky, George; Kletzing, Craig; Kurth, William; Larsen, Brian; Liu, Kaijun; MacDonald, Elizabeth; Min, Kyungguk; Reeves, Geoffrey; Skoug, Ruth; Winske, Dan; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014JA020364 |
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Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr < Ωe, where Ωe is the electron cyclotron frequency, and a characteristic spectral gap at ωr ≃ Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell (PIC) simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from HOPE instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper-band chorus, and that the hot component drives the electromagnetic lower-band chorus; the gap at \~ Ωe/2 is a natural consequence of the growth of two whistler modes with different properties. Fu, Xiangrong; Cowee, Misa; Friedel, Reinhard; Funsten, Herbert; Gary, Peter; Hospodarsky, George; Kletzing, Craig; Kurth, William; Larsen, Brian; Liu, Kaijun; MacDonald, Elizabeth; Min, Kyungguk; Reeves, Geoffrey; Skoug, Ruth; Winske, Dan; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014JA020364 |
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Magnetic search coils (MSCs) are sensitive to both magnetic and electric fields, but detecting electric fields is unnecessary for magnetic observations of plasma waves. However, it is important to evaluate both sensitivities for different geometries and electrostatic shields to avoid electric field pickup. An equivalent circuit model for the electric field sensitivity of an MSC in a collisionless isotropic cold plasma is developed here using electrical coupling through a sheath capacitance. That sensitivity is defined by a relationship between the MSC impedance and the sheath capacitance. To confirm the validity of the circuit model, the sensitivity to an electric field is measured by imposing an external electric field using charged parallel metallic plates in laboratory experiments. The coupling capacitance between the MSC and the charged plates is equivalent to the sheath capacitance in a space plasma. The measured results show good agreement with an approximate expression deduced from the equivalent circuit model. Ozaki, Mitsunori; Yagitani, Satoshi; Takahashi, Ken; Imachi, Tomohiko; Koji, Hiroki; Higashi, Ryoichi; Published by: IEEE Sensors Journal Published on: 10/2014 YEAR: 2014 DOI: 10.1109/JSEN.2014.2365495 electric field sensitivity; Magnetic search coils; sheath impedance; space plasmas |
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The Evolving Space Weather System - Van Allen Probes Contribution The overarching goal and purpose of the study of space weather is clear - to understand and address the issues caused by solar disturbances on humans and technological systems. Space weather has evolved in the past few decades from a collection of concerned agencies and researchers to a critical function of the National Weather Service of NOAA. The general effects have also evolved from the well-known telegraph disruptions of the mid-1800\textquoterights to modern day disturbances of the electric power grid, communications and navigation, human spaceflight and spacecraft systems. The last two items in this list, and specifically the effects of penetrating radiation, were the impetus for the space weather broadcast implemented on NASA\textquoterights Van Allen Probes\textquoteright twin pair of satellites, launched in August of 2012 and orbiting directly through Earth\textquoterights severe radiation belts. The Van Allen Probes mission, formerly the Radiation Belt Storm Probes (RBSP, http://vanallenprobes.jhuapl.edu), were renamed soon after launch to honor the discoverer of Earth\textquoterights radiation belts at the beginning of the space age, the late James Van Allen (the spacecraft themselves are still referred to as RBSP-A and RBSP-B). The Van Allen Probes (Mauk et al., 2012 and other team contributions in the same special issue of Space Science Reviews, 2012) are one part of NASA\textquoterights Living With a Star (LWS, http://lws.gsfc.nasa.gov) program formulated to advance the scientific understanding of the connection between solar disturbances, the resulting heliospheric conditions and their effects on the geospace and Earth environment. Zanetti, L.; Mauk, B.; Fox, N.J.; Barnes, R.J.; Weiss, M.; Sotirelis, T.S.; Raouafi, N.-E.; Kessel, R.; Becker, H.; Published by: Space Weather Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014SW001108 |
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We present in situ observations of a shock-induced substorm-like event on 13 April 2013 observed by the newly launched Van Allen twin probes. Substorm-like electron injections with energy of 30\textendash500 keV were observed in the region from L\~5.2 to 5.5 immediately after the shock arrival (followed by energetic electron drift echoes). Meanwhile, the electron flux was clearly and strongly varying on the ULF wave time scale. It is found that both toroidal and poloidal mode ULF waves with a period of 150 s emerged following the magnetotail magnetic field reconfiguration after the interplanetary (IP) shock passage. The poloidal mode is more intense than the toroidal mode. The 90\textdegree phase shift between the poloidal mode Br and Ea suggests the standing poloidal waves in the Northern Hemisphere. Furthermore, the energetic electron flux modulations indicate that the azimuthal wave number is \~14. Direct evidence of drift resonance between the injected electrons and the excited poloidal ULF wave has been obtained. The resonant energy is estimated to be between 150 keV and 230 keV. Two possible scenaria on ULF wave triggering are discussed: vortex-like flow structure-driven field line resonance and ULF wave growth through drift resonance. It is found that the IP shock may trigger intense ULF wave and energetic electron behavior at L\~3 to 6 on the nightside, while the time profile of the wave is different from dayside cases. Hao, Y.; Zong, Q.-G.; Wang, Y.; Zhou, X.-Z.; Zhang, Hui; Fu, S; Pu, Z; Spence, H.; Blake, J.; Bonnell, J.; Wygant, J.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014JA020023 energetic particles; interplanetary shock; magnetotail ULF wave; poloidal and toroidal mode; Van Allen Probes; wave-particle interactions |
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Statistical analysis of ground-based chorus observations during geomagnetic storms Chorus observations from two ground-based, Antarctic receiving stations are analyzed for a set of geomagnetic storms from 2000 to 2010. Superposed epoch analysis is performed together with statistical hypothesis testing to determine whether the observed quantities (geomagnetic indices, outer belt energetic electron fluxes, and chorus properties) are statistically significantly different as functions of storm phase, storm size, and storm type. Waves generated in the outer dayside magnetosphere and observed on the ground at South Pole Station are suppressed during main phase and are statistically unchanged from random intervals during recovery phase. Waves generated in the inner magnetosphere and observed on the ground at Palmer Station are significantly enhanced during storm main phase and for about 3 days into recovery. During main phase, there are larger enhancements in chorus occurrence, amplitude, and frequency extent as observed at Palmer during larger storms. During recovery phase, there are larger enhancements in chorus occurrence, amplitude, and frequency extent as observed at Palmer during larger storms and during storms where the average rate of electron flux increase, averaged across the outer belt, is higher. Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.1010.1002/2014JA019975 |
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THEMIS measurements of quasi-static electric fields in the inner magnetosphere We use four years of THEMIS double-probe measurements to offer, for the first time, a complete picture of the dawn-dusk electric field covering all local times and radial distances in the inner magnetosphere based on in situ equatorial observations. This study is motivated by the results from the CRRES mission, which revealed a local maximum in the electric field developing near Earth during storm times, rather than the expected enhancement at higher L shells that is shielded near Earth as suggested by the Volland-Stern model. The CRRES observations were limited to the dusk side, while THEMIS provides complete local time coverage. We show strong agreement with the CRRES results on the dusk side, with a local maximum near L =4 for moderate levels of geomagnetic activity and evidence of strong electric fields inside L =3 during the most active times. The extensive dataset from THEMIS also confirms the day/night asymmetry on the dusk side, where the enhancement is closest to Earth in the dusk-midnight sector, and is farther away closer to noon. A similar, but smaller in magnitude, local maximum is observed on the dawn side near L =4. The noon sector shows the smallest average electric fields, and for more active times, the enhancement develops near L =7 rather than L =4. We also investigate the impact of the uncertain boom-shorting factor on the results, and show that while the absolute magnitude of the electric field may be underestimated, the trends with geomagnetic activity remain intact. Califf, S.; Li, X.; Blum, L.; Jaynes, A.; Schiller, Q.; Zhao, H.; Malaspina, D.; Hartinger, M.; Wolf, R.; Rowland, D.; Wygant, J.; Bonnell, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014JA020360 convection; double probe; electric field; inner magnetosphere |
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THEMIS measurements of quasi-static electric fields in the inner magnetosphere We use four years of THEMIS double-probe measurements to offer, for the first time, a complete picture of the dawn-dusk electric field covering all local times and radial distances in the inner magnetosphere based on in situ equatorial observations. This study is motivated by the results from the CRRES mission, which revealed a local maximum in the electric field developing near Earth during storm times, rather than the expected enhancement at higher L shells that is shielded near Earth as suggested by the Volland-Stern model. The CRRES observations were limited to the dusk side, while THEMIS provides complete local time coverage. We show strong agreement with the CRRES results on the dusk side, with a local maximum near L =4 for moderate levels of geomagnetic activity and evidence of strong electric fields inside L =3 during the most active times. The extensive dataset from THEMIS also confirms the day/night asymmetry on the dusk side, where the enhancement is closest to Earth in the dusk-midnight sector, and is farther away closer to noon. A similar, but smaller in magnitude, local maximum is observed on the dawn side near L =4. The noon sector shows the smallest average electric fields, and for more active times, the enhancement develops near L =7 rather than L =4. We also investigate the impact of the uncertain boom-shorting factor on the results, and show that while the absolute magnitude of the electric field may be underestimated, the trends with geomagnetic activity remain intact. Califf, S.; Li, X.; Blum, L.; Jaynes, A.; Schiller, Q.; Zhao, H.; Malaspina, D.; Hartinger, M.; Wolf, R.; Rowland, D.; Wygant, J.; Bonnell, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2014 YEAR: 2014 DOI: 10.1002/2014JA020360 convection; double probe; electric field; inner magnetosphere |
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The Comprehensive Inner Magnetosphere-Ionosphere Model Simulation studies of the Earth\textquoterights radiation belts and ring current are very useful in understanding the acceleration, transport, and loss of energetic particles. Recently, the Comprehensive Ring Current Model (CRCM) and the Radiation Belt Environment (RBE) model were merged to form a Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. CIMI solves for many essential quantities in the inner magnetosphere, including ion and electron distributions in the ring current and radiation belts, plasmaspheric density, Region 2 currents, convection potential, and precipitation in the ionosphere. It incorporates whistler mode chorus and hiss wave diffusion of energetic electrons in energy, pitch angle, and cross terms. CIMI thus represents a comprehensive model that considers the effects of the ring current and plasmasphere on the radiation belts. We have performed a CIMI simulation for the storm on 5\textendash9 April 2010 and then compared our results with data from the Two Wide-angle Imaging Neutral-atom Spectrometers and Akebono satellites. We identify the dominant energization and loss processes for the ring current and radiation belts. We find that the interactions with the whistler mode chorus waves are the main cause of the flux increase of MeV electrons during the recovery phase of this particular storm. When a self-consistent electric field from the CRCM is used, the enhancement of MeV electrons is higher than when an empirical convection model is applied. We also demonstrate how CIMI can be a powerful tool for analyzing and interpreting data from the new Van Allen Probes mission. Fok, M.-C.; Buzulukova, N; Chen, S.-H.; Glocer, A.; Nagai, T.; Valek, P.; Perez, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.910.1002/2014JA020239 inner magnetosphere; magnetosphere-ionosphere coupling; ring current; Radiation belts; Van Allen Probes |
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The Comprehensive Inner Magnetosphere-Ionosphere Model Simulation studies of the Earth\textquoterights radiation belts and ring current are very useful in understanding the acceleration, transport, and loss of energetic particles. Recently, the Comprehensive Ring Current Model (CRCM) and the Radiation Belt Environment (RBE) model were merged to form a Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. CIMI solves for many essential quantities in the inner magnetosphere, including ion and electron distributions in the ring current and radiation belts, plasmaspheric density, Region 2 currents, convection potential, and precipitation in the ionosphere. It incorporates whistler mode chorus and hiss wave diffusion of energetic electrons in energy, pitch angle, and cross terms. CIMI thus represents a comprehensive model that considers the effects of the ring current and plasmasphere on the radiation belts. We have performed a CIMI simulation for the storm on 5\textendash9 April 2010 and then compared our results with data from the Two Wide-angle Imaging Neutral-atom Spectrometers and Akebono satellites. We identify the dominant energization and loss processes for the ring current and radiation belts. We find that the interactions with the whistler mode chorus waves are the main cause of the flux increase of MeV electrons during the recovery phase of this particular storm. When a self-consistent electric field from the CRCM is used, the enhancement of MeV electrons is higher than when an empirical convection model is applied. We also demonstrate how CIMI can be a powerful tool for analyzing and interpreting data from the new Van Allen Probes mission. Fok, M.-C.; Buzulukova, N; Chen, S.-H.; Glocer, A.; Nagai, T.; Valek, P.; Perez, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.910.1002/2014JA020239 inner magnetosphere; magnetosphere-ionosphere coupling; ring current; Radiation belts; Van Allen Probes |
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Ground-based ELF/VLF chorus observations at subauroral latitudes-VLF-CHAIN Campaign We report observations of very low frequency (VLF) and extremely low frequency (ELF) chorus waves taken during the ELF/VLF Campaign observation with High-resolution Aurora Imaging Network (VLF-CHAIN) of 17\textendash25 February 2012 at subauroral latitudes at Athabasca (L=4.3), Canada. ELF/VLF waves were measured continuously with a sampling rate of 100 kHz to monitor daily variations in ELF/VLF emissions and derive their detailed structures. We found quasiperiodic (QP) emissions whose repetition period changes rapidly within a period of 1 h without corresponding magnetic pulsations. QP emissions showed positive correlation between amplitude and frequency sweep rate, similarly to rising-tone elements. We found an event of nearly simultaneous enhancements of QP emissions and Pc1/electromagnetic ion cyclotron wave intensities, suggesting that the temperature anisotropy of electrons and ions developed simultaneously at the equatorial plane of the magnetosphere. We also found QP emissions whose intensity suddenly increased in association with storm sudden commencement without changing their frequency. Falling-tone ELF/VLF emissions were observed with their rate of frequency change varying from 0.7 to 0.05 kHz/s over 10 min. Bursty-patch emissions in the lower and upper frequency bands are often observed during magnetically disturbed periods. Clear systematic correlation between these various ELF/VLF emissions and cosmic noise absorption was not obtained throughout the campaign period. These observations indicate several previously unknown features of ELF/VLF emissions in subauroral latitudes and demonstrate the importance of continuous measurements for monitoring temporal variations in these emissions. Shiokawa, Kazuo; Yokoyama, Yu; Ieda, Akimasa; Miyoshi, Yoshizumi; Nomura, Reiko; Lee, Sungeun; Sunagawa, Naoki; Miyashita, Yukinaga; Ozaki, Mitsunori; Ishizaka, Kazumasa; Yagitani, Satoshi; Kataoka, Ryuho; Tsuchiya, Fuminori; Schofield, Ian; Connors, Martin; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.910.1002/2014JA020161 Chorus; ELF/VLF; Radiation belts; subauroral latitudes; wave-particle interactions |
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Ground-based ELF/VLF chorus observations at subauroral latitudes-VLF-CHAIN Campaign We report observations of very low frequency (VLF) and extremely low frequency (ELF) chorus waves taken during the ELF/VLF Campaign observation with High-resolution Aurora Imaging Network (VLF-CHAIN) of 17\textendash25 February 2012 at subauroral latitudes at Athabasca (L=4.3), Canada. ELF/VLF waves were measured continuously with a sampling rate of 100 kHz to monitor daily variations in ELF/VLF emissions and derive their detailed structures. We found quasiperiodic (QP) emissions whose repetition period changes rapidly within a period of 1 h without corresponding magnetic pulsations. QP emissions showed positive correlation between amplitude and frequency sweep rate, similarly to rising-tone elements. We found an event of nearly simultaneous enhancements of QP emissions and Pc1/electromagnetic ion cyclotron wave intensities, suggesting that the temperature anisotropy of electrons and ions developed simultaneously at the equatorial plane of the magnetosphere. We also found QP emissions whose intensity suddenly increased in association with storm sudden commencement without changing their frequency. Falling-tone ELF/VLF emissions were observed with their rate of frequency change varying from 0.7 to 0.05 kHz/s over 10 min. Bursty-patch emissions in the lower and upper frequency bands are often observed during magnetically disturbed periods. Clear systematic correlation between these various ELF/VLF emissions and cosmic noise absorption was not obtained throughout the campaign period. These observations indicate several previously unknown features of ELF/VLF emissions in subauroral latitudes and demonstrate the importance of continuous measurements for monitoring temporal variations in these emissions. Shiokawa, Kazuo; Yokoyama, Yu; Ieda, Akimasa; Miyoshi, Yoshizumi; Nomura, Reiko; Lee, Sungeun; Sunagawa, Naoki; Miyashita, Yukinaga; Ozaki, Mitsunori; Ishizaka, Kazumasa; Yagitani, Satoshi; Kataoka, Ryuho; Tsuchiya, Fuminori; Schofield, Ian; Connors, Martin; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.910.1002/2014JA020161 Chorus; ELF/VLF; Radiation belts; subauroral latitudes; wave-particle interactions |
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Ground-based ELF/VLF chorus observations at subauroral latitudes-VLF-CHAIN Campaign We report observations of very low frequency (VLF) and extremely low frequency (ELF) chorus waves taken during the ELF/VLF Campaign observation with High-resolution Aurora Imaging Network (VLF-CHAIN) of 17\textendash25 February 2012 at subauroral latitudes at Athabasca (L=4.3), Canada. ELF/VLF waves were measured continuously with a sampling rate of 100 kHz to monitor daily variations in ELF/VLF emissions and derive their detailed structures. We found quasiperiodic (QP) emissions whose repetition period changes rapidly within a period of 1 h without corresponding magnetic pulsations. QP emissions showed positive correlation between amplitude and frequency sweep rate, similarly to rising-tone elements. We found an event of nearly simultaneous enhancements of QP emissions and Pc1/electromagnetic ion cyclotron wave intensities, suggesting that the temperature anisotropy of electrons and ions developed simultaneously at the equatorial plane of the magnetosphere. We also found QP emissions whose intensity suddenly increased in association with storm sudden commencement without changing their frequency. Falling-tone ELF/VLF emissions were observed with their rate of frequency change varying from 0.7 to 0.05 kHz/s over 10 min. Bursty-patch emissions in the lower and upper frequency bands are often observed during magnetically disturbed periods. Clear systematic correlation between these various ELF/VLF emissions and cosmic noise absorption was not obtained throughout the campaign period. These observations indicate several previously unknown features of ELF/VLF emissions in subauroral latitudes and demonstrate the importance of continuous measurements for monitoring temporal variations in these emissions. Shiokawa, Kazuo; Yokoyama, Yu; Ieda, Akimasa; Miyoshi, Yoshizumi; Nomura, Reiko; Lee, Sungeun; Sunagawa, Naoki; Miyashita, Yukinaga; Ozaki, Mitsunori; Ishizaka, Kazumasa; Yagitani, Satoshi; Kataoka, Ryuho; Tsuchiya, Fuminori; Schofield, Ian; Connors, Martin; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.910.1002/2014JA020161 Chorus; ELF/VLF; Radiation belts; subauroral latitudes; wave-particle interactions |
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Magnetospheric Multiscale Science Mission Profile and Operations The Magnetospheric Multiscale (MMS) mission and operations are designed to provide the maximum reconnection science. The mission phases are chosen to investigate reconnection at the dayside magnetopause and in the magnetotail. At the dayside, the MMS orbits are chosen to maximize encounters with the magnetopause in regions where the probability of encountering the reconnection diffusion region is high. In the magnetotail, the orbits are chosen to maximize encounters with the neutral sheet, where reconnection is known to occur episodically. Although this targeting is limited by engineering constraints such as total available fuel, high science return orbits exist for launch dates over most of the year. The tetrahedral spacecraft formation has variable spacing to determine the optimum separations for the reconnection regions at the magnetopause and in the magnetotail. In the specific science regions of interest, the spacecraft are operated in a fast survey mode with continuous acquisition of burst mode data. Later, burst mode triggers and a ground-based scientist in the loop are used to determine the highest quality data to downlink for analysis. This operations scheme maximizes the science return for the mission. Space Science Reviews Space Science Reviews Look Fuselier, S.; Lewis, W.; Schiff, C.; Ergun, R.; Burch, J.; Petrinec, S.; Trattner, K.; Published by: Space Science Reviews Published on: 09/2014 YEAR: 2014 DOI: 10.1007/s11214-014-0087-x Magnetic reconnection; Magnetospheric multiscale; Space mission design; Spacecraft orbits |
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Magnetospheric Multiscale Science Mission Profile and Operations The Magnetospheric Multiscale (MMS) mission and operations are designed to provide the maximum reconnection science. The mission phases are chosen to investigate reconnection at the dayside magnetopause and in the magnetotail. At the dayside, the MMS orbits are chosen to maximize encounters with the magnetopause in regions where the probability of encountering the reconnection diffusion region is high. In the magnetotail, the orbits are chosen to maximize encounters with the neutral sheet, where reconnection is known to occur episodically. Although this targeting is limited by engineering constraints such as total available fuel, high science return orbits exist for launch dates over most of the year. The tetrahedral spacecraft formation has variable spacing to determine the optimum separations for the reconnection regions at the magnetopause and in the magnetotail. In the specific science regions of interest, the spacecraft are operated in a fast survey mode with continuous acquisition of burst mode data. Later, burst mode triggers and a ground-based scientist in the loop are used to determine the highest quality data to downlink for analysis. This operations scheme maximizes the science return for the mission. Space Science Reviews Space Science Reviews Look Fuselier, S.; Lewis, W.; Schiff, C.; Ergun, R.; Burch, J.; Petrinec, S.; Trattner, K.; Published by: Space Science Reviews Published on: 09/2014 YEAR: 2014 DOI: 10.1007/s11214-014-0087-x Magnetic reconnection; Magnetospheric multiscale; Space mission design; Spacecraft orbits |
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Magnetospheric Multiscale Science Mission Profile and Operations The Magnetospheric Multiscale (MMS) mission and operations are designed to provide the maximum reconnection science. The mission phases are chosen to investigate reconnection at the dayside magnetopause and in the magnetotail. At the dayside, the MMS orbits are chosen to maximize encounters with the magnetopause in regions where the probability of encountering the reconnection diffusion region is high. In the magnetotail, the orbits are chosen to maximize encounters with the neutral sheet, where reconnection is known to occur episodically. Although this targeting is limited by engineering constraints such as total available fuel, high science return orbits exist for launch dates over most of the year. The tetrahedral spacecraft formation has variable spacing to determine the optimum separations for the reconnection regions at the magnetopause and in the magnetotail. In the specific science regions of interest, the spacecraft are operated in a fast survey mode with continuous acquisition of burst mode data. Later, burst mode triggers and a ground-based scientist in the loop are used to determine the highest quality data to downlink for analysis. This operations scheme maximizes the science return for the mission. Space Science Reviews Space Science Reviews Look Fuselier, S.; Lewis, W.; Schiff, C.; Ergun, R.; Burch, J.; Petrinec, S.; Trattner, K.; Published by: Space Science Reviews Published on: 09/2014 YEAR: 2014 DOI: 10.1007/s11214-014-0087-x Magnetic reconnection; Magnetospheric multiscale; Space mission design; Spacecraft orbits |
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Various scientific applications and services increasingly demand real-time information on the effects of space weather on Earth\textquoterights atmosphere. In this frame, the Royal Observatory of Belgium (ROB) takes advantage of the dense EUREF Permanent GNSS Network (EPN) to monitor the ionosphere over Europe from the measured delays in the GNSS signals, and provides publicly several derived products. The main ROB products consist of ionospheric vertical Total Electron Content (TEC) maps over Europe and their variability estimated in near real-time every 15 min on 0.5\textdegree \texttimes 0.5\textdegree grids using GPS observations. The maps are available online with a latency of ~3 min in IONEX format at ftp://gnss.oma.be and as interactive web pages at www.gnss.be. This paper presents the method used in the ROB-IONO software to generate the maps. The ROB-TEC maps show a good agreement with widely used post-processed products such as IGS and ESA with mean differences of 1.3 \textpm 0.9 and 0.4 \textpm 1.6 TECu respectively for the period 2012 to mid-2013. In addition, we tested the reliability of the ROB-IONO software to detect abnormal ionospheric activity during the Halloween 2003 ionospheric storm. For this period, the mean differences with IGS and ESA maps are 0.9 \textpm 2.2 and 0.6 \textpm 6.8 TECu respectively with maximum differences (>38 TECu) occurring during the major phase of the storm. These differences are due to the lower resolution in time and space of both IGS and ESA maps compared to the ROB-TEC maps. A description of two recent events, one on March 17, 2013 and one on February 27, 2014 also highlights the capability of the method adopted in the ROB-IONO software to detect in near real-time abnormal ionospheric behaviour over Europe. In that frame, ROB maintains a data base publicly available with identified ionospheric events since 2012. Bergeot, Nicolas; Chevalier, Jean-Marie; Bruyninx, Carine; Pottiaux, Eric; Aerts, Wim; Baire, Quentin; Legrand, Juliette; Defraigne, Pascale; Huang, Wei; Published by: Journal of Space Weather and Space Climate Published on: 09/2014 YEAR: 2014 DOI: 10.1051/swsc/2014028 |
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Many solar wind and magnetosphere parameters correlate with relativistic electron flux following storms. These include relativistic electron flux before the storm; seed electron flux; solar wind velocity and number density (and their variation); interplanetary magnetic field Bz, AE and Kp indices; and ultra low frequency (ULF) and very low frequency (VLF) wave power. However, as all these variables are intercorrelated, we use multiple regression analyses to determine which are the most predictive of flux when other variables are controlled. Using 219 storms (1992\textendash2002), we obtained hourly averaged electron fluxes for outer radiation belt relativistic electrons (>1.5 MeV) and seed electrons (100 keV) from Los Alamos National Laboratory spacecraft (geosynchronous orbit). For each storm, we found the log10 maximum relativistic electron flux 48\textendash120 h after the end of the main phase of each storm. Each predictor variable was averaged over the 12 h before the storm, the main phase, and the 48 h following minimum Dst. High levels of flux following storms are best modeled by a set of variables. In decreasing influence, ULF, seed electron flux, Vsw and its variation, and after-storm Bz were the most significant explanatory variables. Kp can be added to the model, but it adds no further explanatory power. Although we included ground-based VLF power from Halley, Antarctica, it shows little predictive ability. We produced predictive models using the coefficients from the regression models and assessed their effectiveness in predicting novel observations. The correlation between observed values and those predicted by these empirical models ranged from 0.645 to 0.795. Simms, Laura; Pilipenko, Viacheslav; Engebretson, Mark; Reeves, Geoffrey; Smith, A.; Clilverd, Mark; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.910.1002/2014JA019955 empirical modeling; multiple regression; multivariable analysis |
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Energetic particle transport into the inner magnetosphere during geomagnetic storms is responsible for significant plasma pressure enhancement, which is the driver of large-scale currents that control the global electrodynamics within the magnetosphere-ionosphere system. Therefore, understanding the transport of plasma from the tail deep into the near-Earth magnetosphere, as well as the energization processes associated with this transport, is essential for a comprehensive knowledge of the near-Earth space environment. During the main phase of a geomagnetic storm on March 17th 2013 (minimum Dst ~ -137 nT), the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument on the Van Allen Probes observed frequent, small-scale proton injections deep into the inner nightside magnetosphere in the region L ~ 4 \textendash 6. Although isolated injections have been previously reported inside geosynchronous orbit, the large number of small-scale injections observed in this event suggests that, during geomagnetic storms injections provide a robust mechanism for transporting energetic ions deep into the inner magnetosphere. In order to understand the role that these injections play in the ring current dynamics, we determine the following properties for each injection: i) associated pressure enhancement, ii) the time duration of this enhancement, iii) and the lowest and highest energy channels exhibiting a sharp increase in their intensities. Based on these properties, we estimate the effect of these small-scale injections on the pressure buildup during the storm. We find that this mode of transport could make a substantial contribution to the total energy gain in the storm-time inner magnetosphere. Gkioulidou, Matina; Ukhorskiy, A.; Mitchell, D.; Sotirelis, T.; Mauk, B.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/2014JA020096 Geomagnetic storms; Ion injections; ring current; Van Allen Probes |
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Simulation of Van Allen Probes Plasmapause Encounters We use an E \texttimes B-driven plasmapause test particle (PTP) simulation to provide global contextual information for in situ measurements by the Van Allen Probes (RBSP) during 15\textendash20 January 2013. During 120 h of simulation time beginning on 15 January, geomagnetic activity produced three plumes. The third and largest simulated plume formed during enhanced convection on 17 January, and survived as a rotating, wrapped, residual plume for tens of hours. To validate the simulation, we compare its output with RBSP data. Virtual RBSP satellites recorded 28 virtual plasmapause encounters during 15\textendash19 January. For 26 of 28 (92\%) virtual crossings, there were corresponding actual RBSP encounters with plasmapause density gradients. The mean difference in encounter time between model and data is 36 min. The mean model-data difference in radial location is 0:40\textpm0:05 RE. The model-data agreement is better for strong convection than for quiet or weakly disturbed conditions. On 18 January, both RBSP spacecraft crossed a tenuous, detached plasma feature at approximately the same time and nightside location as a wrapped residual plume, predicted by the model to have formed 32 h earlier on 17 January. The agreement between simulation and data indicates that the model-provided global information is adequate to correctly interpret the RBSP density observations. Goldstein, J.; De Pascuale, S.; Kletzing, C.; Kurth, W.; Genestreti, K.; Skoug, R.; Larsen, B.; Kistler, L.; Mouikis, C.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/2014JA020252 observations; plasmasphere; residual plume; simulation; Van Allen Probes |
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Simulation of Van Allen Probes Plasmapause Encounters We use an E \texttimes B-driven plasmapause test particle (PTP) simulation to provide global contextual information for in situ measurements by the Van Allen Probes (RBSP) during 15\textendash20 January 2013. During 120 h of simulation time beginning on 15 January, geomagnetic activity produced three plumes. The third and largest simulated plume formed during enhanced convection on 17 January, and survived as a rotating, wrapped, residual plume for tens of hours. To validate the simulation, we compare its output with RBSP data. Virtual RBSP satellites recorded 28 virtual plasmapause encounters during 15\textendash19 January. For 26 of 28 (92\%) virtual crossings, there were corresponding actual RBSP encounters with plasmapause density gradients. The mean difference in encounter time between model and data is 36 min. The mean model-data difference in radial location is 0:40\textpm0:05 RE. The model-data agreement is better for strong convection than for quiet or weakly disturbed conditions. On 18 January, both RBSP spacecraft crossed a tenuous, detached plasma feature at approximately the same time and nightside location as a wrapped residual plume, predicted by the model to have formed 32 h earlier on 17 January. The agreement between simulation and data indicates that the model-provided global information is adequate to correctly interpret the RBSP density observations. Goldstein, J.; De Pascuale, S.; Kletzing, C.; Kurth, W.; Genestreti, K.; Skoug, R.; Larsen, B.; Kistler, L.; Mouikis, C.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/2014JA020252 observations; plasmasphere; residual plume; simulation; Van Allen Probes |
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Three-dimensional stochastic modeling of radiation belts in adiabatic invariant coordinates A 3-D model for solving the radiation belt diffusion equation in adiabatic invariant coordinates has been developed and tested. The model, named Radbelt Electron Model, obtains a probabilistic solution by solving a set of It\^o stochastic differential equations that are mathematically equivalent to the diffusion equation. This method is capable of solving diffusion equations with a full 3-D diffusion tensor, including the radial-local cross diffusion components. The correct form of the boundary condition at equatorial pitch angle α0=90\textdegree is also derived. The model is applied to a simulation of the October 2002 storm event. At α0 near 90\textdegree, our results are quantitatively consistent with GPS observations of phase space density (PSD) increases, suggesting dominance of radial diffusion; at smaller α0, the observed PSD increases are overestimated by the model, possibly due to the α0-independent radial diffusion coefficients, or to insufficient electron loss in the model, or both. Statistical analysis of the stochastic processes provides further insights into the diffusion processes, showing distinctive electron source distributions with and without local acceleration. Zheng, Liheng; Chan, Anthony; Albert, Jay; Elkington, Scot; Koller, Josef; Horne, Richard; Glauert, Sarah; Meredith, Nigel; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.910.1002/2014JA020127 adiabatic invariant coordinates; diffusion equation; fully 3-D model; Radiation belt; stochastic differential equation |
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The trapping of equatorial magnetosonic waves in the Earth\textquoterights outer plasmasphere We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth\textquoterights plasmasphere. Intense equatorial magnetosonic waves were observed inside the plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosonic wave event, we demonstrate that magnetosonic waves can also be trapped within local density structures. We suggest that perpendicular wave propagation is important for explaining the presence of magnetosonic waves in the Earth\textquoterights plasmasphere at locations away from the generation region. Ma, Q.; Li, W.; Chen, L.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Reeves, G.; Henderson, M.; Spence, H.; Published by: Geophysical Research Letters Published on: 09/2014 YEAR: 2014 DOI: 10.1002/2014GL061414 magnetosonic waves; Van Allen Probes; wave excitation; wave propagation |
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The trapping of equatorial magnetosonic waves in the Earth\textquoterights outer plasmasphere We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth\textquoterights plasmasphere. Intense equatorial magnetosonic waves were observed inside the plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosonic wave event, we demonstrate that magnetosonic waves can also be trapped within local density structures. We suggest that perpendicular wave propagation is important for explaining the presence of magnetosonic waves in the Earth\textquoterights plasmasphere at locations away from the generation region. Ma, Q.; Li, W.; Chen, L.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Reeves, G.; Henderson, M.; Spence, H.; Published by: Geophysical Research Letters Published on: 09/2014 YEAR: 2014 DOI: 10.1002/2014GL061414 magnetosonic waves; Van Allen Probes; wave excitation; wave propagation |
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Acceleration and loss driven by VLF chorus: Van Allen Probes observations and DREAM model results For over a decade now we have understood the response of the Earth\textquoterights radiation belts to solar wind driving are a delicate balance of acceleration and loss processes. Theory has shown that the interaction of relativistic electrons with VLF whistler mode chorus can produce both energization through momentum diffusion and loss through pitch angle diffusion. Recent results from the Van Allen Probes mission has confirmed observationally that chorus can produce both acceleration and loss. The Van Allen Probes satellites are able to measure all the critical particle populations and wave fields with unprecedented precision and resolution but only at the two spacecraft locations. Those spatially-localized observations can be extended globally using three-dimensional diffusion codes such as the DREAM model. We will discuss some of the recent Van Allen Probes observations that firmly demonstrate local acceleration by chorus and losses due to chorus-produced pitch angle scattering (as well as outward radial diffusion). We will look at observational evidence for the complex chain of processes that inject a \textquotedblleftseed population\textquotedblright, generate chorus, and ultimately drive radiation belt acceleration and loss. We will also discuss how local satellite observations can be generalized to simulate global dynamics using data-driven input and boundary conditions. RW1/J/IEIE0175/0001 Reeves, G.; Spence, H.; Henderson, M.; Tu, W.; Cunningham, G.; Chen, Y.; Blake, J.; Fennell, J.; Baker, D.; Published by: Published on: 08/2014 YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929879 |
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Acceleration and loss driven by VLF chorus: Van Allen Probes observations and DREAM model results For over a decade now we have understood the response of the Earth\textquoterights radiation belts to solar wind driving are a delicate balance of acceleration and loss processes. Theory has shown that the interaction of relativistic electrons with VLF whistler mode chorus can produce both energization through momentum diffusion and loss through pitch angle diffusion. Recent results from the Van Allen Probes mission has confirmed observationally that chorus can produce both acceleration and loss. The Van Allen Probes satellites are able to measure all the critical particle populations and wave fields with unprecedented precision and resolution but only at the two spacecraft locations. Those spatially-localized observations can be extended globally using three-dimensional diffusion codes such as the DREAM model. We will discuss some of the recent Van Allen Probes observations that firmly demonstrate local acceleration by chorus and losses due to chorus-produced pitch angle scattering (as well as outward radial diffusion). We will look at observational evidence for the complex chain of processes that inject a \textquotedblleftseed population\textquotedblright, generate chorus, and ultimately drive radiation belt acceleration and loss. We will also discuss how local satellite observations can be generalized to simulate global dynamics using data-driven input and boundary conditions. RW1/J/IEIE0175/0001 Reeves, G.; Spence, H.; Henderson, M.; Tu, W.; Cunningham, G.; Chen, Y.; Blake, J.; Fennell, J.; Baker, D.; Published by: Published on: 08/2014 YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929879 |
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Acceleration and loss driven by VLF chorus: Van Allen Probes observations and DREAM model results For over a decade now we have understood the response of the Earth\textquoterights radiation belts to solar wind driving are a delicate balance of acceleration and loss processes. Theory has shown that the interaction of relativistic electrons with VLF whistler mode chorus can produce both energization through momentum diffusion and loss through pitch angle diffusion. Recent results from the Van Allen Probes mission has confirmed observationally that chorus can produce both acceleration and loss. The Van Allen Probes satellites are able to measure all the critical particle populations and wave fields with unprecedented precision and resolution but only at the two spacecraft locations. Those spatially-localized observations can be extended globally using three-dimensional diffusion codes such as the DREAM model. We will discuss some of the recent Van Allen Probes observations that firmly demonstrate local acceleration by chorus and losses due to chorus-produced pitch angle scattering (as well as outward radial diffusion). We will look at observational evidence for the complex chain of processes that inject a \textquotedblleftseed population\textquotedblright, generate chorus, and ultimately drive radiation belt acceleration and loss. We will also discuss how local satellite observations can be generalized to simulate global dynamics using data-driven input and boundary conditions. RW1/J/IEIE0175/0001 Reeves, G.; Spence, H.; Henderson, M.; Tu, W.; Cunningham, G.; Chen, Y.; Blake, J.; Fennell, J.; Baker, D.; Published by: Published on: 08/2014 YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929879 |
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Comparison of Energetic Electron Intensities Outside and Inside the Radiation Belts The intensities of energetic electrons (~25 \textendash 800 keV) outside and inside Earth\textquoterights radiation belts are reported using measurements from THEMIS and Van Allen Probes during non-geomagnetic storm periods. Three intervals of current disruption/dipolarization events in August, 2013 were selected for comparison. The following results are obtained. (1) Phase space densities (PSDs) for the equatorially mirroring electron population at three values of the first adiabatic invariant (20, 70, and 200 MeV/G) at the outer radiation belt boundary are found to be one to three orders of magnitude higher than values measured just inside the radiation belt. (2) There is indication that substorm activity leads to PSD increases inside L = 5.5 in less than 1 hr. (3) Evidence for progressive inward transport of enhanced PSDs is found. (4) Reductions and enhancements in the PSDs over L-shells from 3.5 to 6 are found to occur rapidly in ~2 \textendash 3 hrs. These results suggest that (1) continual replenishments are required to maintain high levels of PSD for electrons at these energies, and (2) inward radial transport of these electrons occurs in a fast time scale of a few hrs. T. Y. Lui, A.; Mitchell, D.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2014JA020049 Dipolarization; energetic electrons; Radiation belts; substorm; Van Allen Probes |
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Measurements from the Polar-Orbiting Environmental Satellite (POES) Medium Energy Proton and Electron Detector (MEPED) instrument are widely used in studies into radiation belt dynamics and atmospheric coupling. However, this instrument has been shown to have a complex energy-dependent response to incident particle fluxes, with the additional possibility of low-energy protons contaminating the electron fluxes. We test the recent Monte Carlo theoretical simulation of the instrument by comparing the responses against observations from an independent experimental data set. Our study examines the reported geometric factors for the MEPED electron flux instrument against the high-energy resolution Instrument for Detecting Particles (IDPs) on the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions satellite when they are located at similar locations and times, thereby viewing the same quasi-trapped population of electrons. We find that the new Monte Carlo-produced geometric factors accurately describe the response of the POES MEPED instrument. We go on to develop a set of equations such that integral electron fluxes of a higher accuracy are obtained from the existing MEPED observations. These new MEPED integral fluxes correlated very well with those from the IDP instrument (>99.9\% confidence level). As part of this study we have also tested a commonly used algorithm for removing proton contamination from MEPED instrument observations. We show that the algorithm is effective, providing confirmation that previous work using this correction method is valid. Whittaker, Ian; Rodger, Craig; Clilverd, Mark; Sauvaud, \; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2014JA020021 DEMETER; energetic electron flux; geometric factor; POES; Radiation belts |
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We present first results from a study of the plasma instability mechanism responsible for the small-scale (\~10 m) ionospheric density irregularities commonly observed by the Super Dual Auroral Radar Network (SuperDARN) HF radars in the vicinity of Sub Auroral Polarization Streams (SAPS) during periods of geomagnetic disturbance. A focus is placed on the mid-latitude region of the ionosphere over North America where recent expansion of the SuperDARN network allows for extensive direct comparisons with total electron content (TEC) measurements from a dense network of ground-based GPS receivers. The TEC observations indicate that high-speed SAPS channels and the associated small-scale irregularities are typically located within the mid-latitude ionospheric trough. The Millstone Hill Incoherent Scatter Radar (ISR), operating in campaign mode in support of the NASA Van Allen Probes mission, provided measurements of F region ion/electron density, velocity, and temperature suitable for identifying potential mechanisms of plasma instability during a SAPS event that extended over 12 hours of magnetic local time (MLT) on 2 February 2013. Previous work has indicated that the density gradients associated with the poleward wall of the mid-latitude trough can produce small-scale irregularities due to the gradient drift instability during quiet periods by cascade from larger-scale structures. In this study we demonstrate that the gradient drift instability is a viable source for the direct generation of the small-scale irregularities observed by SuperDARN radars in the mid-latitude ionosphere during geomagnetically disturbed conditions. Thomas, Evan; Yan, Jingye; Zhang, Jiaojiao; Baker, Joseph; Ruohoniemi, Michael; Hoskawa, Keisuke; Erickson, Philip; Coster, Anthea; Foster, John; Published by: Published on: 08/2014 YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929853 |
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We present first results from a study of the plasma instability mechanism responsible for the small-scale (\~10 m) ionospheric density irregularities commonly observed by the Super Dual Auroral Radar Network (SuperDARN) HF radars in the vicinity of Sub Auroral Polarization Streams (SAPS) during periods of geomagnetic disturbance. A focus is placed on the mid-latitude region of the ionosphere over North America where recent expansion of the SuperDARN network allows for extensive direct comparisons with total electron content (TEC) measurements from a dense network of ground-based GPS receivers. The TEC observations indicate that high-speed SAPS channels and the associated small-scale irregularities are typically located within the mid-latitude ionospheric trough. The Millstone Hill Incoherent Scatter Radar (ISR), operating in campaign mode in support of the NASA Van Allen Probes mission, provided measurements of F region ion/electron density, velocity, and temperature suitable for identifying potential mechanisms of plasma instability during a SAPS event that extended over 12 hours of magnetic local time (MLT) on 2 February 2013. Previous work has indicated that the density gradients associated with the poleward wall of the mid-latitude trough can produce small-scale irregularities due to the gradient drift instability during quiet periods by cascade from larger-scale structures. In this study we demonstrate that the gradient drift instability is a viable source for the direct generation of the small-scale irregularities observed by SuperDARN radars in the mid-latitude ionosphere during geomagnetically disturbed conditions. Thomas, Evan; Yan, Jingye; Zhang, Jiaojiao; Baker, Joseph; Ruohoniemi, Michael; Hoskawa, Keisuke; Erickson, Philip; Coster, Anthea; Foster, John; Published by: Published on: 08/2014 YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929853 |
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Fast transport of resonant electrons in phase space due to nonlinear trapping by whistler waves We present an analytical, simplified formulation accounting for the fast transport of relativistic electrons in phase space due to wave-particle resonant interactions in the inhomogeneous magnetic field of Earth\textquoterights radiation belts. We show that the usual description of the evolution of the particle velocity distribution based on the Fokker-Planck equation can be modified to incorporate nonlinear processes of wave-particle interaction, including particle trapping. Such a modification consists in one additional operator describing fast particle jumps in phase space. The proposed, general approach is used to describe the acceleration of relativistic electrons by oblique whistler waves in the radiation belts. We demonstrate that for a wave power distribution with a hard enough power law tail inline image such that η < 5/2, the efficiency of nonlinear acceleration could be more effective than the conventional quasi-linear acceleration for 100 keV electrons. Artemyev, A.; Vasiliev, A.; Mourenas, D.; Agapitov, O.; Krasnoselskikh, V.; Boscher, D.; Rolland, G.; Published by: Geophysical Research Letters Published on: 08/2014 YEAR: 2014 DOI: 10.1002/grl.v41.1610.1002/2014GL061380 particle trapping; Radiation belts; Wave-particle interaction |
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Generation of Unusually Low Frequency Plasmaspheric Hiss It has been reported from Van Allen Probe observations that plasmaspheric hiss intensification in the outer plasmasphere, associated with a substorm injection on Sept 30 2012, occurred with a peak frequency near 100 Hz, well below the typical plasmaspheric hiss frequency range, extending down to ~20 Hz. We examine this event of unusually low frequency plasmaspheric hiss to understand its generation mechanism. Quantitative analysis is performed by simulating wave ray paths via the HOTRAY ray tracing code with measured plasma density and calculating ray path-integrated wave gain evaluated using the measured energetic electron distribution. We demonstrate that the growth rate due to substorm injected electrons is positive but rather weak, leading to small wave gain (~10 dB) during a single equatorial crossing. Propagation characteristics aided by the sharp density gradient associated with the plasmapause, however, can enable these low frequency waves to undergo cyclic ray paths, which return to the unstable region leading to repeated amplification to yield sufficient net wave gain (>40 dB) to allow waves to grow from the thermal noise. Chen, Lunjin; Thorne, Richard; Bortnik, Jacob; Li, Wen; Horne, Richard; Reeves, G.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Blake, J.; Fennell, J.; Published by: Geophysical Research Letters Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2014GL060628 Chorus; Generation; Plasmaspheric Hiss; Ray Tracing; Van Allen Probes |
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Generation of Unusually Low Frequency Plasmaspheric Hiss It has been reported from Van Allen Probe observations that plasmaspheric hiss intensification in the outer plasmasphere, associated with a substorm injection on Sept 30 2012, occurred with a peak frequency near 100 Hz, well below the typical plasmaspheric hiss frequency range, extending down to ~20 Hz. We examine this event of unusually low frequency plasmaspheric hiss to understand its generation mechanism. Quantitative analysis is performed by simulating wave ray paths via the HOTRAY ray tracing code with measured plasma density and calculating ray path-integrated wave gain evaluated using the measured energetic electron distribution. We demonstrate that the growth rate due to substorm injected electrons is positive but rather weak, leading to small wave gain (~10 dB) during a single equatorial crossing. Propagation characteristics aided by the sharp density gradient associated with the plasmapause, however, can enable these low frequency waves to undergo cyclic ray paths, which return to the unstable region leading to repeated amplification to yield sufficient net wave gain (>40 dB) to allow waves to grow from the thermal noise. Chen, Lunjin; Thorne, Richard; Bortnik, Jacob; Li, Wen; Horne, Richard; Reeves, G.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Blake, J.; Fennell, J.; Published by: Geophysical Research Letters Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2014GL060628 Chorus; Generation; Plasmaspheric Hiss; Ray Tracing; Van Allen Probes |
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The Sub-Auroral Polarization Stream (SAPS) is a geospace boundary layer phenomenon associated with the interaction of the warm plasma of the magnetospheric ring current with the cold ions and electrons of the outer plasmasphere [1]. Driven by ring current enhancements during magnetospheric disturbances, SAPS location, intensity, and characteristics are greatly influenced by the underlying ionosphere. Strong M-I coupling by means of field-aligned currents creates a high-speed (>1000 m/s) westward plasma flow channel in the ionosphere at pre-midnight/post-noon local times which is readily observable by incoherent scatter [2] and HF radars and in plasma drift observations by low-altitude spacecraft (e.g. DMSP). The fast ionospheric flows generate E-region irregularities providing for additional diagnostics using coherent backscatter techniques [3]. SAPS plays a significant role in the redistribution of cold plasma through the geospace system at both ionospheric and magnetospheric heights. Where the SAPS flow channel overlaps the mid-latitude ionosphere and outer plasmasphere, streams of cold plasma are carried westward and sunward as plumes of storm enhanced density (SED) in the ionosphere and as plasmasphere erosion plumes at high altitude. Ground-based maps of GPS total electron content (TEC) serve to visualize the spatial extent and evolution of the SAPS and SED. Mapping these features to magnetospheric altitudes along magnetic field lines permits direct intercomparison with in situ spacecraft observations. The recently launched Van Allen Probes twin satellites (RBSP-A \& RBSP-B) are in near-equatorial orbits well suited for studies of the SAPS and related phenomena at the apex of field lines threading the plasmasphere boundary layer. Simultaneous near magnetic field aligned observations of SAPS at DMSP altitude (\~800 km) and by RBSP-A at \~20,000 km show close correspondence of SAPS location and characteristics between the ionosphere and- magnetosphere. In highly elliptical orbits with apogee near 5.5 Re, the RBSP spacecraft often spend hours at a time skimming the outer plasmasphere within the SAPS region. A great variety of wave phenomena are observed. Here we describe long-duration large amplitude (+/- 5 mV/m) electric field oscillations with 3 min\textendash5 min period seen in the magnetospheric equatorial plane within the SAPS/erosion plume region. Foster, John; Erickson, Philip; Published by: Published on: 08/2014 YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929852 |
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Observations of the inner radiation belt: CRAND and trapped solar protons Measurements of inner radiation belt protons have been made by the Van Allen Probes Relativistic Electron-Proton Telescopes as a function of kinetic energy (24 to 76 MeV), equatorial pitch angle, and magnetic L shell, during late-2013 and early-2014. A probabilistic data analysis method reduces background from contamination by higher energy protons. Resulting proton intensities are compared to predictions of a theoretical radiation belt model. Then trapped protons originating both from cosmic ray albedo neutron decay (CRAND) and from trapping of solar protons are evident in the measured distributions. An observed double-peaked distribution in L is attributed, based on the model comparison, to a gap in the occurrence of solar proton events during the 2007 to 2011 solar minimum. Equatorial pitch angle distributions show that trapped solar protons are confined near the magnetic equator, but that CRAND protons can reach low-altitudes. Narrow pitch angle distributions near the outer edge of the inner belt are characteristic of proton trapping limits. Selesnick, R.; Baker, D.; Jaynes, A.; Li, X.; Kanekal, S.; Hudson, M.; Kress, B.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2014JA020188 |
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Prompt energization of relativistic and highly relativistic electrons during a substorm interval On 17 March 2013, a large magnetic storm significantly depleted the multi-MeV radiation belt. We present multi-instrument observations from the Van Allen Probes spacecraft Radiation Belt Storm Probe A and Radiation Belt Storm Probe B at \~6 Re in the midnight sector magnetosphere and from ground-based ionospheric sensors during a substorm dipolarization followed by rapid reenergization of multi-MeV electrons [1]. A 50\% increase in magnetic field magnitude occurred simultaneously with dramatic increases in 100 keV electron fluxes and a 100 times increase in VLF wave intensity. Chorus is excited following the injection of low-energy (1\textendash30 keV) plasma sheet electrons into the inner magnetosphere [2]. During the 17 March substorm injection, cold plasma that had circulated into the nightside magnetosphere from the dayside ionosphere-plasmasphere contributed to an energetic (50 keV) electron population involved in chorus-mode wave amplification [3]. The high-energy tail (>100 keV) of the injected electrons and the intense VLF waves provide a seed population and energy source for subsequent radiation belt energization. The observed electron flux behavior is striking in its large increases over short intervals. As seen by RBSP-A at L* \~ 4.5 highly relativistic (>2MeV) electron fluxes increased immediately at the time of the substorm injection and strong chorus enhancement. At RBSP-B, at apogee at substorm onset, observed in the \~5 h separation between L* = 4.0 crossings, 3.60 MeV highly relativistic electron fluxes increased by a factor of 56, while 4.50 MeV flux increased by an even larger factor of 95. The 17 March multipoint observations indicate the significant role that substorm processes can play in creating a seed population of 100 keV electrons and VLF chorus wave enhancements that can lead to a prompt energization of relativistic and highly relativistic electrons in the region outside the plasm- pause. Foster, John; Erickson, Philip; Published by: Published on: 08/2014 YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929876 Magnetic flux; Magnetosphere; Van Allen Belts; Van Allen Probes |