The Experts below are selected from a list of 4863 Experts worldwide ranked by ideXlab platform
M H Denton - One of the best experts on this subject based on the ideXlab platform.
-
an improved empirical model of electron and ion fluxes at Geosynchronous Orbit based on upstream solar wind conditions
Social Work, 2016Co-Authors: M F Thomsen, Joseph E Borovsky, M H Denton, M G Henderson, V K Jordanova, J R Woodroffe, D P Hartley, D PitchfordAbstract:In this study, a new empirical model of the electron fluxes and ion fluxes at Geosynchronous Orbit (GEO) is introduced, based on observations by Los Alamos National Laboratory (LANL) satellites. The model provides flux predictions in the energy range ~1 eV to ~40 keV, as a function of local time, energy, and the strength of the solar wind electric field (the negative product of the solar wind speed and the z component of the magnetic field). Given appropriate upstream solar wind measurements, the model provides a forecast of the fluxes at GEO with a ~1 h lead time. Model predictions are tested against in-sample observations from LANL satellites and also against out-of-sample observations from the Compact Environmental Anomaly Sensor II detector on the AMC-12 satellite. The model does not reproduce all structure seen in the observations. However, for the intervals studied here (quiet and storm times) the normalized root-mean-square deviation < ~0.3. It is intended that the model will improve forecasting of the spacecraft environment at GEO and also provide improved boundary/input conditions for physical models of the magnetosphere.
-
the proton and electron radiation belts at Geosynchronous Orbit statistics and behavior during high speed stream driven storms
Journal of Geophysical Research, 2016Co-Authors: T E Cayton, M H Denton, R D Belian, Roderick A Christensen, Charles J IngrahamAbstract:The outer proton radiation belt (OPRB) and outer electron radiation belt (OERB) at Geosynchronous Orbit are investigated using a reanalysis of the LANL CPA (Charged Particle Analyzer) 8-satellite 2-solar cycle energetic particle data set from 1976 to 1995. Statistics of the OPRB and the OERB are calculated, including local time and solar cycle trends. The number density of the OPRB is about 10 times higher than the OERB, but the 1 MeV proton flux is about 1000 times less than the 1 MeV electron flux because the proton energy spectrum is softer than the electron spectrum. Using a collection of 94 high-speed stream-driven storms in 1976–1995, the storm time evolutions of the OPRB and OERB are studied via superposed epoch analysis. The evolution of the OERB shows the familiar sequence (1) prestorm decay of density and flux, (2) early-storm dropout of density and flux, (3) sudden recovery of density, and (4) steady storm time heating to high fluxes. The evolution of the OPRB shows a sudden enhancement of density and flux early in the storm. The absence of a proton dropout when there is an electron dropout is noted. The sudden recovery of the density of the OERB and the sudden density enhancement of the OPRB are both associated with the occurrence of a substorm during the early stage of the storm when the superdense plasma sheet produces a “strong stretching phase” of the storm. These storm time substorms are seen to inject electrons to 1 MeV and protons to beyond 1 MeV into Geosynchronous Orbit, directly producing a suddenly enhanced radiation belt population.
-
free energy to drive equatorial magnetosonic wave instability at Geosynchronous Orbit
Journal of Geophysical Research, 2011Co-Authors: M F Thomsen, M H Denton, V K Jordanova, Lunjin Chen, R M ThorneAbstract:The magnetosonic (or ion Bernstein) instability is driven by a positive slope in the ion distribution function perpendicular to the magnetic field at energies above about 1 keV. Fifteen years of multisatellite Geosynchronous observations are used to determine the statistical occurrence of ion distributions with positive slopes as a function of energy, local time, geomagnetic activity, and phase of the solar cycle. There is no discernable dependence on phase of the solar cycle, but there are clear dependences on the other parameters. Positive slopes are seen primarily in the energy range between similar to 3 and similar to 24 keV. The peak occurrence of positive slopes is between midmorning and dusk and moves progressively toward earlier local times for higher energies. The occurrence is significantly greater and extends over a broader local time range for low levels of geomagnetic activity than for high activity, for all energies. At high activity levels, the occurrence tends to be more closely confined near noon. Peak occurrence rates are similar to 30% at energies just below 10 keV. A superposed epoch analysis of 77 coronal mass ejection (CME)-driven storms and 93 high-speed solar wind (HSS)-driven storms shows a relative suppression of the occurrence frequency of positive slopes during the recovery phase. The suppression is particularly long-lived for HSS-driven streams.
-
on the heating of the outer radiation belt to produce high fluxes of relativistic electrons measured heating rates at Geosynchronous Orbit for high speed stream driven storms
Journal of Geophysical Research, 2010Co-Authors: Joseph E Borovsky, M H DentonAbstract:[1] The heating rate of the outer electron radiation belt at Geosynchronous Orbit is determined for the interval from 36 to 72 h after the onset of high-speed stream-driven storms. Multisatellite measurements of the radiation belt temperature are used for 93 high-speed stream-driven storms. During the storms, the outer electron radiation belt temperature changes from ∼120 keV to ∼190 keV. The average heating rate of 32 keV d−1 is obtained. The heating rate during the storms is found to be positively correlated with the solar wind velocity and with the Kp index of geomagnetic activity and to be negatively correlated with the solar wind number density. When the solar wind velocity is held fixed, the correlation of the heating rate with Kp vanishes. Expressions for the change in the heating rate as function of the solar wind speed, the solar wind density, and the Kp index are fit to the data. The heating rate is uncorrelated with the amplitude of magnetic field fluctuations in the magnetosphere. Correlations between the heating rate and the level of velocity, density, and magnetic field fluctuations in the magnetosphere and in the solar wind are weaker than the correlations of the heating rate with the solar wind velocity and density. The heating rates correspond to a kinetic energy density change of 3.6 × 10−11 erg cm−3 d−1 at Geosynchronous Orbit, to a specific entropy change of 4.1 × 106 eV cm2 d−1 at Geosynchronous Orbit, and to a total heating rate of the Geosynchronous Orbit region of 5.3 × 106 Watts.
-
magnetic field at Geosynchronous Orbit during high speed stream driven storms connections to the solar wind the plasma sheet and the outer electron radiation belt
Journal of Geophysical Research, 2010Co-Authors: M H DentonAbstract:[1] Superposed-epoch analysis is performed on magnetic field measurements from five GOES spacecraft in Geosynchronous Orbit during 63 high-speed stream-driven storms in 1995–2005. The field strength and the field stretching angle are examined as functions of time and local time, and these quantities are compared with the properties of the solar wind, the plasma sheet, and the outer electron radiation belt. Compression of the dayside magnetosphere coincides with an increased solar wind ram pressure commencing before the arrival of the corotating interaction region (CIR). Stretching of the nightside magnetosphere occurs in two phases: a strong-stretching phase early in the storm followed by a modest-stretching phase lasting for days. The strong-stretching phase coincides with the occurrence of the superdense plasma sheet, implying that ion pressure causes the strong stretching. This nightside strong-stretching perturbation corresponds to a ∼25% contribution to Dst*. The relativistic electron flux at Geosynchronous Orbit has a dropout recovery temporal profile that matches the strong-stretching temporal profile; however, the number density dropout and recovery of the electron radiation belt has a profile that leads the stretching profile. A comparison of Geosynchronous field strengths and magnetopause field strengths indicates that magnetopause shadowing plays a role in the radiation belt dropout. Temporal fluctuations of the Geosynchronous magnetic field are examined via 1 min changes of the GOES magnetic field vectors. Fluctuation amplitudes increase at all local times at storm onset and then slowly decay during the storms. The amplitude is linearly related to the Kp, PCI, and MBI indices, except during the strong-stretching phase of the storms.
H. J. Singer - One of the best experts on this subject based on the ideXlab platform.
-
van allen probes themis goes and cluster observations of emic waves ulf pulsations and an electron flux dropout
Journal of Geophysical Research, 2016Co-Authors: K Sigsbee, C A Kletzing, C W Smith, R J Macdowall, H E Spence, G D Reeves, J B Blake, D N Baker, J C Green, H. J. SingerAbstract:We examined an electron flux dropout during the 12–14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS)-A (P5), Cluster 2, and Geostationary Operational Environmental Satellites (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at Geosynchronous Orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 h from 12 to 14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12–13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ electromagnetic ion cyclotron (EMIC) waves from just inside Geosynchronous Orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13–14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst <–100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finallymore » returned to near prestorm values, possibly in response to strong ultralow frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior.« less
-
diamagnetic oscillations ahead of stopped dipolarization fronts
Journal of Geophysical Research, 2014Co-Authors: A Runov, V Angelopoulos, V A Sergeev, K H Glassmeier, H. J. SingerAbstract:It is well established that fast flows in the magnetotail plasma sheet which are separated from the ambient plasma by dipolarization fronts brake in the tail-dipole transition region. Flow/front braking is suggested to play an important role in generation of compressional waves in the inner magnetosphere and geomagnetic pulsations. Because of the paucity of multipoint observations in the tail-dipole transition region, however, details of wave generation during flow/front braking are unknown. Using comprehensive coverage of the near-Earth plasma sheet and geostationary Orbit by six spacecraft, we explore the relationship between dipolarization fronts that propagated earthward at x=−11 to −9RE and stopped at x=−9 to −8RE and compressional oscillations observed at x≈−8RE. The oscillations, which were diamagnetic (i.e., exhibited antiphase variations in magnetic and plasma pressures), were observed about a minute prior to front detection. The amplitude of the magnetic oscillations at −8RE was ∼5 nT; the wavelength was ∼0.5RE. Enhancements of magnetic oscillations with different frequencies and amplitudes of 1 to 2 and 2 to 4 nT were detected at Geosynchronous Orbit and on the ground, respectively. Analysis of observations reveals that although the fast flow/front stopped a few RE beyond Geosynchronous Orbit, the plasma compression propagated farther inward and excited compressional diamagnetic oscillations in the tail-dipole transition region.
-
emic waves observed at Geosynchronous Orbit during solar minimum statistics and excitation
Journal of Geophysical Research, 2011Co-Authors: L B N Clausen, J B H Baker, J M Ruohoniemi, H. J. SingerAbstract:[1] We identified 1875 wave events in magnetic field data from Geosynchronous Orbit. Most of these events were transverse with respect to the background magnetic field, left-hand polarized, and were observed in the post-noon magnetic local time sector at frequencies just below the helium gyrofrequency. Combined, these observations strongly suggest that most of these events are Electromagnetic Ion Cyclotron (EMIC) waves. Average wave amplitudes are presented, binned by frequency, geomagnetic activity and magnetic local time. The amplitude increases with increasing geomagnetic activity; increased activity also narrows the local time sector in which the waves are observed. A superposed epoch analysis of solar wind parameters and geomagnetic activity indices shows that 12 hours before wave onset the AE and Kp index increased, indicating storm and substorm activity that injects hot ion populations needed to drive the EMIC instability and providing ample time for those populations to drift into the post-noon local time sector. Just before wave onset a sudden enhancement in the AE index and the solar wind dynamic pressure are observed, indicating that a final perturbation of the magnetosphere is needed to excite EMIC wave growth. EMIC waves are thought to cause loss of relativistic particles in the radiation belt. Large solar wind densities have been associated with low flux of relativistic particles during the recovery phase of geomagnetic storms. We show that EMIC waves are preferentially generated during intervals of large solar wind density, indicating that such conditions drive EMIC waves which in turn cause enhanced loss of relativistic particles.
-
solar cycle dependence of bulk ion composition at Geosynchronous Orbit
Journal of Geophysical Research, 2011Co-Authors: R E Denton, K Takahashi, M F Thomsen, R R Anderson, H. J. SingerAbstract:[1] While the average ion mass M (normalized to amu) of bulk plasma at Geosynchronous Orbit has been calculated at solar maximum (during the era of the Combined Release and Radiation Effects Satellite (CRRES)), the solar cycle dependence of bulk ion composition at Geosynchronous Orbit is not known. Here, we use measurements of mass density ρm from Alfven wave frequencies measured by the Geostationary Operational Environmental Satellites and ion density measurements by the Magnetospheric Particle Analyzer (MPA) on Los Alamos National Laboratory (LANL) spacecraft to establish the solar cycle dependence of bulk ion composition. We show that there is a strong correlation between the yearly median value of ρm, ρm,yr−med, and the yearly average of the solar EUV flux F10.7, F10.7,yr−av; log10(ρm,yr−med) ≃ 0.5089 + 0.003607F10.7,yr−av (for ρm values adjusted to a magnetic latitude MLAT of 8°). We calibrate the measurements of the MPA instrument on one spacecraft to those from another by using yearly median density values. Then, using close conjunctions of LANL spacecraft with CRRES (for which we have inferred values of ρm and ne), we calibrate the ideal theoretical value of MPA ion density nMPA−th (the value that MPA would measure if it measured all the ions) to the observed values directly measured by the instrument, nMPA−obs. We find that nMPA−th is approximately 1.47 times the value of nMPA−obs measured by the LANL 1994 spacecraft. Using the yearly median values of ρm as a function of F10.7, the yearly median values of nMPA−th from the MPA instruments, and a model for the concentration of He+, we are able to calculate the solar cycle dependence of the average ion mass M and the O+ concentration ηO+ ≡ nO+/ne. We find that M is typically ∼3.8 at solar maximum and near unity at solar minimum. Typical values of ηO+ vary by 2 orders of magnitude over the solar cycle, from about 0.2 at solar maximum to ∼2 × 10−3 at solar minimum. Furthermore, our results also demonstrate that the typical concentration of He+ must also be very low at solar minimum. Since the median yearly values of density are low, characteristic of the plasma trough, our results are most applicable to that region. Considering, however, that the plasmasphere and plume typically have a low concentration of O+, the concentration of O+ at Geosynchronous Orbit at solar minimum is likely to be low for all conditions (with the possible exception of very low densities for which the high-energy component might dominate).
-
relativistic electron loss due to ultralow frequency waves and enhanced outward radial diffusion
Journal of Geophysical Research, 2010Co-Authors: S R Elkington, H. J. Singer, I. R. Mann, T M Lotoaniu, C L Waters, V Angelopoulos, J W BonnellAbstract:[1] Using the THEMIS and GOES satellites and ground-based magnetometers, the loss of outer zone radiation belt electrons through the magnetopause in response to ultralow frequency (ULF) waves is examined. A 2 orders of magnitude decrease in >2 MeV electron flux observed at Geosynchronous Orbit, starting at 00 UT on 25 June 2008, is attributed to a rapid (1–4 h) nonadiabatic loss process. ULF waves were observed by the THEMIS-A, -D, and -E probes in the afternoon-to-dusk sector from the magnetopause to Geosynchronous altitude. Estimates of the electron resonant energies indicate strong drift resonant interactions occurring between the energetic electrons and the observed waves. The rate of outward radial diffusion was estimated for MeV electrons using the observed ULF wave azimuthal electric field and compressional magnetic field and the diffusion time (∼2.5 h) was found to be in good agreement with the observed time for nonadiabatic flux decreases at Geosynchronous Orbit. The magnetopause was compressed inside of its nominal position because of increased solar wind dynamic pressure. The electron loss is interpreted as a combination of magnetopause shadowing (from the compressed magnetosphere) and enhanced outward diffusion from ULF wave-particle drift resonant interactions. The enhanced day-night asymmetry of the MeV electron drift path from the compression suggests that enhanced losses may have also occurred around local noon as well as in the afternoon-to-dusk sector.
G D Reeves - One of the best experts on this subject based on the ideXlab platform.
-
spatial structure and temporal evolution of energetic particle injections in the inner magnetosphere during the 14 july 2013 substorm event
arXiv: Space Physics, 2016Co-Authors: M Gkioulidou, G D Reeves, D L Turner, A Y Ukhorskiy, S Ohtani, D G Mitchell, J W Gjerloev, M Nose, Kiyokazu Koga, J V RodriguezAbstract:Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside Geosynchronous Orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm $\textit{ Dst }$ $\sim$ -40nT on 14 July 2013. Van Allen Probe B, inside Geosynchronous Orbit, observed two energetic proton injections within 10min, with different dipolarization signatures and duration. The first one is a dispersionless, short-timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer-timescale injection pulse accompanied by a gradual dipolarization signature. We combined ground magnetometer data from various stations and in situ particle and magnetic field data from multiple satellites in the inner magnetosphere and near-Earth plasma sheet to determine the spatial extent of these injections, their temporal evolution, and their effects in the inner magnetosphere. Our results indicate that there are different spatial and temporal scales at which injections can occur in the inner magnetosphere and depict the necessity of multipoint observations of both particle and magnetic field data in order to determine these scales.
-
van allen probes themis goes and cluster observations of emic waves ulf pulsations and an electron flux dropout
Journal of Geophysical Research, 2016Co-Authors: K Sigsbee, C A Kletzing, C W Smith, R J Macdowall, H E Spence, G D Reeves, J B Blake, D N Baker, J C Green, H. J. SingerAbstract:We examined an electron flux dropout during the 12–14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS)-A (P5), Cluster 2, and Geostationary Operational Environmental Satellites (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at Geosynchronous Orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 h from 12 to 14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12–13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ electromagnetic ion cyclotron (EMIC) waves from just inside Geosynchronous Orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13–14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst <–100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finallymore » returned to near prestorm values, possibly in response to strong ultralow frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior.« less
-
analysis of the effectiveness of ground based vlf wave observations for predicting or nowcasting relativistic electron flux at geostationary Orbit
Journal of Geophysical Research, 2015Co-Authors: Laura E Simms, M J Engebretson, A J Smith, Mark A Clilverd, V A Pilipenko, G D ReevesAbstract:Poststorm relativistic electron flux enhancement at Geosynchronous Orbit has shown correlation with very low frequency (VLF) waves measured by satellite in situ. However, our previous study found little correlation between electron flux and VLF measured by a ground-based instrument at Halley, Antarctica. Here we explore several possible explanations for this low correlation. Using 220 storms (1992–2002), our previous work developed a predictive model of the poststorm flux at Geosynchronous Orbit based on explanatory variables measured a day or two before the flux increase. In a nowcast model, we use averages of variables from the time period when flux is rising during the recovery phase of geomagnetic storms and limit the VLF (1.0 kHz) measure to the dawn period at Halley (09:00–12:00 UT). This improves the simple correlation of VLF wave intensity with flux, although the VLF effect in an overall multiple regression is still much less than that of other factors. When analyses are performed separately for season and interplanetary magnetic field (IMF) Bz orientation, VLF outweighs the influence of other factors only during winter months when IMF Bz is in an average northward orientation.
-
spatial structure and temporal evolution of energetic particle injections in the inner magnetosphere during the 14 july 2013 substorm event
Journal of Geophysical Research, 2015Co-Authors: M Gkioulidou, G D Reeves, D L Turner, A Y Ukhorskiy, S Ohtani, D G Mitchell, J W Gjerloev, M Nose, Kiyokazu Koga, J V RodriguezAbstract:Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside Geosynchronous Orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm (Dst ~ −40 nT) on 14 July 2013. Van Allen Probe B, inside Geosynchronous Orbit, observed two energetic proton injections within 10 min, with different dipolarization signatures and duration. The first one is a dispersionless, short-timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer-timescale injection pulse accompanied by a gradual dipolarization signature. We combined ground magnetometer data from various stations and in situ particle and magnetic field data from multiple satellites in the inner magnetosphere and near-Earth plasma sheet to determine the spatial extent of these injections, their temporal evolution, and their effects in the inner magnetosphere. Our results indicate that there are different spatial and temporal scales at which injections can occur in the inner magnetosphere and depict the necessity of multipoint observations of both particle and magnetic field data in order to determine these scales.
-
behavior of mev electrons at Geosynchronous Orbit during last two solar cycles
Journal of Geophysical Research, 2011Co-Authors: M Temerin, D N Baker, G D ReevesAbstract:[1] A comparison of MeV electron measurements at Geosynchronous Orbit, GEO, with solar wind shows that the MeV electron prediction model developed for GEO using data from the declining phase of solar cycle 22 (1995–1996) works well for the declining phase of solar cycle 23 (2006–2008), indicating that the MeV electron flux has a predictable and systematic response to the solar wind. The same comparison for solar maximum (2000–2003) shows that the model works less well partly because it does not match the high flux cutoff seen in the data and partly because it does not reproduce the sudden drops in flux that occur when the magnetopause is close to GEO. The model also reproduces the nonlinear correlation of the solar wind speed with the log of the MeV electron flux seen at GEO. An examination of 15 yr of solar wind and the MeV electron data shows that geomagnetic activity driven by a southward orientation of the interplanetary magnetic field, IMF, is a necessary condition for MeV electron enhancements at GEO and that high-speed solar wind are not necessary. The reason that high-speed solar wind is almost always associated with the enhancement of MeV electrons is mainly because high-speed solar wind almost always has some southward components of the IMF.
Joseph E Borovsky - One of the best experts on this subject based on the ideXlab platform.
-
an improved empirical model of electron and ion fluxes at Geosynchronous Orbit based on upstream solar wind conditions
Social Work, 2016Co-Authors: M F Thomsen, Joseph E Borovsky, M H Denton, M G Henderson, V K Jordanova, J R Woodroffe, D P Hartley, D PitchfordAbstract:In this study, a new empirical model of the electron fluxes and ion fluxes at Geosynchronous Orbit (GEO) is introduced, based on observations by Los Alamos National Laboratory (LANL) satellites. The model provides flux predictions in the energy range ~1 eV to ~40 keV, as a function of local time, energy, and the strength of the solar wind electric field (the negative product of the solar wind speed and the z component of the magnetic field). Given appropriate upstream solar wind measurements, the model provides a forecast of the fluxes at GEO with a ~1 h lead time. Model predictions are tested against in-sample observations from LANL satellites and also against out-of-sample observations from the Compact Environmental Anomaly Sensor II detector on the AMC-12 satellite. The model does not reproduce all structure seen in the observations. However, for the intervals studied here (quiet and storm times) the normalized root-mean-square deviation < ~0.3. It is intended that the model will improve forecasting of the spacecraft environment at GEO and also provide improved boundary/input conditions for physical models of the magnetosphere.
-
entropy mapping of the outer electron radiation belt between the magnetotail and Geosynchronous Orbit
Journal of Geophysical Research, 2011Co-Authors: Joseph E Borovsky, T E CaytonAbstract:[1] The specific entropy (entropy density) S is examined for the outer electron radiation belt at Geosynchronous Orbit and for the energetic electron population in the Earth's magnetotail. The outer electron radiation belt is measured with the SOPA detectors on board six Geosynchronous satellites and the energetic electrons of the magnetotail are measured with instrumentation on board 12 Global Positioning Satellites (GPS) with a magnetic field model used to map the GPS Orbit to the magnetotail. Density n and temperature T values are determined from relativistic Maxwellian fits to the electron measurements, enabling the specific entropy S to be calculated. For low temperatures the nonrelativstic specific entropy is S = T/n2/3; for a relativistic Maxwellian distribution a relativistically correct expression for S = S(T,n) is derived and used. The outer electron radiation belt at Geosynchronous Orbit local midnight (n ∼ 3 × 10−4 cm−3 and T ∼ 140 keV) and the energetic-electron population in the magnetotail (n ∼ 1 × 10−4 cm−3 and T ∼ 50 keV) statistically have the same specific entropy. Hence the two populations are probably the same. This implies adiabatic transport (1) from the magnetotail to the dipole (where the magnetotail electrons are the source of the outer electron radiation belt) or (2) from the dipole to the magnetotail (where the magnetotail electrons are leakage from the radiation belt).
-
on the heating of the outer radiation belt to produce high fluxes of relativistic electrons measured heating rates at Geosynchronous Orbit for high speed stream driven storms
Journal of Geophysical Research, 2010Co-Authors: Joseph E Borovsky, M H DentonAbstract:[1] The heating rate of the outer electron radiation belt at Geosynchronous Orbit is determined for the interval from 36 to 72 h after the onset of high-speed stream-driven storms. Multisatellite measurements of the radiation belt temperature are used for 93 high-speed stream-driven storms. During the storms, the outer electron radiation belt temperature changes from ∼120 keV to ∼190 keV. The average heating rate of 32 keV d−1 is obtained. The heating rate during the storms is found to be positively correlated with the solar wind velocity and with the Kp index of geomagnetic activity and to be negatively correlated with the solar wind number density. When the solar wind velocity is held fixed, the correlation of the heating rate with Kp vanishes. Expressions for the change in the heating rate as function of the solar wind speed, the solar wind density, and the Kp index are fit to the data. The heating rate is uncorrelated with the amplitude of magnetic field fluctuations in the magnetosphere. Correlations between the heating rate and the level of velocity, density, and magnetic field fluctuations in the magnetosphere and in the solar wind are weaker than the correlations of the heating rate with the solar wind velocity and density. The heating rates correspond to a kinetic energy density change of 3.6 × 10−11 erg cm−3 d−1 at Geosynchronous Orbit, to a specific entropy change of 4.1 × 106 eV cm2 d−1 at Geosynchronous Orbit, and to a total heating rate of the Geosynchronous Orbit region of 5.3 × 106 Watts.
-
superposed epoch analysis of high speed stream effects at Geosynchronous Orbit hot plasma cold plasma and the solar wind
Journal of Geophysical Research, 2008Co-Authors: M H Denton, Joseph E BorovskyAbstract:[1] Superposed epoch analyses of magnetospheric plasma analyzer (MPA) data from Los Alamos National Laboratory (LANL) satellites are performed to reveal the density, temperature and flow velocity behavior of the hot ion plasma (0.1–45 keV), the hot electron plasma (0.03–45 keV) and the cold ion plasma (1–100 eV) at Geosynchronous Orbit following the arrival of high speed solar wind streams at the dayside magnetopause. The analyses reveal three striking features. (1) The arrival of a high density solar wind plasma at the leading edge of a high speed solar wind stream induces a sharp enhancement in magnetospheric convection which leads to the delivery of a hot, dense “plug” of fresh plasma sheet ions and electrons to the inner magnetosphere. On average, this superdense plasma is observed at Geosynchronous Orbit for ∼20 h following convection onset. There follows an extended period when exceptionally hot plasma sheet ions and electrons of more usual density are continually convected to the inner magnetosphere - a environment that persists at Geosynchronous Orbit while the high speed stream prevails. (2) Flow velocities and convection speeds of eroded cold plasma moving toward the dayside magnetopause are calculated from MPA statistical analyses. Average convection speeds of 8–12 km s−1 are typical in plume material moving sunwards following the arrival of high speed solar wind streams at the magnetopause. (3) The density of plume material convecting to the dayside magnetopause during high speed streams which follow very calm periods (Kp ∼ 0) is around double that during high speed streams following periods when higher levels of convection persist (Kp ∼ 2).
J B Blake - One of the best experts on this subject based on the ideXlab platform.
-
multipoint observations of energetic particle injections and substorm activity during a conjunction between magnetospheric multiscale mms and van allen probes
Journal of Geophysical Research, 2017Co-Authors: D L Turner, S G Claudepierre, J B Blake, D N Baker, J. H. Clemmons, J F Fennell, A N Jaynes, T W Leonard, I J Cohen, M GkioulidouAbstract:This study examines multipoint observations during a conjunction between Magnetospheric Multiscale (MMS) and Van Allen Probes on 7 April 2016 in which a series of energetic particle injections occurred. With complementary data from Time History of Events and Macroscale Interactions during Substorms, Geotail, and Los Alamos National Laboratory spacecraft in Geosynchronous Orbit (16 spacecraft in total), we develop new insights on the nature of energetic particle injections associated with substorm activity. Despite this case involving only weak substorm activity (maximum AE <300 nT) during quiet geomagnetic conditions in steady, below-average solar wind, a complex series of at least six different electron injections was observed throughout the system. Intriguingly, only one corresponding ion injection was clearly observed. All ion and electron injections were observed at <600 keV only. MMS reveals detailed substructure within the largest electron injection. A relationship between injected electrons with energy <60 keV and enhanced whistler mode chorus wave activity is also established from Van Allen Probes and MMS. Drift mapping using a simplified magnetic field model provides estimates of the dispersionless injection boundary locations as a function of universal time, magnetic local time, and L shell. The analysis reveals that at least five electron injections, which were localized in magnetic local time, preceded a larger injection of both electrons and ions across nearly the entire nightside of the magnetosphere near Geosynchronous Orbit. The larger ion and electron injection did not penetrate to L < 6.6, but several of the smaller electron injections penetrated to L < 6.6. Due to the discrepancy between the number, penetration depth, and complexity of electron versus ion injections, this event presents challenges to the current conceptual models of energetic particle injections.
-
van allen probes themis goes and cluster observations of emic waves ulf pulsations and an electron flux dropout
Journal of Geophysical Research, 2016Co-Authors: K Sigsbee, C A Kletzing, C W Smith, R J Macdowall, H E Spence, G D Reeves, J B Blake, D N Baker, J C Green, H. J. SingerAbstract:We examined an electron flux dropout during the 12–14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS)-A (P5), Cluster 2, and Geostationary Operational Environmental Satellites (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at Geosynchronous Orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 h from 12 to 14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12–13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ electromagnetic ion cyclotron (EMIC) waves from just inside Geosynchronous Orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13–14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst <–100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finallymore » returned to near prestorm values, possibly in response to strong ultralow frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior.« less
-
the relativistic electron response at Geosynchronous Orbit during the january 1997 magnetic storm
Journal of Geophysical Research, 1998Co-Authors: G D Reeves, H. J. Singer, R H W Friedel, D N Baker, R D Belian, M M Meier, M G Henderson, T G Onsager, J B BlakeAbstract:The first geomagnetic storm of 1997 began on January 10. It is of particular interest because it was exceptionally well observed by the full complement of International Solar Terrestrial Physics (ISTP) satellites and because of its possible association with the catastrophic failure of the Telstar 401 telecommunications satellite. Here we report on the energetic electron environment observed by five Geosynchronous satellites. In part one of this paper we examine the magnetospheric response to the magnetic cloud. The interval of southward IMF drove strong substorm activity while the interval of northward IMF and high solar wind density strongly compressed the magnetosphere. At energies above a few hundred keV, two distinct electron enhancements were observed at Geosynchronous Orbit. The first enhancement began and ended suddenly, lasted for approximately 1 day, and is associated with the strong compression of the magnetosphere. The second enhancement showed a more characteristic time delay, peaking on January 15. Both enhancements may be due to transport of electrons from the same initial acceleration event at a location inside Geosynchronous Orbit but the first enhancement was due to a temporary, quasi-adiabatic transport associated with the compression of the magnetosphere while the second enhancement was due to slower diffusive processes. In the second part of the paper we compare the relativistic electron fluxes measured simultaneously at different local times. We find that the >2-MeV electron fluxes increased first at noon followed by dusk and then dawn and that there can be difference of two orders of magnitude in the fluxes observed at different local times. Finally, we discuss the development of data-driven models of the relativistic electron belts for space weather applications. By interpolating fluxes between satellites we produced a model that gives the >2-MeV electron fluxes at all local times as a function of universal time. In a first application of this model we show that, at least in this case, magnetopause shadowing does not contribute noticeably to relativistic electron dropouts.
-
radiation belt electron observations following the january 1997 magnetic cloud event
Geophysical Research Letters, 1998Co-Authors: R S Selesnick, J B BlakeAbstract:Relativistic electrons in the outer radiation belt associated with the January 1997 magnetic cloud event were observed by the HIST instrument on POLAR at kinetic energies from 0.7 to 7 MeV and L shells from 3 to 9. The electron enhancement occurred on a time scale of hours or less throughout the outer radiation belt, except for a more gradual rise in the higher energy electrons at the lower L values indicative of local acceleration and inward radial diffusion. At the higher L values, variations on a time scale of several days following the initial injection on January 10 are consistent with data from Geosynchronous Orbit and may be an adiabatic response.