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M H Denton - One of the best experts on this subject based on the ideXlab platform.
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the proton and Electron Radiation belts at geosynchronous orbit statistics and behavior during high speed stream driven storms
2016Co-Authors: T E Cayton, Joseph E Borovsky, 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.
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case studies of the impact of high speed solar wind streams on the Electron Radiation belt at geosynchronous orbit flux magnetic field and phase space density
2013Co-Authors: Dave Hartley, M H Denton, J C Green, T G Onsager, J V Rodriguez, H J SingerAbstract:Investigation of Electron Radiation belt dropouts has revealed the importance of a number of loss processes, yet there remains a lack of quantitative detail as to how these processes wax and wane between events. The overarching aim of this study is to address the issue of Electron Radiation belt dropouts. This is achieved using in situ observations at geostationary orbit from GOES-13 (pitch-angle-resolved Electron data and magnetic field measurements) to examine the outer Electron Radiation belt during three high-speed stream-driven storms. Analysis and interpretation are aided by calculation of the phase space density (PSD) as a function of the three adiabatic invariants. Our results confirm the importance of outwards adiabatic transport as a mechanism for causing Electron dropouts at GEO, however study of the pitch-angle distributions indicates that other loss mechanisms are also likely to be occurring during these HSS-driven storms. Two of the studied events exhibit similar evolutionary structure in their pitch-angle distributions, (i) highly peaked distributions immediately prior to the dropout (ii) sharp transitions between peaked and isotropic and then subsequent butterfly distributions, and (iii) isotropic distributions at minimum flux shortly afterwards (dusk). We also address the difficulty in interpreting PSD calculations by comparing the T96 model magnetic field with that measured by GOES-13. Our results are intended as a first step in quantifying the timeline of events that occur in the Radiation belts following the arrival of a HSS - particularly timely given the increase in HSS-occurrence expected in the declining phase of the current solar cycle.
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evolution of the magnetotail energetic Electron population during high speed stream driven storms evidence for the leakage of the outer Electron Radiation belt into the earth s magnetotail
2011Co-Authors: Joseph E Borovsky, M H DentonAbstract:For 15 high-speed-stream-driven geomagnetic activations (weak storms) in 2006-2007, the temporal behaviors of the outer Electron Radiation belt at geosynchronous orbit and the energetic-Electron population of the magnetotail are compared via superposed-epoch averaging of data. The magnetotail measurements are obtained by using GPS-orbit measurements that magnetically map out into the magnetotail. Four temporal phases of high-speed-stream-driven storms are studied: (1) the pre-storm density decay of the Electron-Radiation belt, (2) the Electron-Radiation-belt density dropout near the time of storm onset, (3) the rapid density recovery a few hours after dropout, and (4) the heating of the Electron Radiation belt during the high-speed-stream-driven geomagnetic activity. In all four phases the behaviors of the outer Electron Radiation belt and of the energetic-Electron population in the magnetotail are the same and simultaneous. The physical explanations for the behavior in phase 1 (decay), phase 2 (dropout), and phase 4 (heating) lie in the dipolar regions of the magnetosphere: hence for those three phases it is concluded that the temporal behavior of the energetic-Electron population in the magnetotail mimics the behavior of the outer Electron Radiation belt. Behavior attributable to physical processes in the dipole is seen in the magnetotail energetic-Electron population: this implies that the origin of the energetic-Electron population of the magnetotail is "leakage" or "outward evaporation" from the outer Electron Radiation belt in the dipolar magnetosphere.
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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
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.
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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
2010Co-Authors: Joseph E Borovsky, 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.
Joseph E Borovsky - One of the best experts on this subject based on the ideXlab platform.
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the contribution of compressional magnetic pumping to the energization of the earth s outer Electron Radiation belt during high speed stream driven storms
2017Co-Authors: Joseph E Borovsky, Richard B Horne, Nigel P. MeredithAbstract:Compressional magnetic pumping is an interaction between cyclic magnetic compressions and pitch-angle scattering with the scattering acting as a catalyst to allow the cyclic compressions to energize particles. Compressional magnetic pumping of the outer Electron Radiation belt at geosynchronous orbit in the dayside magnetosphere is analyzed by means of computer simulations, wherein solar-wind compressions of the dayside magnetosphere energize Electrons with Electron pitch-angle scattering by chorus waves and by EMIC. The magnetic pumping is found to produce a weak bulk heating of the Electron Radiation belt, and it also produces an energetic tail on the Electron energy distribution. The amount of energization depends on the robustness of the solar-wind compressions and on the amplitude of the chorus and/or EMIC waves. Chorus-catalyzed pumping is better at energizing medium-energy (50 - 200 keV) Electrons than it is at energizing higher energy Electrons; at high energies (500 keV - 2 MeV) EMIC-catalyzed pumping is a stronger energizer. The magnetic-pumping simulation results are compared with energy-diffusion calculations for chorus waves in the dayside magnetosphere; in general compressional magnetic pumping is found to be weaker at accelerating Electrons than is chorus-driven energy diffusion. In circumstances when solar-wind compressions are robust and when EMIC waves are present in the dayside magnetosphere without the presence of chorus, EMIC-catalyzed magnetic pumping could be the dominant energization mechanism in the dayside magnetosphere, but at such times loss-cone losses will be strong.
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the proton and Electron Radiation belts at geosynchronous orbit statistics and behavior during high speed stream driven storms
2016Co-Authors: T E Cayton, Joseph E Borovsky, 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.
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evolution of the magnetotail energetic Electron population during high speed stream driven storms evidence for the leakage of the outer Electron Radiation belt into the earth s magnetotail
2011Co-Authors: Joseph E Borovsky, M H DentonAbstract:For 15 high-speed-stream-driven geomagnetic activations (weak storms) in 2006-2007, the temporal behaviors of the outer Electron Radiation belt at geosynchronous orbit and the energetic-Electron population of the magnetotail are compared via superposed-epoch averaging of data. The magnetotail measurements are obtained by using GPS-orbit measurements that magnetically map out into the magnetotail. Four temporal phases of high-speed-stream-driven storms are studied: (1) the pre-storm density decay of the Electron-Radiation belt, (2) the Electron-Radiation-belt density dropout near the time of storm onset, (3) the rapid density recovery a few hours after dropout, and (4) the heating of the Electron Radiation belt during the high-speed-stream-driven geomagnetic activity. In all four phases the behaviors of the outer Electron Radiation belt and of the energetic-Electron population in the magnetotail are the same and simultaneous. The physical explanations for the behavior in phase 1 (decay), phase 2 (dropout), and phase 4 (heating) lie in the dipolar regions of the magnetosphere: hence for those three phases it is concluded that the temporal behavior of the energetic-Electron population in the magnetotail mimics the behavior of the outer Electron Radiation belt. Behavior attributable to physical processes in the dipole is seen in the magnetotail energetic-Electron population: this implies that the origin of the energetic-Electron population of the magnetotail is "leakage" or "outward evaporation" from the outer Electron Radiation belt in the dipolar magnetosphere.
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entropy mapping of the outer Electron Radiation belt between the magnetotail and geosynchronous orbit
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).
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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
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.
Yuri Shprits - One of the best experts on this subject based on the ideXlab platform.
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quantifying the effects of emic wave scattering and magnetopause shadowing in the outer Electron Radiation belt by means of data assimilation
2020Co-Authors: Sebastian Cervantes, Yuri Shprits, Nikita Aseev, Hayley J AllisonAbstract:In this study we investigate two distinct loss mechanisms responsible for the rapid dropouts of Radiation belt Electrons by assimilating data from Van Allen Probes A and B and Geostationary Operati...
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new hiss and chorus waves diffusion coefficient parameterizations from the van allen probes and their effect on long term relativistic Electron Radiation belt verb simulations
2019Co-Authors: Hui Zhu, Yuri Shprits, M Spasojevic, A DrozdovAbstract:Abstract New wave frequency and amplitude models for the nightside and dayside chorus waves are built based on measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument onboard the Van Allen Probes. The corresponding 3D diffusion coefficients are systematically obtained. Compared with previous commonly-used (typical) parameterizations, the new parameterizations result in differences in diffusion rates that depend on the energy and pitch angle. Furthermore, one-year 3D diffusive simulations are performed using the Versatile Electron Radiation Belt (VERB) code. Both typical and new wave parameterizations simulation results are in a good agreement with observations at 0.9 MeV. However, the new parameterizations for nightside chorus better reproduce the observed Electron fluxes. These parameterizations will be incorporated into future modeling efforts.
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formation of Electron Radiation belts at saturn by z mode wave acceleration
2018Co-Authors: E E Woodfield, Richard B Horne, Sarah A. Glauert, Yuri Shprits, J D Menietti, W S KurthAbstract:At Saturn Electrons are trapped in the planet’s magnetic field and accelerated to relativistic energies to form the Radiation belts, but how this dramatic increase in Electron energy occurs is still unknown. Until now the mechanism of radial diffusion has been assumed but we show here that in-situ acceleration through wave particle interactions, which initial studies dismissed as ineffectual at Saturn, is in fact a vital part of the energetic particle dynamics there. We present evidence from numerical simulations based on Cassini spacecraft data that a particular plasma wave, known as Z-mode, accelerates Electrons to MeV energies inside 4 RS (1 RS = 60,330 km) through a Doppler shifted cyclotron resonant interaction. Our results show that the Z-mode waves observed are not oblique as previously assumed and are much better accelerators than O-mode waves, resulting in an Electron energy spectrum that closely approaches observed values without any transport effects included. Radial diffusion is the only mechanism considered to accelerate trapped Electrons to relativistic energies in Saturn’s magnetic field, forming Radiation belts. Here the authors show another mechanism, Electron acceleration via Doppler shifted cyclotron resonant interaction with Z-mode waves, which can form Radiation belts inside the orbit of Enceladus.
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Formation of Electron Radiation belts at Saturn by Z-mode wave acceleration
2018Co-Authors: Emma Woodfield, Richard B Horne, Sarah A. Glauert, Yuri Shprits, J D Menietti, W S KurthAbstract:At Saturn Electrons are trapped in the planet's magnetic field and accelerated to relativistic energies to form the Radiation belts, but how this dramatic increase in Electron energy occurs is still unknown. Until now the mechanism of radial diffusion has been assumed but we show here that in-situ acceleration through wave particle interactions, which initial studies dismissed as ineffectual at Saturn, is in fact a vital part of the energetic particle dynamics there. We present evidence from numerical simulations based on Cassini spacecraft data that a particular plasma wave, known as Z-mode, accelerates Electrons to MeV energies inside 4 RS (1 RS = 60,330 km) through a Doppler shifted cyclotron resonant interaction. Our results show that the Z-mode waves observed are not oblique as previously assumed and are much better accelerators than O-mode waves, resulting in an Electron energy spectrum that closely approaches observed values without any transport effects included.
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dynamic responses of the earth s Radiation belts during periods of solar wind dynamic pressure pulse based on normalized superposed epoch analysis
2016Co-Authors: Zheng Xiang, Yuri Shprits, Chen Zhou, Zhengyu Zhao, Xianguo Zhang, Pingbing ZuoAbstract:Using the Electron flux measurements obtained from five satellites (GOES-15 and POES 15, 16, 18, and 19), we investigate the flux variations of Radiation belt Electrons during forty solar wind dynamic pressure pulses identified between September 2012 and December 2014. By utilizing the mean duration of the pressure pulses as the epoch timeline and stretching or compressing the time phases of individual events to normalize the duration by means of linear interpolation, we have performed normalized superposed epoch analysis to evaluate the dynamic responses of Radiation belt energetic Electrons corresponding to various groups of solar wind and magnetospheric conditions in association with solar wind dynamic pressure pulses. Our results indicate that by adopting the timeline normalization we can reproduce the typical response of the Electron Radiation belts to pressure pulses. Radiation belt Electron fluxes exhibit large depletions right after the Pdyn peak during the periods of northward IMF Bz and are more likely to occur during the Pdyn pulse under southward IMF Bz conditions. For the pulse events with large negative values of (Dst)min, Radiation belt Electrons respond in a manner similar to those with southward IMF Bz, and the corresponding post-pulse recovery can extend to L ~ 3 and exceed the pre-pulse flux levels. Triggered by the solar wind pressure enhancements, deeper earthward magnetopause erosion provides favorable conditions for the prompt Electron flux dropouts that extend down to L ~ 5, and the pressure pulses with longer duration tend to produce quicker and stronger Electron flux decay. In addition, the events with high Electron fluxes before the Pdyn pulse tend to experience more severe Electron flux dropouts during the course of the pulse, while the largest rate of Electron flux increase before and after the pulse occurs under the pre-conditioned low Electron fluxes. These new results help us understand how Electron fluxes respond to solar wind dynamic pressure pulses and how these responses depend on the solar wind and geomagnetic conditions and on the preconditions in the Electron Radiation belts.
T E Cayton - One of the best experts on this subject based on the ideXlab platform.
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the proton and Electron Radiation belts at geosynchronous orbit statistics and behavior during high speed stream driven storms
2016Co-Authors: T E Cayton, Joseph E Borovsky, 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.
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entropy mapping of the outer Electron Radiation belt between the magnetotail and geosynchronous orbit
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).
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dropouts of the outer Electron Radiation belt in response to solar wind stream interfaces global positioning system observations
2010Co-Authors: S K Morley, G D Reeves, R H W Friedel, E Spanswick, J T Steinberg, J Koller, T E Cayton, Evan NoveroskeAbstract:We present a statistical study of relativistic Electron counts in the Electron Radiation belt across a range of drift shells (L*>4) combining data from nine combined X-ray dosimeters (CXD) on the global positioning system (GPS) constellation. The response of the Electron counts as functions of time, energy and drift shell are examined statistically for 67 solar wind stream interfaces (SIs); two-dimensional superposed epoch analysis is performed with the CXD data. For these epochs we study the Radiation belt dropouts and concurrent variations in key geophysical parameters. At higher L* we observe a tendency for a gradual drop in the Electron counts over the day preceding the SI, consistent with outward diffusion and magnetopause shadowing. At all L*, dropouts occur with a median time scale of ≃7 h and median counts fall by 0.4–1.8 orders of magnitude. The central tendencies of Radiation belt dropout and recovery depend on both L* and energy. For ≃70 per cent of epochs Sym-H more than −30 nT, yet only three of 67 SIs did not have an associated dropout in the Electron data. Statistical maps of Electron precipitation suggest that chorus-driven relativistic Electron microbursts might be major contributors to Radiation belt losses under high-speed stream driving.
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a density temperature description of the outer Electron Radiation belt during geomagnetic storms
2010Co-Authors: M H Denton, Joseph E Borovsky, T E CaytonAbstract:Bi-Maxwellian fits are made to energetic-Electron flux measurements from seven satellites in geosynchronous orbit, yielding a number density (n) and temperature (T) description of the outer Electron Radiation belt. For 54.5 spacecraft years of measurements the median value of n is 3.7 × 10−4 cm−3, and the median value of T is 148 keV. General statistical properties of n, T, and the 1.1–1.5 MeV flux F are investigated, including local-time and solar-cycle dependencies. Using superposed-epoch analysis where the zero epoch is convection onset, the evolution of the outer Electron Radiation belt through high-speed-stream-driven storms is investigated. The number-density decay during the calm before the storm, relativistic-Electron dropouts and recoveries, and the heating of the outer Electron Radiation belt during storms are analyzed. Using four different “triggers” (sudden storm commencement (SSC), southward interplanetary magnetic field (IMF) portions of coronal mass ejection (CME) sheaths, southward-IMF portions of magnetic clouds, and minimum Dst) a selection of CME-driven storms are analyzed with superposed-epoch techniques. For CME-driven storms, only a very modest density decay prior to storm onset is found. In addition, the compression of the outer Electron Radiation belt at the time of SSC is analyzed, the number-density increase and temperature decrease during storm main phase are characterized, and the increase in density and temperature during storm recovery phase is determined. During the different phases of storms, changes in the flux are sometimes in response to changes in the temperature, sometimes to changes in the number density, and sometimes to changes in both. Differences are found between the density-temperature and flux descriptions, and it is concluded that more information is available using the density-temperature description.
Falk Roeder - One of the best experts on this subject based on the ideXlab platform.
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intraoperative Electron Radiation therapy combined with external beam Radiation therapy after gross total resection in extremity soft tissue sarcoma a european pooled analysis
2018Co-Authors: Falk Roeder, Antonino De Paoli, Ladan Salehebrahimi, Ingo Alldinger, G Bertola, G Boz, F Navarria, Miguel Cuervo, Matthias UhlAbstract:We report a pooled analysis evaluating the combination of gross complete limb-sparing surgery, intraoperative Electron Radiation therapy (IOERT), and external beam Radiation therapy (EBRT) in patients with extremity soft tissue sarcoma (STS). Individual data of 259 patients (median follow-up 63 months) with extremity STS from three European expert centers were pooled. Median age was 55 years and median tumor size was 8 cm. Eighty percent of patients presented with primary disease, mainly located in the lower limb (81%). Union for International Cancer Control 7th edition stage at presentation was as follows: stage I: 9%; stage II: 47%; stage III: 39%; stage IV: 5%. Most patients showed high-grade lesions (91%), predominantly liposarcoma (31%). Median IOERT dose was 12 Gy, preceeded (17%) or followed (83%) by EBRT, with a median dose of 45 Gy. Surgery resulted in R0 resections in 71% of patients and R1 resections in 29% of patients. The 5-year local control (LC) rate was 86%, and significant factors in univariate analysis were disease status and resection margin. Only margin remained significant in multivariate analysis. The 5-year distant control rate was 69%, and significant factors in univariate analysis were histology, grading, resection margin, and metastases prior to/at IOERT. Only grading and metastases remained significant in multivariate analysis. Actuarial 5-year rates of freedom from treatment failure and OS were 61% and 78%, respectively. Significant factors for OS were grading and metastases prior to/at IOERT (univariate, multivariate). Limb preservation and good functional outcome were achieved in 95% and 81% of patients. Our pooled analysis confirmed prior reports of encouraging LC and survival, with excellent rates of preserved limb function with this treatment approach. Resection margin remained the most important factor for LC, while grading and metastases prior to/at IOERT mainly predicted survival.
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intraoperative Electron Radiation therapy in retroperitoneal sarcoma
2018Co-Authors: Matthias Uhl, Falk Roeder, Jurgen Debus, Ladan Salehebrahimi, Ingo Alldinger, Simon Schimmack, Gunhild Mechtersheimer, Markus W BuchlerAbstract:Purpose To report our experience with surgery, intraoperative Radiation therapy (IORT), and external beam Radiation therapy (EBRT) in retroperitoneal soft-tissue sarcoma. Methods and Materials We conducted a retrospective evaluation of 156 patients (69 primary, 87 recurrent) treated with IORT since 1991. The dominant histology was dedifferentiated liposarcoma (49%); 89% of lesions were high grade. Median tumor size was 11 cm. Surgery resulted in gross complete resection in 92%, and 65% had microscopically positive margins. Median IORT dose was 15 Gy. A total of 114 patients (73%) received additional EBRT (preoperatively n=38, postoperatively n=76, median dose 45 Gy). Results Median follow-up was 38 months (49 months in survivors). The 3- and 5-year local control (LC) rates were 57% and 50%, respectively. On univariate analysis, LC was significantly associated with primary versus recurrent status, histology, grade, Union for International Cancer Control (UICC) stage, resection margin, and addition of EBRT. The 5-year LC was 71% in the primary situation and 79% after R0 resection. On multivariate analysis only disease status, grade, resection margin, and addition of EBRT remained statistically significant. The 3- and 5-year overall survival (OS) rates were 66% and 56%. On univariate analysis, OS was significantly associated with primary versus recurrent status, histology, grade, UICC stage, resection margin, and timing of EBRT. The 5-year OS was 63% in the primary situation and 68% after R0 resection. On multivariate analysis only disease status, grade, and resection margin remained independent prognostic factors. Perioperative mortality was 1%, and major complications occurred in 34% (mainly wound complications). Conclusions Treatment with surgery, IORT, and EBRT is feasible and resulted in good LC and OS, with acceptable morbidity in this unfavorable patient cohort. Incomplete resection and recurrent status resulted in clearly inferior outcomes. Reasonable efforts should be made during primary treatment to prevent the onset of a local recurrence.
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outcome of patients with local recurrent gynecologic malignancies after resection combined with intraoperative Electron Radiation therapy ioert
2016Co-Authors: Nathalie Arians, Robert Foerster, Joachim Rom, Matthias Uhl, Falk Roeder, Jurgen Debus, Katja LindelAbstract:Treatment of recurrent gynecologic cancer is a challenging issue. Aim of the study was to investigate clinical features and outcomes of patients with recurrent gynecologic malignancies who underwent resection including IOERT (intraoperative Electron Radiation therapy) with regard to clinical outcome and potential predictive factors or subgroups that benefit most from this radical treatment regime. A total of 36 patients with recurrent gynecologic malignancies (cervical (n = 18), endometrial (n = 12) or vulvar cancer (n = 6)) were retrospectively identified through hospital databases in accordance with institutional ethical policies. Patient characteristics and outcomes were assessed. Survival data was analyzed using the Kaplan-Meier-method and log-rank-test, categorical variables were analyzed with chi-square-method. For the entire cohort 1-/2-/5-year Overall Survival (OS) was 65.3 %/36.2 %/21.7 %. Patients with endometrial, cervical, and vulvar carcinoma had a 1-/2-/5-year OS of 83.3 %/62.5 %/50 %, 44.5 %/25.4 %/6.4 %, and 83.3 %/16.7 %/16.7 %, respectively. Patients with endometrial carcinoma showed a significantly better OS (p = 0.038). 1-/2-/5-year Local Progression-free Survival (LPFS) for the entire cohort was 44.1 %/28 %/21 % with 76.2 %/61 %/40.6 % for endometrial, 17.2 %/0 %/0 % for cervical, and 40 %/20 %/20 % for vulvar cancer, respectively. Patients with endometrial cancer showed a significantly (p = 0.017) and older patients a trend (p = 0.059) for a better LPFS. 1-/2-/5-year Distant Progression-free Survival (DPFS) for the entire cohort was 53.1 %/46.5 %/38.7 % with 74.1 %/74.1 %/74.1 % for endometrial, 36.7 %/36.7 %/0 % for cervical, and 60 %/30 %/30 % for vulvar cancer, respectively. There was a significantly better DPFS for older patients (p = 0.015) and a trend for a better DPFS for patients with endometrial carcinoma (p = 0.075). The radical procedure of resection combined with IOERT seems to be a valid curative treatment option for patients with recurrent endometrial carcinoma with 5-year survival rates of 50 %. For patients with cervical or vulvar cancer this treatment should be considered a rather palliative one and must be weighted carefully against other treatment options like chemotherapy, targeted therapies or new highly conformal radiotherapy techniques.
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intraoperative Electron Radiation therapy ioert in the management of locally recurrent rectal cancer
2012Co-Authors: Falk Roeder, Joerg Michael Goetz, Gregor Habl, Marc Bischof, Robert Krempien, Markus W Buechler, Frank W Hensley, Peter E HuberAbstract:Background To evaluate disease control, overall survival and prognostic factors in patients with locally recurrent rectal cancer after IOERT-containing multimodal therapy.