Consider a typical configuration of the sampled-data control system. It consists of the plant to ... more Consider a typical configuration of the sampled-data control system. It consists of the plant to be controlled, a sampler, a discrete-time controller and a zero-order hold. Disturbance can be seen as an integral part of the plant so that the plant is characterized by the control path responsible for control signal influence on the output and the disturbance. The system output is usually sensed by sensors whose output signal can be corrupted by noise. Sometimes analog filters are put between the analog sensor output signal and sampler. In the control literature
Multipoint, high time resolution galactic cosmic ray observations associated with two interplanet... more Multipoint, high time resolution galactic cosmic ray observations associated with two interplanetary coronal mass ejections A. P. Jordan
This paper briefly reviews a number of fundamental measurements that need to be made in order to ... more This paper briefly reviews a number of fundamental measurements that need to be made in order to characterize turbulence in space plasmas such as the solar wind. It has long been known that many of these quantities require simultaneous multipoint measurements to attain a proper characterization that would reveal the fundamental physics of plasma turbulence. The solar wind is an ideal plasma for such an investigation, and it now appears to be technologically feasible to carry out such an investigation, following the pioneering Cluster and MMS missions. Quantities that need to be measured using multipoint measurements include the two-point, two-time second correlation function of velocity, magnetic field and density, and higher order statistical objects such as third and fourth order structure functions. Some details of these requirements are given here, with a eye towards achieving closure on fundamental questions regarding the cascade rate, spectral anisotropy, characteristic cohere...
Essential information regarding the magnetosphere's dynamic evolution and mapping resides in ... more Essential information regarding the magnetosphere's dynamic evolution and mapping resides in the coupling between global and local processes. This information, pertaining to the instantaneous wavenumber spectrum of the magnetospheric system remains today virtually untapped, mostly due to the enormity of the system's volume and the scarcity of fortuitous spatial conjunctions from previous platforms. The Constellation mission aspires to deploy a series of distributed observational platforms with varying degrees of sophisti cation, with the goal to understand the interchange of information and energy throughout the magnetospheric system. This paper summarizes proposed approaches and their scientific and technical justification. A phased deployment is proposed, whereby each platform will contribute significantly to the Constellation goal but building on its predecessors ensures an increasingly more comprehensive sampling of the medium. Prioritization of science goals, definition...
We present a machine-learning-based model of relativistic electron fluxes >1.8 MeV using a neu... more We present a machine-learning-based model of relativistic electron fluxes >1.8 MeV using a neural network approach in the Earth’s outer radiation belt. The Outer RadIation belt Electron Neural net model for Relativistic electrons (ORIENT-R) uses only solar wind conditions and geomagnetic indices as input. For the first time, we show that the state of the outer radiation belt can be determined using only solar wind conditions and geomagnetic indices, without any initial and boundary conditions. The most important features for determining outer radiation belt dynamics are found to be AL, solar wind flow speed and density, and SYM-H indices. ORIENTR reproduces out-of-sample relativistic electron fluxes with a correlation coefficient of 0.95 and an uncertainty factor of ~2. ORIENT-R reproduces radiation belt dynamics during an out-ofsample geomagnetic storm with good agreement to the observations. In addition, ORIENT-R was run for a completely out-of-sample period between March 2018 ...
The dipole configuration of the Earth's magnetic field allows for the trapping of highly ener... more The dipole configuration of the Earth's magnetic field allows for the trapping of highly energetic particles, which form the radiation belts. Although significant advances have been made in understanding the acceleration mechanisms in the radiation belts, the loss processes remain poorly understood. Unique observations on 17 January 2013 provide detailed information throughout the belts on the energy spectrum and pitch angle (angle between the velocity of a particle and the magnetic field) distribution of electrons up to ultra-relativistic energies. Here we show that although relativistic electrons are enhanced, ultra-relativistic electrons become depleted and distributions of particles show very clear telltale signatures of electromagnetic ion cyclotron wave-induced loss. Comparisons between observations and modelling of the evolution of the electron flux and pitch angle show that electromagnetic ion cyclotron waves provide the dominant loss mechanism at ultra-relativistic ener...
High-energy particles such as galactic cosmic rays (GCRs) and solar energetic particles (SEPs) ha... more High-energy particles such as galactic cosmic rays (GCRs) and solar energetic particles (SEPs) have sufficient kinetic energy to produce undesirable biological effects in astronauts as well as environmental effects on spacecraft electronic systems. In low Earth orbit, such radiation effects are minimized owing to the strong geomagnetic cutoff from Earth's internal magnetic field. However, the risks increase at higher altitudes
In this work we present analyses of events in which ULF wave activity was observed following the ... more In this work we present analyses of events in which ULF wave activity was observed following the impact of an interplanetary shock. The transmission of compressional energy from the impact of such shocks on the magnetosphere has been postulated as a source for global cavity mode oscillations. We show that oscillations inside the magnetosphere following the shock passage are well correlated with oscillations of the solar wind dynamic pressure, a result unexpected from the cavity mode model. Rather than providing a broadband source of energy to the magnetospheric cavity, we suggest that the magnetospheric pulsations are directly driven by the dynamic pressure variations.
Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric field... more Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeV electron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L ∼5.5, Van Allen Probes (Radiation Belt Storm Probes)-A observed a large dipolarization electric field (50 mV/m) over ∼40 s and a dispersionless injection of electrons up to ∼3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons.
Journal of Geophysical Research: Space Physics, 2015
During 18 February to 2 March 2014, the Van Allen Probes encountered multiple geomagnetic storms ... more During 18 February to 2 March 2014, the Van Allen Probes encountered multiple geomagnetic storms and simultaneously observed intensified chorus and hiss waves. During this period, there were substantial enhancements in fluxes of energetic (53.8-108.3 keV) and relativistic (2-3.6 MeV) electrons. Chorus waves were excited at locations L = 4-6.2 after the fluxes of energetic were greatly enhanced, with a lower frequency band and wave amplitudes ∼20-100 pT. Strong hiss waves occurred primarily in the main phases or below the location L = 4 in the recovery phases. Relativistic electron fluxes decreased in the main phases due to the adiabatic (e.g., the magnetopause shadowing) or nonadiabatic (hiss-induced scattering) processes. In the recovery phases, relativistic electron fluxes either increased in the presence of enhanced chorus or remained unchanged in the absence of strong chorus or hiss. The observed relativistic electron phase space density peaked around L * = 4.5, characteristic of local acceleration. This multiple-storm period reveals a typical picture that chorus waves are excited by the energetic electrons at first and then produce efficient acceleration of relativistic electrons. This further demonstrates that the interplay between both competing mechanisms of chorus-driven acceleration and hiss-driven scattering often occurs in the outer radiation belts.
We present Van Allen Probe observations of electrons in the inner radiation zone. The measurement... more We present Van Allen Probe observations of electrons in the inner radiation zone. The measurements were made by the Energetic Particle, Composition, and Thermal Plasma/Magnetic Electron Ion Spectrometer (MagEIS) sensors that were designed to measure electrons with the ability to remove unwanted signals from penetrating protons, providing clean measurements. No electrons >900 keV were observed with equatorial fluxes above background (i.e., >0.1 el/(cm 2 s sr keV)) in the inner zone. The observed fluxes are compared to the AE9 model and CRRES observations. Electron fluxes <200 keV exceeded the AE9 model 50% fluxes and were lower than the higher-energy model fluxes. Phase space density radial profiles for 1.3 ≤ L* < 2.5 had mostly positive gradients except near L*~2.1, where the profiles for μ = 20-30 MeV/G were flat or slightly peaked. The major result is that MagEIS data do not show the presence of significant fluxes of MeV electrons in the inner zone while current radiation belt models and previous publications do. FENNELL ET AL.
2013 US National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM), 2013
Energetic electron data from low-altitude Earth-orbiting spacecraft show both a long historical r... more Energetic electron data from low-altitude Earth-orbiting spacecraft show both a long historical record of the Van Allen radiation belts and the specific effects of powerful storms such as the 2003 Halloween storms. The fluxes of 2-6 MeV electrons measured by the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) from July 1992 to the current time are presented in this talk. Data demonstrate intense electron acceleration events (associated with high-speed solar wind), for example, in 1993-95 for 3 <; L <; 6. During sunspot minimum (1996), there were significant electron events only briefly around the spring and autumn equinoxes. The SAMPEX electron data for 2003 and throughout 2004 and 2005 show the shifted position of the outer Van Allen zone and the filling of the slot region (L<; 3). A persistent new belt of electrons was produced in the wake of the Halloween storms and this was clearly seen for L <; 2 for several years. We note that SAMPEX data demonstrate that in 2008 and 2009, the radiation belts virtually disappeared due to very weak solar wind driving conditions associated with the recent profound solar activity minimum period. Building on this historical record, we describe the new, exciting results from the Relativistic Electron-Proton Telescope (REPT) instrument that were launched successfully onboard the Radiation Belt Storm Probes mission on 30 August 2012. Key areas of scientific progress using REPT will be addressed. Excellent new data from the twin REPT instruments are available from the initial turn-on (Launch+3 days) of the instruments to the present. Inner and outer zone electron spectra have been compared with model expectations.
Consider a typical configuration of the sampled-data control system. It consists of the plant to ... more Consider a typical configuration of the sampled-data control system. It consists of the plant to be controlled, a sampler, a discrete-time controller and a zero-order hold. Disturbance can be seen as an integral part of the plant so that the plant is characterized by the control path responsible for control signal influence on the output and the disturbance. The system output is usually sensed by sensors whose output signal can be corrupted by noise. Sometimes analog filters are put between the analog sensor output signal and sampler. In the control literature
Multipoint, high time resolution galactic cosmic ray observations associated with two interplanet... more Multipoint, high time resolution galactic cosmic ray observations associated with two interplanetary coronal mass ejections A. P. Jordan
This paper briefly reviews a number of fundamental measurements that need to be made in order to ... more This paper briefly reviews a number of fundamental measurements that need to be made in order to characterize turbulence in space plasmas such as the solar wind. It has long been known that many of these quantities require simultaneous multipoint measurements to attain a proper characterization that would reveal the fundamental physics of plasma turbulence. The solar wind is an ideal plasma for such an investigation, and it now appears to be technologically feasible to carry out such an investigation, following the pioneering Cluster and MMS missions. Quantities that need to be measured using multipoint measurements include the two-point, two-time second correlation function of velocity, magnetic field and density, and higher order statistical objects such as third and fourth order structure functions. Some details of these requirements are given here, with a eye towards achieving closure on fundamental questions regarding the cascade rate, spectral anisotropy, characteristic cohere...
Essential information regarding the magnetosphere's dynamic evolution and mapping resides in ... more Essential information regarding the magnetosphere's dynamic evolution and mapping resides in the coupling between global and local processes. This information, pertaining to the instantaneous wavenumber spectrum of the magnetospheric system remains today virtually untapped, mostly due to the enormity of the system's volume and the scarcity of fortuitous spatial conjunctions from previous platforms. The Constellation mission aspires to deploy a series of distributed observational platforms with varying degrees of sophisti cation, with the goal to understand the interchange of information and energy throughout the magnetospheric system. This paper summarizes proposed approaches and their scientific and technical justification. A phased deployment is proposed, whereby each platform will contribute significantly to the Constellation goal but building on its predecessors ensures an increasingly more comprehensive sampling of the medium. Prioritization of science goals, definition...
We present a machine-learning-based model of relativistic electron fluxes >1.8 MeV using a neu... more We present a machine-learning-based model of relativistic electron fluxes >1.8 MeV using a neural network approach in the Earth’s outer radiation belt. The Outer RadIation belt Electron Neural net model for Relativistic electrons (ORIENT-R) uses only solar wind conditions and geomagnetic indices as input. For the first time, we show that the state of the outer radiation belt can be determined using only solar wind conditions and geomagnetic indices, without any initial and boundary conditions. The most important features for determining outer radiation belt dynamics are found to be AL, solar wind flow speed and density, and SYM-H indices. ORIENTR reproduces out-of-sample relativistic electron fluxes with a correlation coefficient of 0.95 and an uncertainty factor of ~2. ORIENT-R reproduces radiation belt dynamics during an out-ofsample geomagnetic storm with good agreement to the observations. In addition, ORIENT-R was run for a completely out-of-sample period between March 2018 ...
The dipole configuration of the Earth's magnetic field allows for the trapping of highly ener... more The dipole configuration of the Earth's magnetic field allows for the trapping of highly energetic particles, which form the radiation belts. Although significant advances have been made in understanding the acceleration mechanisms in the radiation belts, the loss processes remain poorly understood. Unique observations on 17 January 2013 provide detailed information throughout the belts on the energy spectrum and pitch angle (angle between the velocity of a particle and the magnetic field) distribution of electrons up to ultra-relativistic energies. Here we show that although relativistic electrons are enhanced, ultra-relativistic electrons become depleted and distributions of particles show very clear telltale signatures of electromagnetic ion cyclotron wave-induced loss. Comparisons between observations and modelling of the evolution of the electron flux and pitch angle show that electromagnetic ion cyclotron waves provide the dominant loss mechanism at ultra-relativistic ener...
High-energy particles such as galactic cosmic rays (GCRs) and solar energetic particles (SEPs) ha... more High-energy particles such as galactic cosmic rays (GCRs) and solar energetic particles (SEPs) have sufficient kinetic energy to produce undesirable biological effects in astronauts as well as environmental effects on spacecraft electronic systems. In low Earth orbit, such radiation effects are minimized owing to the strong geomagnetic cutoff from Earth's internal magnetic field. However, the risks increase at higher altitudes
In this work we present analyses of events in which ULF wave activity was observed following the ... more In this work we present analyses of events in which ULF wave activity was observed following the impact of an interplanetary shock. The transmission of compressional energy from the impact of such shocks on the magnetosphere has been postulated as a source for global cavity mode oscillations. We show that oscillations inside the magnetosphere following the shock passage are well correlated with oscillations of the solar wind dynamic pressure, a result unexpected from the cavity mode model. Rather than providing a broadband source of energy to the magnetospheric cavity, we suggest that the magnetospheric pulsations are directly driven by the dynamic pressure variations.
Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric field... more Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeV electron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L ∼5.5, Van Allen Probes (Radiation Belt Storm Probes)-A observed a large dipolarization electric field (50 mV/m) over ∼40 s and a dispersionless injection of electrons up to ∼3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons.
Journal of Geophysical Research: Space Physics, 2015
During 18 February to 2 March 2014, the Van Allen Probes encountered multiple geomagnetic storms ... more During 18 February to 2 March 2014, the Van Allen Probes encountered multiple geomagnetic storms and simultaneously observed intensified chorus and hiss waves. During this period, there were substantial enhancements in fluxes of energetic (53.8-108.3 keV) and relativistic (2-3.6 MeV) electrons. Chorus waves were excited at locations L = 4-6.2 after the fluxes of energetic were greatly enhanced, with a lower frequency band and wave amplitudes ∼20-100 pT. Strong hiss waves occurred primarily in the main phases or below the location L = 4 in the recovery phases. Relativistic electron fluxes decreased in the main phases due to the adiabatic (e.g., the magnetopause shadowing) or nonadiabatic (hiss-induced scattering) processes. In the recovery phases, relativistic electron fluxes either increased in the presence of enhanced chorus or remained unchanged in the absence of strong chorus or hiss. The observed relativistic electron phase space density peaked around L * = 4.5, characteristic of local acceleration. This multiple-storm period reveals a typical picture that chorus waves are excited by the energetic electrons at first and then produce efficient acceleration of relativistic electrons. This further demonstrates that the interplay between both competing mechanisms of chorus-driven acceleration and hiss-driven scattering often occurs in the outer radiation belts.
We present Van Allen Probe observations of electrons in the inner radiation zone. The measurement... more We present Van Allen Probe observations of electrons in the inner radiation zone. The measurements were made by the Energetic Particle, Composition, and Thermal Plasma/Magnetic Electron Ion Spectrometer (MagEIS) sensors that were designed to measure electrons with the ability to remove unwanted signals from penetrating protons, providing clean measurements. No electrons >900 keV were observed with equatorial fluxes above background (i.e., >0.1 el/(cm 2 s sr keV)) in the inner zone. The observed fluxes are compared to the AE9 model and CRRES observations. Electron fluxes <200 keV exceeded the AE9 model 50% fluxes and were lower than the higher-energy model fluxes. Phase space density radial profiles for 1.3 ≤ L* < 2.5 had mostly positive gradients except near L*~2.1, where the profiles for μ = 20-30 MeV/G were flat or slightly peaked. The major result is that MagEIS data do not show the presence of significant fluxes of MeV electrons in the inner zone while current radiation belt models and previous publications do. FENNELL ET AL.
2013 US National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM), 2013
Energetic electron data from low-altitude Earth-orbiting spacecraft show both a long historical r... more Energetic electron data from low-altitude Earth-orbiting spacecraft show both a long historical record of the Van Allen radiation belts and the specific effects of powerful storms such as the 2003 Halloween storms. The fluxes of 2-6 MeV electrons measured by the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) from July 1992 to the current time are presented in this talk. Data demonstrate intense electron acceleration events (associated with high-speed solar wind), for example, in 1993-95 for 3 <; L <; 6. During sunspot minimum (1996), there were significant electron events only briefly around the spring and autumn equinoxes. The SAMPEX electron data for 2003 and throughout 2004 and 2005 show the shifted position of the outer Van Allen zone and the filling of the slot region (L<; 3). A persistent new belt of electrons was produced in the wake of the Halloween storms and this was clearly seen for L <; 2 for several years. We note that SAMPEX data demonstrate that in 2008 and 2009, the radiation belts virtually disappeared due to very weak solar wind driving conditions associated with the recent profound solar activity minimum period. Building on this historical record, we describe the new, exciting results from the Relativistic Electron-Proton Telescope (REPT) instrument that were launched successfully onboard the Radiation Belt Storm Probes mission on 30 August 2012. Key areas of scientific progress using REPT will be addressed. Excellent new data from the twin REPT instruments are available from the initial turn-on (Launch+3 days) of the instruments to the present. Inner and outer zone electron spectra have been compared with model expectations.
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Papers by Harlan Spence