Los Alamos National Laboratory Satellites Research Articles

Removing Diurnal Signals and Longer Term Trends From Electron Flux and ULF Correlations: A Comparison of Spectral Subtraction, Simple Differencing, and ARIMAX Models

AbstractSimultaneously cycling space weather parameters may show high correlations even if there is no immediate relationship between them. We successfully remove diurnal cycles using spectral subtraction, and remove both diurnal and longer cycles (e.g., the 27 days solar cycle) with a difference transformation. Other methods of diurnal cycle removal (daily averaging, moving averages [MAs], and simpler spectral subtraction using regression) are less successful at removing cycles. We apply spectral subtraction (a finite impulse response equiripple bandstop filter) to hourly electron flux (Los Alamos National Laboratory satellite data) and a ground‐based ULF index to remove a 24 hr noise signal. This results in smoother time series appropriate for short‐term (approximately < 1 week) correlation and observational studies. However, spectral subtraction may not remove longer cycles such as the 27 days and 11 yr solar cycles. A differencing transformation (yt – yt−24) removes not only the 24 hr noise signal but also the 27 days solar cycle, autocorrelation, and longer trends. This results in a low correlation between electron flux and the ULF index over long periods of time (maximum of 0.1). Correlations of electron flux and the ULF index with solar wind velocity (differenced at yt – yt−1) are also lower than previously reported (≤0.1). An autoregressive, MA transfer function model (ARIMAX) shows that there are significant cumulative effects of solar wind velocity on ULF activity over long periods, but correlations of velocity and ULF waves with flux are only seen over shorter time spans of more homogeneous geomagnetic activity levels.

Worst‐Case Severe Environments for Surface Charging Observed at LANL Satellites as Dependent on Solar Wind and Geomagnetic Conditions

AbstractThe 400 worst‐case severe environments for surface charging detected at Los Alamos National Laboratory satellites during the years of 1990–2005 as binned by the definitions of four criteria developed by Matéo‐Vélez et al. (2018,https://doi.org/10.1002/2017sw001689) and the solar wind and Interplanetary Magnetic Field (IMF) parameters and geomagnetic activity indices are analyzed. The conducted analysis shows that only Auroral Electrojet/Auroral Lower index determines the highest risk for severe environments for surface charging to happen. The presence of a substorm with the southward turning pattern in IMFindicates that the environment can be severe for surface charging to occur but this environment will not depend on whether a substorm was moderate or intense. No clear dependence on IMFis found for risk to a severe environment to occur. Appearances of severe environments for surface charging do not necessarily require high values ofKp(Planetarische Kennziffer) and no storm is needed for such an event to be detected. Among solar wind parameters, solar wind velocityis directly related to the highest risk of severe environments, dependent on thevalue; and number densityis of no importance. Two criteria for severe environment events based on the enhancements of low energy particle fluxes exhibit clearer dependencies on the solar wind and IMF parameters and geomagnetic activity indices with more distinct patterns in their time history.

Continent‐Wide R1/R2 Current System and Ohmic Losses by Broad Dipolarization‐Injection Fronts

AbstractWe employ Magnetospheric Multiscale, Geostationary Operational Environmental and Los Alamos National Laboratory satellites, as well as the ground magnetometer networks over Greenland and North America to study a substorm on 9 August 2016 between 9 and 10 UT. We found that during the substorm two earthward flows, whose dipolarization‐injection fronts exceeded 6.5 and 4 Earth's radii (RE) in YGSM, impinged and rebounded from Earth's dipolar field lines at L=6–7 downtail, where L is the McIlwain number. The impingements and rebounds ended with a substorm current system of downward R1 and upward R2 currents which grew to azimuthally cover the whole North American continent. At the fronts, regions of enhanced negative j·E′ were formed and peaked toward the end of the impingements. These regions appeared to be conjugate with eastward moving aurora (along the growth phase arc and together with eastward drifting energetic electrons at geosynchronous equatorial orbit), which manifests ionospheric Ohmic losses.

Signatures of substorm related overshielding electric field at equatorial latitudes under steady southward IMF Bz during main phase of magnetic storm

During the geomagnetic storm periods, the convection electric field penetrates promptly to equatorial latitudes, causing an eastward electric field in the dayside ionosphere. Occasionally, the polarity of the dayside ionospheric electric field is inverted when the Interplanetary Magnetic Field (IMF) turns northward. In this paper, interesting observations of the strong westward electric field in the day side equatorial latitudes are presented, as evidenced by strong Counter Electrojet (CEJ) at Indian and Japanese sectors under the steady southward IMF Bz. The westward electric field perturbations are quite large with CEJ amplitude of ∼−120 nT over the Indian sector (14–15 December 2006) and ∼−220 nT for Japanese sector (7–8 November 2004). The plausible mechanisms for the observed overshielding electric fields under steady southward IMF Bz have been investigated in light of the possible role of substorm activity. The clear signatures of substorm were observed at geosynchronous particle flux measurements from LANL (Los Alamos National Laboratory) satellite and associated with sudden decrease in AL index. The observed variations of asymmetric ring current shows the enhancement of Partial Ring Current (PRC) at the dusk sector further supporting the substorm onset during that period which will probably enhance the overshielding due to increased Region 2 Field-Aligned Currents (R2 FACs). The observations of such significantly large amplitudes of CEJ associated with the substorm related overshielding events are sparse and the results bring out the important role of substorm onset and the development of PRC in accordance with the R2 FACs during intense magnetic storms which alter the day time equatorial electric field perturbations.

A Distributed Lag Autoregressive Model of Geostationary Relativistic Electron Fluxes: Comparing the Influences of Waves, Seed and Source Electrons, and Solar Wind Inputs

AbstractRelativistic electron flux at geosynchronous orbit depends on enhancement and loss processes driven by ultralow frequency (ULF) Pc5, chorus, and electromagnetic ion cyclotron (EMIC) waves, seed electron flux, magnetosphere compression, the “Dst effect,” and substorms, while solar wind inputs such as velocity, number density, and interplanetary magnetic field Bz drive these factors and thus correlate with flux. Distributed lag regression models show the time delay of highest influence of these factors on log10 high‐energy electron flux (0.7–7.8 MeV, Los Alamos National Laboratory satellites). Multiple regression with an autoregressive term (flux persistence) allows direct comparison of the magnitude of each effect while controlling other correlated parameters. Flux enhancements due to ULF Pc5 and chorus waves are of equal importance. The direct effect of substorms on high‐energy electron flux is strong, possibly due to injection of high‐energy electrons by the substorms themselves. Loss due to electromagnetic ion cyclotron waves is less influential. Southward Bz shows only moderate influence when correlated processes are accounted for. Adding covariate compression effects (pressure and interplanetary magnetic field magnitude) allows wave‐driven enhancements to be more clearly seen. Seed electrons (270 keV) are most influential at lower relativistic energies, showing that such a population must be available for acceleration. However, they are not accelerated directly to the highest energies. Source electrons (31.7 keV) show no direct influence when other factors are controlled. Their action appears to be indirect via the chorus waves they generate. Determination of specific effects of each parameter when studied in combination will be more helpful in furthering modeling work than studying them individually.

Electron dropout echoes induced by interplanetary shock: A statistical study

Abstract“Electron dropout echo” as indicated by repeated moderate dropout and recovery signatures of the flux of energetic electron in the outer radiation belt region has been investigated systematically. The electron moderate dropout and its echoes are usually found for higher‐energy (>300 keV) channel fluxes, whereas the flux enhancements are obvious for lower energy electrons simultaneously after the interplanetary shock arrives at the Earth's geosynchronous orbit. The electron dropout echo events are found to be usually associated with the interplanetary shocks arrival. The 104 dropout echo events have been found from 215 interplanetary shock events from 1998 to 2007 based on the Los Alamos National Laboratory satellite data. In analogy to substorm injections, these 104 events could be naturally divided into two categories: dispersionless (49 events) or dispersive (55 events) according to the energy dispersion of the initial dropout. It is found that locations of dispersionless events are distributed mainly in the duskside magnetosphere. Further, the obtained locations derived from dispersive events with the time‐of‐flight technique of the initial dropout regions are mainly located at the duskside as well. Statistical studies have shown that the effect of shock normal, interplanetary magnetic field Bz and solar wind dynamic pressure may be insignificant to these electron dropout events. We suggest that the ∼1 min electric field impulse induced by the interplanetary shock produces a more pronounced inward migration of electrons at the duskside, resulting in the observed duskside moderate dropout of electron flux and its consequent echoes.

On the origin of low‐energy electrons in the inner magnetosphere: Fluxes and pitch‐angle distributions

AbstractAccurate knowledge of the plasma fluxes in the inner magnetosphere is essential for both scientific and programmatic applications. Knowledge of the low‐energy electrons (approximately tens to hundreds of eV) in the inner magnetosphere is particularly important since these electrons are acted upon by various physical processes, accelerating the electrons to higher energies, and also causing their loss. However, measurements of low‐energy electrons are challenging, and as a result, this population has been somewhat neglected previously. This study concerns observations of low‐energy electrons made by the Helium Oxygen Proton Electron instrument on board the Van Allen Probes satellites and also observations from geosynchronous orbit made by the Magnetospheric Plasma Analyzer on board Los Alamos National Laboratory satellites. The fluxes of electrons from ~30 eV to 1 keV are quantified as a function of pitch‐angle, McIlwain L parameter, and local time for both quiet and active periods. Results indicate two sources for low‐energy electrons in this energy range: the low‐energy tail of the electron plasma sheet and the high‐energy tail of the dayside ionosphere. These populations are identified primarily as a result of their different pitch‐angle distributions. Field‐aligned outflows from the dayside ionosphere are observed at all L shells during quiet and active periods. Our results also demonstrate that the dayside electron field‐aligned fluxes at ~30 eV are particularly strong between L values of 6 and 7, indicating an enhanced source within the polar ionosphere.

Effects of ULF waves on local and global energetic particles: Particle energy and species dependences

AbstractAfter 06:13 UT on 24 August 2005, an interplanetary shock triggers large‐amplitude ultralow‐frequency (ULF) waves (|δB| ≥ 15 nT) in the Pc4–Pc5 wave band (1.6–9 mHz) near the noon geosynchronous orbit (6.6 RE). The local and global effects of ULF waves on energetic particles are observed by five Los Alamos National Laboratory satellites at different magnetic local times. The large‐amplitude ULF waves cause the synchronous oscillations of energetic electrons and protons (≥75 keV) at the noon geosynchronous orbit. When the energetic particles have a negative phase space density radial gradient, they undergo rapid outward radial diffusion and loss in the wave activity region. In the particle drift paths without strong ULF waves, only the rapidly drifting energetic electrons (≥225 keV) display energy‐dispersive oscillations and flux decays, whereas the slowly drifting electrons (<225 keV) and protons (75–400 keV) have no ULF oscillation and loss feature. When the dayside magnetopause is compressed to the geosynchronous orbit, most of energetic electrons and protons are rapidly lost because of open drift trajectories. The global and multicomposition particle measurements demonstrate that the effect of ULF waves on nonlocal particle flux depends on the particle energy and species, whereas magnetopause shadowing effect is independent of the energetic particle species. For the rapidly drifting outer radiation belt particles (≥225 keV), nonlocal particle loss/acceleration processes could also change their fluxes in the entire drift trajectory in the absence of “Dst effect” and substorm injection.

An improved empirical model of electron and ion fluxes at geosynchronous orbit based on upstream solar wind conditions

AbstractA 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.

Comparison of simulated and observed trapped and precipitating electron fluxes during a magnetic storm

The ability to accurately model precipitating electron distributions is crucial for understanding magnetosphere-ionosphere-thermosphere coupling processes. We use the magnetically and electrically self-consistent Rice Convection Model-Equilibrium (RCM-E) of the inner magnetosphere to assess how well different electron loss models can account for observed electron fluxes during the large 10 August 2000 magnetic storm. The strong pitch angle scattering rate produces excessive loss on the morning and dayside at geosynchronous orbit (GEO) compared to what is observed by a Los Alamos National Laboratory satellite. RCM-E simulations with parameterized scattering due to whistler chorus outside the plasmasphere and hiss inside the plasmasphere are able to account simultaneously for trapped electron fluxes at 1.2 keV to ~100 keV observed at GEO and for precipitating electron fluxes and electron characteristic energies in the ionosphere at 833 km measured by the NOAA 15 satellite.

An empirical model of electron and ion fluxes derived from observations at geosynchronous orbit

Knowledge of the plasma fluxes at geosynchronous orbit is important to both scientific and operational investigations. We present a new empirical model of the ion flux and the electron flux at geosynchronous orbit (GEO) in the energy range ~1 eV to ~40 keV. The model is based on a total of 82 satellite-years of observations from the Magnetospheric Plasma Analyzer instruments on Los Alamos National Laboratory satellites at GEO. These data are assigned to a fixed grid of 24 local-times and 40 energies, at all possible values of Kp. Bi-linear interpolation is used between grid points to provide the ion flux and the electron flux values at any energy and local-time, and for given values of geomagnetic activity (proxied by the 3-hour Kp index), and also for given values of solar activity (proxied by the daily F10.7 index). Initial comparison of the electron flux from the model with data from a Compact Environmental Anomaly Sensor II (CEASE-II), also located at geosynchronous orbit, indicate a good match during both quiet and disturbed periods. The model is available for distribution as a FORTRAN code that can be modified to suit user-requirements.

In situ signatures of residual plasmaspheric plumes: Observations and simulation

AbstractWe compare in situ observations of the Los Alamos National Laboratory (LANL) Magnetospheric Plasma Analyzers with output of a dynamic, plasmapause test particle (PTP) simulation for the moderately disturbed interval 18–20 January 2000. In the model, weakly enhanced convection on 18 January creates a narrow drainage plume (plume A) that wraps completely around the main torus. Moderate convection on 19 January triggers significant plasmaspheric erosion, forming a second plume (B) that coexists with the narrow, wrapped, residual plume A. We fly three virtual LANL satellites through the simulation domain. The observations are globally consistent with the PTP simulation; LANL data contain several intervals of plume plasma in the model's predicted magnetic local time (MLT) sector. The modeled durations of plume sector transits are in good agreement with the LANL data. On a subglobal scale, the MLT widths and timings of the simulated plumes do not precisely agree with observations. However, several observation intervals exhibit good morphological agreement with virtual spacecraft signatures of two distinct, coexisting plumes (A and B). The fine‐scale structure in the PTP model arises from the merging of residual plume A with the newer plume B. Plume merging is one theoretical means of generating fine structure in the plasmasphere: during multiple cycles of erosion and recovery, successive layers of wrapped, residual plumes can merge with newer plumes, creating layers of filamentary density structure. The model‐data comparisons suggest that the plasmaspheric density distribution may preserve some memory of prior epochs of erosion and recovery.

Sawtooth-substorm connections: A closer look

[1] This paper seeks to improve understanding of sawtooth events (STEs) that occur during the main phases of geomagnetic storms. We consider the dynamics of diverse space environments encountered during a magnetic storm on 24 March 2002 when four STEs were identified in energetic particle fluxes measured by Synchronous Orbit Particle Analyzers on Los Alamos National Laboratory satellites. Over the reported interval, 28 substorms were identified in magnetometer traces obtained via the SuperMAG international collaboration. Magnetic inclination variations sampled by the Geostationary Operational Environment Satellites 8 and 10 on the nightside indicate that STEs coincided with substorms marked by strong and prolonged dipolarizations. Significantly, the four STEs were accompanied by partial recoveries of the SYM-H index. Two SuperMAG substorms were marked by weak dipolarizations and energetic particle flux increases. The remaining 22 substorms showed no such signatures near 6.6 RE. We regard the latter SuperMAG events as indicating intensifications of the DP 2 current system driven by episodically enhanced reconnection at the distant X line. Presented data are shown to be consistent with the conjecture of Huang et al. (2009) that STEs occur only after open flux in the magnetotail exceeds a critical level near 109 Wb. During STEs, significant quantities of open flux were removed from the magnetotail at near-Earth reconnection lines. It took ~3 h to eject plasmoids and replenish open flux in the magnetotail to a critical level via continued dayside merging, thereby driving quasi-cyclic STE occurrences.

Statistical properties of the surface‐charging environment at geosynchronous orbit

AbstractBased on 13 years of data from the Magnetospheric Plasma Analyzers on six Los Alamos National Laboratory (LANL) geosynchronous satellites, the statistical behavior of environmental conditions that cause strong surface charging on the satellites is examined. Analysis of the Magnetospheric Plasma Analyzers data reveals the electron energy range (~5–10 keV) and threshold flux (1.4×103 cm–2 s–1 sr–1 eV–1 at 8 keV) that are most closely associated with satellite surface charging. We also find that the average ambient electron temperature in the plasma sheet correlates with the observed magnitude of the surface potential on the LANL satellites. Analysis of the statistical occurrence rates of (1) the observed surface potential on the LANL satellites, (2) 8 keV electron fluxes above the threshold, and (3) elevated values of the average electron temperature all reveal that an enhanced surface charging probability exists (a) during higher values of Kp, (b) in the local time range from premidnight through dawn, (c) during equinox seasons, and (d) during the declining phase of the solar cycle. With the exception of the solar cycle dependence, these are the same statistical dependences found by Choi et al. (2011) in the satellite anomaly database they examined. The local time dependence of those anomalies is a particularly strong diagnostic of surface charging as a probable cause of a significant number of them.

Geomagnetic activity triggered by interplanetary shocks

Interplanetary (IP) shocks can greatly disturb the Earth's magnetosphere, causing the global dynamic changes in the electromagnetic fields and the plasma. In order to investigate this, we have systematically analyzed 106 IP shock events based on OMNI data, GOES, and Los Alamos National Laboratory satellite observations during 1997−2007. It is revealed that the median value of IMF Bz keeps negative/positive prior to shock arrival and becomes more negative/positive following the shock arrival. The statistical analysis shows that IP shocks with southward interplanetary magnetic field (IMF) (46%) are likely to increase AE (AL, AU) and PC indices significantly. The amplitude of AE index increases from 200 to 600 nT, AU from 100 to 200 nT, AL from 50 to 400 nT, and PC from 1.5 to 3 approximately in 10 min, which could be a signature of geomagnetic activity/substorms onset (or substorm further intensification). Meanwhile, there is a strong injection of energetic electrons in the dawn region following the shock arrival and a strong depletion in the dusk region 30 min later, showing a clear dawn‐dusk asymmetry. On the other hand, there is only the typical shock compression effect for IP shocks with northward IMF (54%). The median value of AE index increased from 80 to 150 nT, AU from 50 to 90 nT, AL index decreased from −30 to −40 nT, and PC index increased from 0.6 to 1.2 in ∼10 min following the shock arrival. Both individual cases and statistical studies indicate that the magnetosphere‐ionosphere system must be preconditioned for a substorm‐like geomagnetic activity to be triggered by an IP shock with southward IMF impact, whereas IP shock with northward IMF precondition shows only compression effect.

Observation and modeling of the injection observed by THEMIS and LANL satellites during the 23 March 2007 substorm event

During the encounter of a substorm on 23 March 2007, the THEMIS constellation observed energetic particle injections and dipolarizations in the premidnight sector. Clear injection and dipolarization signatures were observed during the main intensification by three probes (A, B, and D) in the region around 11 RE and 2100 local time (LT). THEMIS C, which was leading in the constellation at 8.3 RE, also observed a clear injection signature, but the dipolarization was not so clear. From the timing based on these observations, a fast westward expanding ion injection and dipolarization front was identified. In combination with the energetic particle observations from Los Alamos National Laboratory (LANL) geosynchronous satellites, the particle injection seemed to initiate between 2100 and 0100 LT. This event provides an excellent opportunity to examine the dipolarization and particle injection processes beyond geosynchronous orbit and over a wide LT range. We model this injection event by means of test particle simulation, setting up an initial particle distribution and sending an earthward dipolarization‐like pulse from the tail that also expands azimuthally, then recording the ions and electrons at the various satellite locations. Most features of the injected particles are reproduced by the test particle simulation. These include not only the earthward injections but also the fast westward expansion of the injection, as well as the timing of the injections as observed among different satellites that made the observations. On the basis of the observations and the simulation results, we suggest that this substorm injection was initiated around 2300 LT, farther down the tail, and propagated radially inward and expanded azimuthally.

Dynamical property of storm time subauroral rapid flows as a manifestation of complex structures of the plasma pressure in the inner magnetosphere

During the intense magnetic storm of 15 December 2006, the midlatitude Super Dual Auroral Radar Network (SuperDARN) Hokkaido radar observed a dynamical character of rapid, westward flows at 50–56 magnetic latitude. The simulation that couples the inner magnetosphere and the subauroral ionosphere was performed using a realistic boundary condition of the hot ion distribution determined from four Los Alamos National Laboratory satellites at 6.6 RE. The following results are obtained using the simulation: (1) In general, morphology of the azimuthal component of the simulated ionospheric plasma flow is consistent with that known as the subauroral polarization stream (SAPS), (2) an increase in the hot ion density in the plasma sheet results in the temporal reduction and subsequent intensification of the rapid flow at certain subauroral latitudes with a delay of ∼40 min, and (3) influence of the plasma sheet temperature on the rapid flow is not evident. The simulated line‐of‐sight velocity is compared with that obtained by the SuperDARN Hokkaido radar. Agreement between them is found in terms of the temporal and spatial variations of the rapid flows as well as the flow velocity. It is suggested that the dynamical character of the subauroral plasma flow is a direct manifestation of the plasma pressure distribution in the inner magnetosphere (the ring current) especially during the magnetic storm.

Number of Arcs Estimated on Solar Array of a Geostationary Satellite

Plasma parameters of geosynchronous orbit measured by Los Alamos National Laboratory satellites are analyzed statistically. For each set of plasma parameters, charging analysis is carried out, taking a geostationary satellite representing a typical telecommunication satellite as an example. The number of expected trigger arcs on a solar array is calculated based on the charging duration with severe inverted potential gradient conditions expected in orbit. Using the number of trigger arcs, an appropriate duration of electrostatic discharge ground test is proposed to test the insulation strength against sustained arc phenomena.

A radiation belt‐ring current forecasting model

A radiation belt‐ring current (RB‐RC) forecasting model is presented. This model solves the convection‐diffusion equation of plasma distribution in the 10 keV to a few MeV range. There are four major auxiliary components to the RB‐RC model: a global magnetic field model, an electric field model, a plasma sheet model (plasma source), and a radial diffusion model. All four components are driven by solar wind and interplanetary magnetic field conditions. In this paper, a brief description of the model and input parameters is given. This model has been used to simulate several geomagnetic storms. In particular, the effects of the inductive electric field on the evolution of the radiation belt electron fluxes are investigated in detail via a case study of the 12 August 2000 storm. It is found that, in general, the inductive electric field arising from the time‐varying magnetic field can enhance the flux level around geosynchronous orbit during the recovery phase of the storms. The model is validated through comparing the simulation results with the Los Alamos National Laboratory satellite measurements. Further refinement and improvement of the model is also discussed.