Electron, Proton, And Alpha Monitor Research Articles

Impacts on Proton Fluxes Observed During Different Interplanetary Conditions

Interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs) are the major characteristic events of the solar wind (SW). We used proton flux data with different energy levels provided by the Low Energy Magnetic Spectrometers (LEMS) 120 system of the Electron, Proton and Alpha Monitor (EPAM) for studying different ICME-driven and CIR-driven storms. Our main aim was to find, from the observational results, the nature of the proton flux during solar storms driven by different mechanisms that, in our cases, are related to ICMEs and CIRs, in the interplanetary regions. We analyzed the different parameters provided by the LEMS 120 system and compared them during the different storm types and during a selected quietest day as well. We studied four events: a geomagnetically quiet day, two ICME-driven storms and one CIR-driven storm. We also analyzed the interplanetary magnetic field (IMF) magnitude (B) and the different SW parameters during all these events. We observed that both the prolonged particle precipitations during CIRs and the intense particle precipitations during ICMEs result in the different nature of the fluxes with different energy levels compared with other parameters such as B, and the SW velocity (V). Our quiet-period results show that there is a strong correlation between the higher energy proton fluxes and B and V and a weak correlation in the case of lower energy protons. Our storm-time results demonstrate that when the storm is either driven by ICMEs or CIRs, the lower energy protons also starts to show positive correlations with B and V with a 0 min time lag (TA) during ICMEs and with a ≈−100min TA during CIRs. During the quiet day, the proton flux observed was due to the perturbations created by ionization and the higher energy of the protons sufficiently weakened. Whereas, the CME speed, the preceding CMEs, and the presence of pre-existing solar energetic particles (SEPs) in the ambient medium, the makeup of CIR-related winds, and the nature of precipitation during both ICMEs and CIRs caused the proton fluxes with different energy levels during storm times.

Deep dielectric charging and breakdown of lunar polar regolith

Galactic cosmic rays (GCRs) and solar energetic particles (SEPs) penetrate the regolith (layer of soil and dust) covering the Moon's surface and cause deep dielectric charging. To gain insight into this process, we have developed a data-driven, deep dielectric charging model using data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER), which is onboard the Lunar Reconnaissance Orbiter (LRO), and the Electron, Proton, and Alpha Monitor (EPAM) on the Advanced Composition Explorer (ACE). The model results indicate that GCRs produce a persistent electric field (∼700 V m-1) within the top tens of centimeters of regolith, while large SEP events could potentially generate episodic subsurface electric fields (≥ 106 V m-1) capable of causing dielectric breakdown within the top millimeter of regolith. We also propose that this “breakdown weathering” may have significantly affected the regolith in the Moon's permanently shadowed regions (PSRs).

SIMULATION MODELING OF INTERPLANETARY SHOCKS ARRIVAL TIME PREDICTION ON HISTORICAL DATA SET

An approach to prediction of the arrival time of interplanetary shocks using neural networks based on the data gathered from single EPAM (Electron, Proton and Alpha Monitor) channel of NASA’s ACE (Advanced Composition Explorer) spacecraft is proposed in this paper. A short description of ACE spacecraft and the data, published online on the appropriate web-site, are considered. A data choice to fulfill a prediction of interplanetary shocks is proven and structure of neural network is described. The results of simulation modeling in MATLAB are considered in the end of the paper.

Enhancement of solar wind low-energy energetic particles as precursor of geomagnetic disturbance in operational geomagnetic forecast

A study of the relationship between solar wind low-energy energetic particles using data from the Electron, Proton, and Alpha Monitor (EPAM) onboard the Advanced Compositional Explorer spacecraft (ACE) and geomagnetic activity using data from Canadian magnetic observatories in Canada’s polar cap, auroral zone, and subauroral zone was carried out for a period spanning 1997–2005. Full halo coronal mass ejections (CMEs) were used to gauge the initial particle enhancements and the subsequent geomagnetic activity. It was found that maximum geomagnetic activity is related to maximum particle enhancements in a non-linear fashion. Quadratic fit of the data results in expressions that can be easily used in an operational space weather setting to forecast geomagnetic disturbance quantitatively. A superposed epoch analysis shows increase in particle flux level starts hours before geomagnetic activity attains its peak, affirming the precursory nature of EPAM particles for the impending geomagnetic impact of CME. This can supplement the decision process in formulating geomagnetic warning after the launch of CME from the Sun but before the arrival of shock at Earth. The empirical relationships between solar wind low-energy energetic particles and geomagnetic activity revealed in this statistical study can be easily codified, and thus utilized in operational space weather forecast to appraise the geoeffectiveness of the CME and to provide a quantitative forecast for maximum geomagnetic activity in Canada’s polar cap, auroral zone, and subauroral zone after the occurrence of a CME.

Statistical study of low‐energy heliosphere particle fluxes from 1.4 to 5 AU over a solar cycle

Throughout the entire Ulysses mission, the Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energies (HI‐SCALE) has collected measurements of low‐energy interplanetary ions and electrons. Time series of electron, proton, and ion fluxes have been obtained since 1990. We present statistical studies of high‐resolution ion and electron energy spectra (∼50 keV to ∼5 MeV) as measured by the HI‐SCALE instrument on the Ulysses spacecraft over a time interval longer than a solar cycle (1990 to 2004). Ulysses is the only spacecraft that continually measured the inner (∼1.4 to ∼5 AU) heliosphere particle population during these years. The data thus provide measures of the lower‐energy population of particles that a spacecraft traveling outward from Earth would have encountered and that also could have impacted the atmosphere and surface of Mars and of its satellites during this interval. Comparisons of Ulysses particle fluxes with those from the Electron, Proton, and Alpha Monitor (EPAM) instrument on the Advanced Composition Explorer (ACE) spacecraft (the HI‐SCALE backup instrument) have shown that azimuthal and heliolatitude dependencies of particle fluxes in the inner heliosphere following solar events are not as extreme as might be expected. Thus the Ulysses measurements, while taken over a range of heliolatitudes, can provide important statistical information that can be used to estimate the low‐energy radiation dosages and potential sputtering fluxes to planetary surfaces and to heliosphere spacecraft surfaces and solar arrays over a solar cycle.

The Radio–Coronal Mass Ejection Event on 2001 April 15

On 2001 April 15, the Nancay radioheliograph observed fast-moving, expanding loops in images taken in the wavelength range between 164 and 432 MHz. We were able to follow the progression of the radio loops, starting from a few tenths to more than 1 R☉ above the solar limb, with a time cadence of order seconds. The loops seen in radio agree very well with the features of the coronal mass ejection (CME) seen later, more than 2.5 R☉ above the limb, in white-light images by the Large Angle Spectrometric Coronagraph (LASCO) experiment on board the Solar and Heliospheric Observatory (SOHO) spacecraft. The event is well associated with an energetic electron event seen by the Electron, Proton, and Alpha Monitor (EPAM) experiment on board the Advanced Composition Explorer (ACE) spacecraft. A detailed transport model for the electrons shows that, not only the inferred onset at the Sun, but also the duration of the particle release, are similar for the radio loop and the in situ electron event detected near the Earth.

Forecasting space weather: Predicting interplanetary shocks using neural networks

We are developing a system to predict the arrival of interplanetary (IP) shocks at the Earth. These events are routinely detected by the Electron, Proton, and Alpha Monitor (EPAM) instrument aboard NASA’s ACE spacecraft, which is positioned at Lagrange Point 1 (L1). In this work, we use historical EPAM data to train an IP shock forecasting algorithm. Our approach centers on the observation that these shocks are often preceded by identifiable signatures in the energetic particle intensity data. Using EPAM data, we trained an artificial neural network to predict the time remaining until the shock arrival. After training this algorithm on 37 events, it was able to forecast the arrival time for 19 previously unseen events. The average uncertainty in the prediction 24 h in advance was 8.9 h, while the uncertainty improved to 4.6 h when the event was 12 h away. This system is accessible online, where it provides predictions of shock arrival times using real-time EPAM data.

Revisiting the Origin of Impulsive Electron Events: Coronal Magnetic Restructuring

We revisit the impulsive beamlike particle events detected in situ from 1997 to 2000 by the Electron, Proton, and Alpha Monitor (EPAM) experiment on the Advanced Composition Explorer spacecraft. We study in detail a subset of events for which there are radio coronal observations from the Nancay Radioheliograph. EPAM measures electrons in the energy range from 40 to 300 keV over a wide range of look directions and with better than 1 minute time resolution, while the Nancay radioheliograph provides images of the solar corona at five different frequencies with time cadence of eight images per second and per frequency. The radio images are complemented with spectral information from a series of radiospectrographs over a wide frequency range (from dm to km wavelengths), white-light coronagraphic images from the Large Angle Spectroscopic Coronagraph (LASCO) on the the Solar and Heliospheric Observatory (SOHO) spacecraft, and EUV images from the Extreme Ultraviolet Imaging Telescope (EIT), also on SOHO. We separate the particle events according to their associated radio emissions in the meter to decameter wavelengths, in radio-simple (only type III bursts) and radio-complex (also type II bursts and/or continua). The electron events in the radio-simple category have rather short durations, are very weak, and show essentially no delay between the onset of type III emission and the inferred release time for the energetic electrons. The electron events in the radio-complex category present variable delays between the onset of type III emission and the inferred release time for the energetic electrons. The inferred release time for the particles in the radio-complex category always coincides with the onset or major changes in the complex radio emissions; this good association suggests that the coronal processes involved in the radio emissions are at the origin of the electron acceleration. The timing and spectral characteristics of the radio emissions, when compared with the properties of the particles seen at EPAM, and the white-light information from LASCO, strongly support an acceleration process in the corona, at variable heights and below the leading edge of the associated coronal mass ejection. The coronal restructuring put in evidence by the radio signatures is the simplest explanation for the origin of those energetic particles.

Solar origin of near-relativistic impulsiveelectron events

Abstract There is increasing evidence suggesting that coronal acceleration supplies at least part of the particles observed during solar energetic particle events, yet coronal processes tend to be mostly disregarded in these studies. This is often due to the fact that the coronal restructuring in the early development of the associated flare and/or coronal mass ejection event is extremely fast (on the order of a few minutes) and can encompass most of the solar disk, thus requiring a full disk solar imager with very high time-cadence, and wide spectral coverage. An important subset of the energetic particle events are the near-relativistic impulsive electron events detected near Earth: their onsets can be traced back to a release time in the low corona with accuracies on the order of a couple of minutes. We investigate a series of impulsive electron events from 1998 to 2001 using energetic electron data measured in situ by the Electron, Proton, and Alpha Monitor (EPAM) experiment on the Advanced Composition Explorer (ACE) spacecraft, and radio coronal observations from the Nanqay Radioheliograph, the Decametric Array from Nanqay and the WAVES experiment on the WIND spacecraft. EPAM measures electrons in the energy range from 40 to 300 keV over a wide range of look directions and with better than 1 minute time resolution, while the Nancay radioheliograph provides images of the solar corona at 5 different frequencies with time cadence of 8 images per second and per frequency. This study focuses on the events which correspond to a delay, between the inferred injection times of the electrons at the Sun, and the electromagnetic emissions from flares, of at least 5 minutes. Radio signatures are found near the estimated time of the electron release for each of the events. The timing and spectral characteristics of the radio emissions, when compared with the properties of the particles seen at EPAM, strongly support an acceleration process in the corona but at highly variable heights from one event to the other.

Solar origin of near-relativistic impulsive electron events

Abstract There is increasing evidence suggesting that coronal acceleration supplies at least part of the particles observed during solar energetic particle events, yet coronal processes tend to be mostly disregarded in these studies. This is often due to the fact that the coronal restructuring in the early development of the associated flare and/or coronal mass ejection event is extremely fast (on the order of a few minutes) and can encompass most of the solar disk, thus requiring a full disk solar imager with very high time-cadence, and wide spectral coverage. An important subset of the energetic particle events are the near-relativistic impulsive electron events detected near Earth: their onsets can be traced back to a release time in the low corona with accuracies on the order of a couple of minutes. We investigate a series of impulsive electron events from 1998 to 2001 using energetic electron data measured in situ by the Electron, Proton, and Alpha Monitor (EPAM) experiment on the Advanced Composition Explorer (ACE) spacecraft, and radio coronal observations from the Nanqay Radioheliograph, the Decametric Array from Nanqay and the WAVES experiment on the WIND spacecraft. EPAM measures electrons in the energy range from 40 to 300 keV over a wide range of look directions and with better than 1 minute time resolution, while the Nancay radioheliograph provides images of the solar corona at 5 different frequencies with time cadence of 8 images per second and per frequency. This study focuses on the events which correspond to a delay, between the inferred injection times of the electrons at the Sun, and the electromagnetic emissions from flares, of at least 5 minutes. Radio signatures are found near the estimated time of the electron release for each of the events. The timing and spectral characteristics of the radio emissions, when compared with the properties of the particles seen at EPAM, strongly support an acceleration process in the corona but at highly variable heights from one event to the other.

The Acceleration and Release of Near‐relativistic Electrons by Coronal Mass Ejections

We have examined transient coronal activity observed by the Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph Experiment (LASCO) around the release time of beams of near-relativistic electrons (~40-300 keV) observed by the Advanced Composition Explorer (ACE)/Electron, Proton, and Alpha Monitor (EPAM) at 1 AU. The electron beams are strongly associated with coronal mass ejections (CMEs) emitted from near the Sun's western limb, although the converse is not true; many more west hemisphere CMEs are seen by LASCO than are relativistic electron beams seen by ACE/EPAM. However, when they are present, strong beams of electrons may be used to infer reliably the actual solar release time as they propagate scatter free. Fifty-two electron beams were observed from 1997 September to 2000 September at times of LASCO observations. Of these, there were 47 observations of an associated coronal transient, of which 33 were classical CMEs, as distinct from blobs and jets. We were able to extrapolate the height-time plot back to a nominal 1 R☉, to estimate a CME launch time. All but two of the CMEs were seen in projection off the west solar limb. For 37 events there was an associated soft X-ray event, the majority of which were from western active regions. All electron events were accompanied by decametric type III emission consistent with electron beams having exciter energies of around a few keV. The near-relativistic electron injection time was typically delayed by ~20 minutes from the CME launch time and greater than ~10 minutes after the onset of the electromagnetic radio and X-ray signatures of the flare (when present). Therefore, the near-relativistic electrons that must be present to produce the chromospheric electromagnetic emission do not escape promptly (at least at detectable intensities). The radial distance of most CMEs at the electron release time was between 1.5 and 3.5 R☉. Both the peak electron intensity and the spectral hardness of the electrons were positively correlated with the CME speed, a signature of shock acceleration. We therefore suggest that most of the near-relativistic electrons seen by ACE/EPAM are accelerated by the shock driven by the coronal transient and are released at a radial distance around 2-3 R☉.

The release of near‐relativistic electrons from the Sun

Coronal flares are perhaps the most prolific source of low‐energy electrons (2–10 keV) detected in the interplanetary medium and are occasionally seen at higher energies ≥100 keV. We have searched 38–315 keV electron data from the Electron, Proton, and Alpha Monitor (EPAM) on the ACE spacecraft throughout 1998 for such events and focus upon three prolonged bursts of electrons on 5 May 1998. We find that certainly one and probably all three bursts originated in the corona several R⊙ above the photosphere. They were composed of multiple injections of electrons and were possibly quasi‐continuously released over almost 24 hours, periodically interrupted at ACE by changes in solar wind speed and magnetic connection to the Sun. We postulate that the presence of seed electrons in the corona from a chromospheric flare 3 days earlier played a role in the acceleration of these electrons to energies of ≥100 keV.

Solar Origin of a Series of Well‐collimated Electron Events

We investigate the solar origin and propagation of a series of well-collimated energetic electron events on 1997 November 28, measured in situ by the Electron, Proton, and Alpha Monitor (EPAM) experiment on the Advanced Composition Explorer (ACE) spacecraft. EPAM measures electrons in the energy range from 40 to 300 keV over a wide range of look directions and with better than 1 minute time resolution. During the events in our study, the particles are strongly collimated along the magnetic field. As such, these near-relativistic (beta = 0.4-0.7) particles tend to be scatter free; their observed arrival at ACE provides a good estimate of the release time back to the Sun. EPAM results are extended to 20 keV using energetic electron data from the Three-Dimensional Plasma Analyzer (3DP) experiment on the Wind spacecraft. We combine these observations with fast imaging of the solar corona in the meter wave domain, provided by the Nancay radioheliograph, and dynamic spectral information from the WAVES experiment on the Wind spacecraft. Together, this complement of observations of solar energetic particle events provides insight into the onset times and sites of particle acceleration in the low corona. The imaging observations at metric radio frequencies show three series of similar events off the west limb of the Sun that extend into interplanetary type III bursts. The third event corresponds only to a strong in situ particle event. During this time period, the coronagraphic observations from the Large Angle and Spectrometric Coronagraph experiment on the Solar and Heliospheric Observatory reveal a dimming and some morphological changes in the vicinity of the injection site, suggesting the opening of the magnetic field. We find that for the strongest event, the onset times for the energetic particles measured at the spacecraft reveal a dispersion in the inferred release times back at the Sun versus energy. The onset times measured for electrons with energies above 60 keV are not compatible with the release time back at the Sun inferred from particles of lower energies. This dispersion can be successfully explained by the radio data: the radio observations reveal two successive energetic electron injections separated by a few minutes. The observations thus show that there is a later release of the particles detected in situ at higher energies and that the origin of the phenomenon is in the low corona.

Electron, Proton, and Alpha Monitor on the Advanced Composition Explorer Spacecraft

The Electron, Proton, and Alpha Monitor (EPAM) is designed to make measurements of ions and electrons over a broad range of energy and intensity. Through five separate solid-state detector telescopes oriented so as to provide nearly full coverage of the unit-sphere, EPAM can uniquely distinguish ions (Ei≳50 keV) and electrons (Ee≳40 keV) providing the context for the measurements of the high sensitivity instruments on ACE. Using a ΔE×E telescope, the instrument can determine ion elemental abundances (E≳0.5 MeV nucl−1). The large angular coverage and high time resolution will serve to alert the other instruments on ACE of interesting anisotropic events. The experiment is controlled by a microprocessor-based data system, and the entire instrument has been reconfigured from the HI-SCALE instrument on the Ulysses spacecraft. Inflight calibration is achieved using a variety of radioactive sources mounted on the reclosable telescope covers. Besides the coarse (8 channel) ion and (4 channel) electron energy spectra, the instrument is also capable of providing energy spectra with 32 logarithmically spaced channels using a pulse-height-analyzer. The instrument, along with its mounting bracket and radiators weighs 11.8 kg and uses about 4.0 W of power. To demonstrate some of the capabilities of the instrument, some initial performance data are included from a solar energetic particle event in November 1997.