Solar Energetic Particle Fluxes Research Articles

Are Sporadic Plasma Layers at 90 km in the Mars Ionosphere Produced by Solar Energetic Particle Events

AbstractLayers of dayside ionospheric plasma have been sporadically observed on Mars at 90 km altitude. Several causes for these layers have been proposed. Here we test the hypothesis that solar energetic particle (SEP) events produce these layers. Several independent lines of evidence show that SEP events do increase plasma densities at low altitudes. We compare the occurrence of low‐altitude plasma layers to a proxy for the flux of solar energetic particles at Mars. For the ionospheric layers, we use 71 instances of low‐altitude plasma layers found in 5,600 electron density profiles acquired by Mars Global Surveyor. For the proxy for solar energetic particle flux, we use the flux recorded in the highest energy channel of the Mars Global Surveyor Electron Reflectometer. We find that these low‐altitude plasma layers are not significantly more likely to occur during SEP events.

Non-interacting coronal mass ejections and solar energetic particles near the quadrature configuration of Solar TErrestrial RElations Observatory

We present our results on the correlation of non-interacting coronal mass ejections (CMEs) and solar energetic particles (SEPs). A statistical analysis was conducted on 25 SEP events and the associated CME and flare during the ascending phase of solar cycle 24, i.e., 2009–2013, which marks the quadrature configuration of Solar TErrestrial RElations Observatory (STEREO). The complete kinematics of CMEs is well studied near this configuration of STEREO. In addition, we have made comparison studies of STEREO and SOlar and Heliospheric Observatory results. It is well known that the CME speeds and SEP intensities are closely correlated. We further examine this correlation by employing instantaneous speeds (maximum speed and the CME speed and Mach number at SEP peak flux) to check whether they are a better indicator of SEP fluxes than the average speed. Our preliminary results show a better correlation by this approach. In addition, the correlations show that the fluxes of protons in energy channel >10 MeV are accelerated by shock waves generated by fast CMEs, whereas the particles of >50 MeV and >100 MeV energy bands are mostly accelerated by the same shock waves but partly by the associated flares. In contrast, the X-ray flux of solar flares and SEP peak flux show a poor correlation.

Numerical simulation and data analysis of the 23 July 2012 SEP event observed by ACE, STEREO-A, and STEREO-B

An extremely powerful, superfast interplanetary coronal mass ejection (ICME) from the Sun on 23 July 2012 was detected by widely separated multiple spacecraft, namely STEREO-A, STEREO-B, and ACE, together with the ICME-driven shock and associated solar energetic particles (SEPs). We use the Parker spiral magnetic field model to analyze the relationship between the propagation of the shock and the SEP flux. Furthermore, we simulate the SEP event by numerically solving the three-dimensional focused transport equation of SEPs considering the shock as the moving source of energetic particles. To deal with the fact that protons and electrons behave completely differently for both parallel and perpendicular diffusion, for simplicity, we use the same diffusion model format for the simulations of protons and electrons but with different parameters. We find that the analysis can qualitatively explain the important features of the SEP flux observed by the multiple spacecraft simultaneously. In addition, the numerical results for both energetic protons and electrons approximately agree with multi-spacecraft observations.

Spectral Structures of Type II Solar Radio Bursts and Solar Energetic Particles

Abstract We investigated the relationship between the spectral structures of type II solar radio bursts in the hectometric and kilometric wavelength ranges and solar energetic particles (SEPs). To examine the statistical relationship between type II bursts and SEPs, we selected 26 coronal mass ejection (CME) events with similar characteristics (e.g., initial speed, angular width, and location) observed by the Large Angle and Spectrometric Coronagraph, regardless of the characteristics of the corresponding type II bursts and the SEP flux. Then, we compared associated type II bursts observed by the Radio and Plasma Wave Experiment on board the Wind spacecraft and the SEP flux observed by the Geostationary Operational Environmental Satellite orbiting around the Earth. We found that the bandwidth of the hectometric type II bursts and the peak flux of the SEPs has a positive correlation (with a correlation coefficient of 0.64). This result supports the idea that the nonthermal electrons of type II bursts and the nonthermal ions of SEPs are generated by the same shock and suggests that more SEPs may be generated for a wider or stronger CME shock with a longer duration. Our result also suggests that considering the spectral structures of type II bursts can improve the forecasting accuracy for the peak flux of gradual SEPs.

The Pivot Energy of Solar Energetic Particles Affecting the Martian Surface Radiation Environment

Abstract Space radiation is a major risk for humans, especially on long-duration missions to outer space, e.g., a manned mission to Mars. Galactic cosmic rays contribute a predictable radiation background; the main risk is due to the highly variable and currently unpredictable flux of solar energetic particles (SEPs). Such sporadic SEP events may induce acute health effects and are thus considered a critical mission risk for future human exploration of Mars. Therefore, it is of the utmost importance to study, model, and predict the surface radiation environment during such events. It is well known that the deep-space SEP differential energy spectrum at high energies is often given by a power law. We use a measurement-validated particle transport code to show that, for large SEP events with proton energy extending above ∼500 MeV with a power-law distribution, it is sufficient to measure the SEP flux at a pivot energy of ∼300 MeV above the Martian atmosphere to predict the dose rate on the Martian surface. In conjunction with a validation by in situ measurements from the Martian surface, this remarkable simplification and elegant quantification could enable instant predictions of the radiation environment on the surface of Mars upon the onset of large SEP events.

Onset of a CME-Related Shock Within the Large-Angle Spectrometric Coronagraph (LASCO) Field of View

We investigated the onset of a CME-related shock within the Large-Angle Spectrometric Coronagraph (LASCO) field of view (FOV). To detect the first moment of the shock onset, we found a CME on 17 July 2012 that formed at a relatively high altitude and moved with slow acceleration. We examined the possible mechanisms of shock generation. It was shown that bow-shock and piston-shock mechanisms can participate in shock generation, either at different stages of CME movement, or simultaneously. This event has been found to be accompanied by generation of solar energetic particles (SEP). We concluded that, at their initial stage, the source of SEP fluxes may be a solar flare, while the later dramatic increase in the flux of fast protons may be due to their generation in a CME-driven shock.

On the response of Martian Ionosphere to the Passage of a Corotating Interaction Region: MAVEN Observations

AbstractThe response of Martian ionosphere to the passage of corotating interaction region (CIR) of June 2015 is studied using observations from several instruments aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. An intense CIR arrived at Mars on 22 June 2015, during which the upstream solar wind and interplanetary magnetic field conditions were monitored by the Solar Wind Ion Analyzer (SWIA), Solar Wind Electron Analyzer (SWEA), Solar Energetic Particle (SEP), and Magnetometer (MAG) instruments aboard MAVEN. The CIR event was characterized by enhancements in solar wind density, velocity, and dynamic pressure, and increased and fluctuating interplanetary magnetic field and was associated with enhanced fluxes of Solar Energetic Particles. The Langmuir Probe and Waves (LPW) instrument onboard MAVEN provided the ionospheric observations such as electron density and electron temperature during this period. The dayside ionosphere is significantly compressed only near the peak of solar wind dynamic pressure enhancement (∼14 nPa). In contrast, on the nightside, the electron density remains depleted for a longer period of time. The electron temperatures are also enhanced during the period of electron depletion on the nightside. The Suprathermal and Thermal Ion Composition (STATIC) measurements show enhanced fluxes of suprathermal heavy ions in the Martian exosphere during CIR period, and evidences for enhanced tailward flow of these pickup ions. The analysis suggests that the nightside ionosphere is primarily controlled by the precipitating Solar Energetic Particles and pickup ions transported across the Martian terminator and depletes significantly when the heavy ion flux in the exosphere enhances.

Search for water outgassing of (1) Ceres near perihelion

Context. (1) Ceres is the largest body in the main asteroid belt and one of the most intriguing objects in the solar system, in part because of the discovery of water outgassing by the Herschel Space Observatory (HSO) and its still-debated origin. Ceres was the target of NASA’s Dawn spacecraft for 3.5 yr, which achieved a detailed characterization of the dwarf planet. The possible influence of the local flux of solar energetic particles (SEP) on the production of a Cerean exosphere and water vapor has been suggested, in addition to the sublimation of water ice that depends on the temperature, meaning the heliocentric distance. Aims. We used the opportunity of both the perihelion passage of (1) Ceres in April 2018, and the presence of Dawn in its vicinity (for measuring the SEP flux in real time) to check the influence of heliocentric distance and SEP flux on water outgassing. Methods. We searched for OH emission lines near the limb of Ceres in the near-UV with the UVES spectrograph mounted on the 8-m ESO Very Large Telescope. Two spectra were recorded when Ceres was close to its perihelion, in February 2018, and with Dawn spacecraft orbiting Ceres. It was possible to simultaneously measure energetic particles around Ceres at the time of our observations. Results. Our observations did not permit detection of OH emission lines to a very high sensitivity level. This level is estimated to correspond to a global water production rate of QH2O ∽ 2 × 1026 molecules s−1, similar to the water production rate derived from HSO observations. The solar energetic particles flux measured around Ceres was negligible at the time of these observations. Conclusions. Our observations support the idea that heliocentric distance (i.e., the sublimation of water ice) does not play a major role in the water emission from Ceres. This production rate could be either related to SEP events or to other mechanisms, possibly of endogenic origin.

Acceleration of Energetic Ions in Corotating Interaction Region near 1.5 au: Evidence from MAVEN

Abstract The dearth of observations between 1 and 3 au limits our understanding of energetic particle acceleration processes in interplanetary space. We present first-of-their-kind observations of the energetic particle acceleration in a corotating interaction region (CIR) using data from two vantage points, 1 au (near Earth) and 1.5 au (near Mars). The CIR event of 2015 June was observed by the particle detectors aboard the Advanced Composition Explorer satellite as well as the Solar Energetic Particle (SEP) instrument aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft situated near 1.5 au. We find that a CIR shock can accelerate a significant number of particles even at 1.5 au. During this event the acceleration by the shocks associated with the CIR could cause an enhancement of around two orders of magnitude in the SEP energetic ion fluxes in the ∼500 keV to 2 MeV range when the observations near 1 and 1.5 au are compared. To demonstrate the differences between SEP acceleration in CIR and other impulsive events, we show the energetic ion flux observations during an intense coronal mass ejection period in March 2015, in which case the enhanced SEP fluxes are seen even at 1 au. These observations provide evidence that CIR shock can accelerate particles in the region between Earth and Mars—that is, only within the short heliocentric distance of 0.5 au—in interplanetary space.

Galactic cosmic ray hydrogen spectra and radial gradients in the inner heliosphere measured by the HELIOS Experiment 6

Context. The HELIOS solar observation probes provide unique data regarding their orbit and operation time. One of the onboard instruments, the Experiment 6 (E6), is capable of measuring ions from 4 to several hundred MeV nucleon−1. Aims. In this paper we aim to demonstrate the relevance of the E6 data for the calculation of galactic cosmic ray (GCR), anomalous cosmic ray (ACR), and solar energetic particle (SEP) fluxes for different distances from the sun and time periods. Methods. Several corrections have been applied to the raw data: determination of the Quenching factor of the scintillator, correction of the temperature dependent electronics, degradation of the scintillator as well as the effects on the edge of semi-conductor detectors. Results. Fluxes measured by the E6 are in accordance with the force field solution for the GCR and match models of the anomalous cosmic ray propagation. GCR radial gradients in the inner heliosphere show a different behaviour than in the outer heliosphere.

Connecting the Properties of Coronal Shock Waves with Those of Solar Energetic Particles

Abstract We develop and exploit a new catalog of coronal pressure waves modeled in 3D to study the potential role of these waves in accelerating solar energetic particles (SEPs) measured in situ. Our sample comprises modeled shocks and SEP events detected during solar cycle 24 observed over a broad range of longitudes. From the 3D reconstruction of shock waves using coronagraphic observations we derived the 3D velocity along the entire front as a function of time. Combining new reconstruction techniques with global models of the solar corona, we derive the 3D distribution of basic shock parameters such as Mach numbers, compression ratios, and shock geometry. We then model in a time-dependent manner how the shock wave connects magnetically with spacecraft making in situ measurements of SEPs. This allows us to compare modeled shock parameters deduced at the magnetically well-connected regions, with different key parameters of SEPs such as their maximum intensity. This approach accounts for projection effects associated with remote-sensing observations and constitutes the most extensive study to date of shock waves in the corona and their relation to SEPs. We find a high correlation between the maximum flux of SEPs and the strength of coronal shock waves quantified, for instance, by the Mach number. We discuss the implications of that work for understanding particle acceleration in the corona.

Validation of the Neutron Monitor Yield Function Using Data From AMS‐02 Experiment, 2011–2017

AbstractThe newly published spectra of protons and helium over time directly measured in space by the Alpha Magnetic Spectrometer (AMS‐02) experiment for the period 2011–2017 provide a unique opportunity to calibrate ground‐based neutron monitors (NMs). Here, calibration of several stable sea level NMs (Inuvik, Apatity, Oulu, Newark, Moscow, Hermanus, and Athens) was performed using these spectra. Four modern NM yield functions were verified: Mi13 (Mishev et al., 2013, https://doi.org/10.1002/jgra.50325), Ma16 (Mangeard et al., 2016, https://doi.org/10.1002/2016JA023515), CM12 (Caballero‐Lopez & Moraal, 2012, https://doi.org/10.1029/2012JA017794), and CD00 (Clem & Dorman, 2000, https://doi.org/10.1023/A:1026508915269), on the basis of the cosmic ray spectra measured by AMS‐02. The Mi13 yield function was found to realistically represent the NM response to galactic cosmic rays. CM12 yield function leads to a small skew in the solar cycle dependence of the scaling factor. In contrast, Ma16 and CD00 yield functions tend to overestimate the NM sensitivity to low‐rigidity (<10 GV) cosmic rays. This effect may be important for an analysis of ground level enhancements, leading to a potential underestimate of fluxes of solar energetic particles as based on NM data. The Mi13 yield function is recommended for quantitative analyses of NM data, especially for ground level enhancements. The validity of the force field approximation was studied, and it was found that it fits well the directly measured proton spectra, within a few percent for periods of low to moderate activity and up to ≈10% for active periods. The results of this work strengthen and validate the method of the cosmic ray variability analysis based on the NM data and yield function formalism and improve its accuracy.

Nowcast and forecast of galactic cosmic ray (GCR) and solar energetic particle (SEP) fluxes in magnetosphere and ionosphere – Extension of WASAVIES to Earth orbit

Real-time estimation of cosmic-ray fluxes on satellite orbits is one of the greatest challenges in space weather research. Therefore, we develop a system for nowcasting and forecasting the galactic cosmic ray (GCR) and solar energetic particle (SEP) fluxes at any location in the magnetosphere and ionosphere during ground-level enhancement (GLE) events. It is an extended version of the WArning System for AVIation Exposure to SEP (WASAVIES), which can determine event profiles by using real-time data of the count rates of several neutron monitors (NMs) at the ground level and high-energy proton fluxes observed by Geostationary Operational Environmental Satellites (GOES) satellites. The extended version, called WASAVIES-EO, can calculate the GCR and SEP fluxes outside a satellite based on its two-line element (TLE) data. Moreover, organ absorbed-dose and dose-equivalent rates of astronauts in the International Space Station (ISS) can be estimated using the system, considering its shielding effect. The accuracy of WASAVIES-EO was validated based on the dose rates measured in ISS, as well as based on high-energy proton fluxes observed by POES satellites during large GLEs that have occurred in the 21st century. Agreement between the nowcast and forecast dose rates in ISS, especially in terms of their temporal structures, indicates the usefulness of the developed system for future mission operations.

Correction Notice to: Nowcast and forecast of galactic cosmic ray (GCR) and solar energetic particle (SEP) fluxes in magnetosphere and ionosphere – Extension of WASAVIES to Earth orbit

Correction Notice to: Nowcast and forecast of galactic cosmic ray (GCR) and solar energetic particle (SEP) fluxes in magnetosphere and ionosphere – Extension of WASAVIES to Earth orbit

Early Solar System Solar Wind Implantation of 7Be into Calcium-Alumimum Rich Inclusions in Primitive Meteortites

The one time presence of short-lived radionuclides (SLRs) in Calcium-Aluminum Rich inclusions (CAIs) in primitive meteorites has been detected. The solar wind implantation model (SWIM) is one possible model that attempts to explain the catalogue of SLRs found in primitive meteorites. In the SWIM, solar energetic particle (SEP) nuclear interactions with gas in the proto-solar atmosphere of young stellar objects (YSOs) give rise to daughter nuclei, including SLRs. These daughter nuclei then may become entrained in the solar wind via magnetic field lines. Subsequently, the nuclei, including SLRs, may be implanted into CAI precursors that have fallen from the main accretion flow which had been destined for the proto-star. This mode of implanting SLRs in the solar system is viable, and is exemplified by the impregnation of the lunar surface with solar wind particles, including SLRs. X-ray luminosities have been measured to be 100,000 times more energetic in YSOs, including T-Tauri stars, than present-day solar luminosities. The SWIM scales the production rate of SLRs to nascent SEP activity in T-Tauri stars. Here, we model the implantation of 7Be into CAIs in the SWIM, utilizing the enhanced SEP fluxes and the rate of refractory mass inflowing at the X-region, 0.06 AU from the proto-Sun. Taking into account the radioactive decay of 7Be and spectral flare variations, the 7Be/9Be initial isotopic ratio is found to range from 1 × 10−5 to 5 × 10−5.

Preface to measurement, specification and forecasting of the Solar Energetic Particle (SEP) environment and Ground Level Enhancements (GLEs)

The Sun emits energetic particles following eruptive events such as solar flares and Coronal Mass Ejections (CMEs). Solar Energetic Particles (SEPs) arrive in bursts known as Solar Particle Events (SPEs), which penetrate into the Earth’s magnetosphere. SEPs with large enough energy induce a complicated atmospheric cascade, which secondary particles lead to an enhancement of count rate of ground-based detectors e.g. Neutron Monitors (NMs). This class of SEPs is therefore referred as Ground Level Enhancements (GLEs). The characterisation of the high-energy SEPs environment with corresponding space weather effects is important for space flights, aviation, and satellite industry. In this topical issue recent developments, addressing important user needs in the space radiation environment domain are published. Some articles are relevant to the specification of the SEP environment whilst others focus on space weather prediction of SEP fluxes. Catalogues based on measurement and processing of SEPs including ground-based data, and modelling of aircrew radiation exposure during major events are also presented.

Modeling solar energetic particle transport in 3D background solar wind: Influences of the compression regions

In modeling the transport process of solar energetic particles (SEPs) in the heliosphere, previous simulation works often simplify the solar wind velocity as radial and constant, and treat the magnetic field as Parker spiral. In order to fully understand the effect of solar wind velocity and interplanetary magnetic field on the particles’ transport process, a realistic background solar wind and magnetic field is required. In this work, we use the focused transport model to investigate the transport of SEPs in the solar wind velocity and magnetic field generated by the 3D high-resolution MHD model with a six-component grid. We find that in the uncompressed solar wind, the time intensity profiles of energetic particles show similar trend in both the MHD background and the Parker magnetic field assumption. However, the simulated SEP flux displays an enhancement in the decay phase when a compression region sweeps past the local observer. Through investigating various effects, we find that the magnetic focusing effect is primarily responsible for the intensity enhancement, suggesting that the magnetic focusing effect has an important influence on the transport of SEPs. Further, we show that the magnetic focusing could also be effective in large heliocentric distances.

Solar energetic particles and galactic cosmic rays over millions of years as inferred from data on cosmogenic26Al in lunar samples

Aims.Lunar soil and rocks are not protected by a magnetic field or an atmosphere and are continuously irradiated by energetic particles that can produce cosmogenic radioisotopes directly inside rocks at different depths depending on the particle’s energy. This allows the mean fluxes of solar and galactic cosmic rays to be assessed on the very long timescales of millions of years.Methods.Here we show that lunar rocks can serve as a very good particle integral spectrometer in the energy range 20–80 MeV. We have developed a new method based on precise modeling, that is applied to measurements of26Al (half-life ≈0.7 megayears) in lunar samples from theApollomission, and present the first direct reconstruction (i.e., without any a priori assumptions) of the mean energy spectrum of solar and galactic energetic particles over a million of years.Results.We show that the reconstructed spectrum of solar energetic particles is totally consistent with that over the last decades, despite the very different levels of solar modulation of galactic cosmic rays (ϕ= 496 ± 40 MV over a million years versus (ϕ= 660 ± 20 MV for the modern epoch). We also estimated the occurrence probability of extreme solar events and argue that no events with theF(>30 MeV) fluence exceeding 5×1010and 1011cm−2are expected on timescales of a thousand and million years, respectively.Conclusions.We conclude that the mean flux of solar energetic particles hardly depends on the level of solar activity, in contrast to the solar modulation of galactic cosmic rays. This puts new observational constraints on solar physics and becomes important for assessing radiation hazards for the planned space missions.

Bare Neutron Counter and Neutron Monitor Response to Cosmic Rays During a 1995 Latitude Survey

AbstractNeutron monitors of standard design (IGY or NM64) are employed worldwide to study variations in the flux of galactic cosmic rays and solar energetic particles in the GeV range. The design minimizes detector response to neutrons below ∼10 MeV produced by cosmic ray interactions in the ambient medium. Increasingly, however, such neutrons are of interest as a means of obtaining spectral information on cosmic rays, for studies of soil moisture, and for nuclear threat detection. Bare neutron counters, a type of lead‐free neutron monitor, can detect such neutrons, but comparatively little work has been done to characterize the dependence of their count rate on cutoff rigidity. We analyze data from three bare neutron counters operated on a ship together with a three‐tube NM64 monitor from November 1995 to March 1996 over a wide range of magnetic latitude, that is, a latitude survey. The bare counter design used foamed‐in‐place polyurethane insulation to keep the temperature uniform and to some extent moderate high‐energy neutrons. When the ship was near land, the bare/NM64 count rate ratio was dramatically higher. Considering only data from open sea, the bare and NM64 pressure coefficients are not significantly different. We determine the response function of these bare counters, which is weighted to Galactic cosmic rays of lower energy than the NM64. This measurement of the response function may improve determination of the spectral index of solar energetic particles and Galactic cosmic rays from a comparison of bare and NM64 count rates.

Comparative analysis of the proton generation efficiency during 17 March 2003 and 11 April 2004 solar flares

We present the comparative analysis of the solar energetic particle (SEP) event properties and the indicators of acceleration processes in solar flares − the hard X-rays (HXR) and radio emission from microwaves to the meter-range. We focus our study on the two SEP events associated with solar flares with similar characteristics in HXR emission and the close location on solar disk. The proton flux in the SEP event associated with the weaker flare by GOES class in soft X-ray (SXR) (C9.6/SOL2004-Apr-11) was more than an order higher than in the SEP event associated with the more powerful solar flare (X1.5/SOL2003-Mar-17). At the same time, the electron fluxes in both SEP events were comparable. Both flares were followed by CMEs with speed above 1000 km s−1. The analysis of SEP fluxes and flare plasma parameters was done taking into account the magnetic topology of the active region (AR) and its evolution before and during the solar flares. The 3D reconstruction of the potential magnetic field showed the existence of an arcade of high loops covering the active region where the more powerful flare occurred. The flare associated with the proton-rich SEP event occurred in the active region where 3D reconstruction revealed a fan of high loops associated with open magnetic field lines. We suppose that the arcade of high loops could be the factor which prevents an escape of the accelerated particles into the interplanetary space (IPS) while the fan of high loops facilitates the production of the more proton-rich SEP events. Results of the analysis show a necessity to use topology of ARs as a parameter in statistical studies of SEP event origins.