Ground Level Enhancement Research Articles

Ionization effect in the Earth’s atmosphere due to cosmic rays during the GLE [formula omitted] 71 on 17 May 2012

Nowadays the systematic study of the possible effect of precipitating high-energy particles on atmospheric physics and chemistry is in great expansion. Most of the recent models studying the precipitating energetic particles effects in the Earth’s atmosphere are based on reliable quantification of the induced ionization, that is, the cosmic ray impact ionization, which is extensively studied over the last decade. While the galactic cosmic rays are the main source of ionization in the Earth’s stratosphere and troposphere, the energetic particles of solar origin can significantly enhance the ion production following strong solar eruptions, specifically over the polar caps. A particular interest represents solar protons observed by ground-based detectors, viz. the so-called ground level enhancements (GLE), observed as an increase of the count rate of e.g. neutron monitors. Here, employing 3-D Monte Carlo model, we computed the solar protons induced atmospheric ionization during the moderate GLE # 71 on 17 May 2012. The ion production rates were computed during various stages of the event as a function of the altitude above sea level using derived by verified model particles spectra. The 24 h averaged ionization effect relative to the average due to the galactic cosmic rays was computed at several depths in the atmosphere.

Global planetary ionization maps in Regener-Pfotzer cosmic ray maximum for GLE 66 during magnetic superstorm of 29–31 October 2003

High-energy particles of cosmic origin e.g. cosmic ray protons and heavier nuclei of galactic and/or solar origin induce complicated nuclear-electromagnetic-meson cascades in the Earth’s atmosphere, eventually leading to an ionization of the ambient air. The induced by cosmic rays atmospheric ionization is related to possible effect of precipitating particles on atmospheric physics and chemistry. These effects can be considerably enhanced during strong and moderately strong solar proton events. While the contribution of galactic cosmic ray particles to ion production in the atmosphere is slightly variable throughout a solar cycle, relativistic solar particles could produce a significant excess on ion pair production, particularly over polar caps. This effect is strong on a short time scales. On the other hand, depressions of the galactic cosmic ray flux, that is, Forbush decreases, can significantly impact the galactic cosmic ray induced ionization. The sequence of three ground level enhancements observed in October-November 2003, specifically the second: GLE 66 which occurred during a giant Forbush decrease, provides unique opportunity to study impact ionization on extended time scale, explicitly considering the reduced galactic cosmic ray flux. Using Monte Carlo simulations we computed the ion production rate and the corresponding ionization effect in the Earth atmosphere during GLE 66 occurred on 29 October 2003, explicitly considering the Forbush decrease and the complex geomagnetospheric conditions.

Testing the simultaneity of Forbush decreases with algorithm-selected Forbush event catalogue

Accurate detection and precise timing of transient events such as X-ray photons, $$\gamma $$ -ray burst, coronal mass ejections (CMEs), ground-level enhancements (GLEs) and Forbush decreases (FDs) frequently raise issues that remain on the cutting edge of research in astrophysics. In an attempt to automate FD event selection, a combination of Fast Fourier transform as well as FD detection algorithms implemented in the statistical computing software R was developed and recently used to calculate the magnitude and FD event timing. The R-FD code implemented in the present study includes several different calculations. Some subroutines detect both small and large transient intensity reductions (minima/pits) as well as increases (maxima/peaks) in cosmic ray (CR) data. Others calculate event amplitude, timing and cataloguing of the events identified. As the current work focuses on reductions in CR flux (FDs), the subroutine that identifies increases was disabled. Totals of 229 FDs at Magadan neutron monitor (NM), 230 (Oulu NM) and 224 (Inuvick NM) were identified with daily averaged data, while 4032 (Magadan), 4144 (Oulu) and 4055 (Inuvick) were detected with hourly averages. FDs identified as simultaneous at the three stations totaled 99 for the daily and 261 for the hourly CR averages respectively.

Fluences of solar energetic particles for last three GLE events: Comparison of different reconstruction methods

Fluxes of solar energetic particles (SEPs), produced and accelerated in and in the vicinity of the Sun, are an important part of cosmic ray induced terrestrial effects such as ionizing radiation on the Earth’s orbit, which affects the exposure to radiation in space as well as the atmospheric ionization. Calculation of these effects requires the knowledge of the integral fluences of SEPs. High-energy solar particles are subject of special interest since they can significantly contribute to the total radiation dose and/or ionization. The main instrument to study the high-energy SEP events is a network of ground-based neutron monitors (NMs), used over the years to register a specific class of SEP, which is called ground-level enhancement (GLE) events. Up today, we possess records from 72 GLE events. Reconstruction of SEP integral and differential fluxes for GLE events using NM data is not an easy task, requires a careful and precise calculation of particle transport in the magnetosphere, atmosphere, and detector itself. In this work, we compare two methods of fluence reconstruction, “fast” and “full”, for the last three registered GLE events and additionally verify one of them using PAMELA experimental data.

Analysis of the solar cosmic-ray spectrum during ground-level enhancements

In this work, we analyze the spectrum of solar cosmic rays flux during ground-level enhancements using the pair of lead-free and standard neutron monitors in the South Pole station. Using both monitor data, effects due to anisotropy are considerably reduced. We assume a power-law form for the solar particle spectrum at the top of the atmosphere. The spectral index was computed during all events for which data were available, regardless of the duration or the intensity of the GLE. Seventeen events were analyzed. In this paper, we show the efficiency of the method used, as well as a clear tendency of the spectral index behavior to the ratio between the observed increases in both monitors. It is also shown that the method can be used to calculate the solar cosmic ray spectrum at any required stage of the event. Our results show that the spectral index estimation depends on the choice of the yield function. For the three yield functions used in the analysis, the spectral index changes by about 10%.

Calibration of the GOES 6–16 high-energy proton detectors based on modelling of ground level enhancement energy spectra

For several decades, the Geostationary Operational Environmental Satellites (GOES) series have provided both real-time and historical data for radiation exposure estimation and solar proton radiation environment modelling. Recently, several groups conducted calibration studies that significantly reduced the uncertainties on the response of GOES proton detectors, thus improving the reliability of the spectral observations of solar energetic particle events. In this work, the long-established Band function fitting set for past ground level enhancements (GLEs) and their recent revision are used as references to estimate the best matching energies of proton channels of GOES 6–16, with emphasis on comparing with previous calibration studies on the high energetic proton measurements. The calculated energies for different missions in the same series (GOES 8, 10, 11) show overall consistency but with small variations, and differences among missions of different series are noticeable for measurements crossing the past three solar cycles, though the results are sensitive to the method used to subtract background fluxes. The discrepancy and agreement with previous calibration efforts are demonstrated with other independent analyses. It is verified that the integral channel P11 of GOES 6–16 can be reliably used as a differential proton channel with an effective energy of about 1 GeV. Therefore, the multi-decade in situ measurements of the GOES series can be utilized with more extensive energy coverage to improve space radiation environment models.

Shock Properties and Associated Characteristics of Solar Energetic Particles in the 2017 September 10 Ground-level Enhancement Event

Abstract The solar eruption on 2017 September 10 was accompanied by a fast coronal mass ejection (∼3000 km s−1) and produced a ground-level enhancement (GLE) event at Earth. Multiple-viewpoint remote sensing observations are used to find the three-dimensional (3D) structure of the shock. We determine the shock parameters by combining the 3D shock kinematics and the solar wind properties obtained from a global magnetohydrodynamic (MHD) simulation, in order to compare them with the characteristics of the solar energetic particles (SEPs). We extract the magnetic connectivities of the observers from the MHD simulation and find that L1 was magnetically connected to the shock flank (rather than the nose). Further analysis shows that this shock flank propagates through the heliospheric current sheet (HCS). The weak magnetic field and relatively dense plasma around the HCS result in a large Mach number of the shock, which leads to efficient particle acceleration even at the shock flank. We conclude that the interaction between the shock and HCS provides a potential mechanism for production of the GLE event. The comparison between the shock properties and the characteristics of SEPs suggests an efficient particle acceleration in a wide spatial range by the shock propagating through the highly inhomogeneous coronal medium.

Probabilistic risk assessment of solar particle events considering the cost of countermeasures to reduce the aviation radiation dose

Cosmic-ray exposure to flight crews and passengers, which is called aviation radiation exposure, is an important topic in radiological protection, particularly for solar energetic particles (SEP). We therefore assessed the risks associated with the countermeasure costs to reduce SEP doses and dose rates for eight flight routes during five ground level enhancements (GLE). A four-dimensional dose-rate database developed by the Warning System for Aviation Exposure to Solar Energetic Particles, WASAVIES, was employed in the SEP dose evaluation. As for the cost estimation, we considered two countermeasures; one is the cancellation of the flight, and the other is the reduction of flight altitudes. Then, we estimated the annual occurrence frequency of significant GLE events that would bring the maximum flight route dose and dose rate over 1.0 mSv and 80 μSv/h, respectively, based on past records of GLE as well as historically large events observed by the cosmogenic nuclide concentrations in tree rings and ice cores. Our calculations suggest that GLE events of a magnitude sufficient to exceed the above dose and dose rate thresholds, requiring a change in flight conditions, occur once every 47 and 17 years, respectively, and their conservatively-estimated annual risks associated with the countermeasure costs are up to around 1.5 thousand USD in the cases of daily-operated long-distance flights.

Ground-Level Enhancement in the Intensity of Cosmic Rays during the Decay Phase of Solar Cycle 24: Spectra and Anisotropy

Ground-Level Enhancement in the Intensity of Cosmic Rays during the Decay Phase of Solar Cycle 24: Spectra and Anisotropy

The Common Origin of High-energy Protons in Solar Energetic Particle Events and Sustained Gamma-Ray Emission from the Sun

Abstract We report that the number of >500 MeV protons (Ng ) inferred from sustained gamma-ray emission (SGRE) from the Sun is significantly correlated with that of protons propagating into space (N SEP) as solar energetic particles (SEPs). Under the shock paradigm for SGRE, shocks driven by coronal mass ejections (CMEs) accelerate high-energy protons sending them toward the Sun to produce SGRE by interacting with the atmospheric particles. Particles also escape into the space away from the Sun to be detected as SEP events. Therefore, the significant N SEP–N g correlation (correlation coefficient 0.77) is consistent with the common shock origin for the two proton populations. Furthermore, the underlying CMEs have properties akin to those involved in ground level enhancement events indicating the presence of high-energy (up to ∼GeV) particles required for SGRE. We show that the observed gamma-ray flux is an underestimate in limb events (central meridian distance >60°) because SGRE sources are partially occulted when the emission is spatially extended. With the assumption that the SEP spectrum at the shock nose is hard and that the 100 MeV particles are accelerated throughout the shock surface (half width in the range 60°–120°) we find that the latitudinal widths of SEP distributions are energy dependent with the smallest width at the highest energies. Not using the energy-dependent width results in an underestimate of N SEP in SGRE events occurring at relatively higher latitudes. Taking these two effects into account removes the apparent lack of N SEP–N g correlation reported in previous studies.

Ground level enhancements of cosmic rays on October–November 2003

We study variations in the rigidity spectrum and anisotropy of cosmic rays (CRs) by using the data from satellite and ground-based observations within the worldwide network of cosmic-ray detectors through the global spectrographic survey. The studied period covers 28 and 29 October and 2 November 2003 (GLE65, GLE66, and GLE67). We determined CR differential rigidity spectra at individual hours of the investigated events. The maximal rigidity of accelerated protons in these GLEs is shown to equal ~ 4–14 GV.

Extreme space weather events caused by super active regions during solar cycles 21-24

Extreme space weather events including ≥X5.0 flares, ground level enhancement (GLE) events and super geomagnetic storms (Dst ≤ –250 nT) caused by super active regions (SARs) during solar cycles 21–24 were studied. The total number of ≥X5.0 solar flares was 62, among which 41 were X5.0-X9.9 flares and 21 were ≥X10.0 flares. We found that 83.9% of the ≥X5.0 flares were produced by SARs; 78.05% of the X5.0-X9.9 and 95.24% of the ≥X10.0 solar flares were produced by SARs; 46 GLEs were registered during solar cycles 21–24, and 25 GLEs were caused by SARs, indicating that 54.3% of the GLEs were caused by SARs; 24 super geomagnetic storms were recorded during solar cycles 21–24, and 12 of them were caused by SARs, namely 50% of the super geomagnetic storms were caused by SARs. We ascertained that only 29 SARs produced ≥X5.0 flares, 15 SARs generated GLEs and 10 SARs triggered super geomagnetic storms. Of the 51 SARs, only 33 SARs produced at least one extreme space weather event, while none of the other 18 SARs could trigger an extreme space weather event. There were only four SARs and each of them generated not only a ≥X5.0 flare, but also a GLE event and a super geomagnetic storm. Most of the extreme space weather events caused by the SARs appeared during solar cycles 22 and 23, especially for GLE events and super geomagnetic storms. The longitudinal distributions of source locations for the extreme space weather events caused by SARs were also studied.

GLE # 67 Event on 2 November 2003: An Analysis of the Spectral and Anisotropy Characteristics Using Verified Yield Function and Detrended Neutron Monitor Data

During Solar Cycle 23 16 ground-level enhancement events were registered by the global neutron monitor network. In this work we focus on the period with increased solar activity during late October – early November 2003 producing a sequence of three events, specifically on ground-level enhancement GLE 67 on 2 November 2003. On the basis of an analysis of neutron monitor and space-borne data we derived the spectra and pitch-angle distribution of high-energy solar particles with their dynamical evolution throughout the event. According to our analysis, the best fit of the spectral and angular properties of solar particles was obtained by a modified power-law rigidity spectrum and a double Gaussian, respectively. The derived angular distribution is consistent with the observations where an early count rate increase at Oulu neutron monitor with asymptotic viewing direction in the anti-Sun direction was registered. The quality of the fit and model constraints were assessed by a forward modeling. The event integrated particle fluence was derived using two different methods. The derived results are briefly discussed.

Study of the Impact of Past Extreme Solar Events on the Modern Air Traffic

AbstractThe ancient solar energetic particle (SEP) events of 774/775 CE and 993/994 CE were characterized thanks to radionuclide productions stored in environmental archives as ice cores or tree rings. Primary cosmic ray spectra deduced from these cosmogenic isotope data indicate that the impact of these extreme SEP events would have been much more significant than any of the ones observed during the modern era. However, the impact of these should be studied more accurately in the framework of the ambient dose equivalent impacting aircrew and passengers in the air traffic context by considering physical parameters such as time profile or anisotropy properties. In this study, the impact that 774/775 CE and 993/994 CE past extreme SEP events could have had on modern air traffic is discussed. Possible event spectra for these ancient events are derived from the spectra ground‐level enhancement (GLE) 5 and GLE 69, which have been observed during the modern era and have been widely studied/characterized using measurements. The investigations include the impact of the SEP activity on ambient dose equivalent, including detailed analyses considering route, airplane characteristics (departure, arrival, continent, airplane type), and the time occurrence of the SEP event. Statistical analyses show that additional dose levels can reach values on the order of 70 mSv, which is absolutely significant considering the current air traffic recommendations. The orders of magnitude of the ambient dose equivalent induced during past extreme SEP events raises a number of issues, both for aircrews and for avionics hardware. This study demonstrates that simulations can be useful for the evaluation of risks in case of extreme SEP events.

Solar activity and Earth seismicity

Using the results of continuous long-term observations over 50 years (including solar cycles 20–24), we study the relationship between Earth’s seismicity and solar activity. An increase in the number of strong earthquakes on the planet occurs during the decline phase of solar activity when charged particle fluxes from high-latitude coronal holes increase, as well as during solar minimum when the intensity of galactic cosmic rays reaches a maximum. The change in the number of strong earthquakes (with magnitude 6) is considered in terms of variations in the intensity of galactic cosmic rays, Forbush decreases, and ground level enhancements in solar cosmic rays (GLE events). The number of strong earthquakes is shown to increase after Forbush decreases with a time lag from ~1 to ~6 days depending on the amplitude of Forbush decrease and after GLE events the number of strong earthquakes increases by ~8 day. In the number of strong earthquakes, a six-month variation is observed, which seems to follow the six-month variation in cosmic rays with a delay of ~1–2 months. It is surmised that the relationship between solar activity and Earth’s seismicity seems to be mediated through the modulation of galactic cosmic rays and atmospheric processes that provoke the occurrence of earthquakes in regions where the situation has already been prepared by tectonic activity.

Солнечная активность и сейсмичность Земли

Using the results of continuous long-term observations over 50 years (including solar cycles 20–24), we study the relationship between Earth’s seismicity and solar activity. An increase in the number of strong earthquakes on the planet occurs during the decline phase of solar activity when charged particle fluxes from high-latitude coronal holes increase, as well as during solar minimum when the intensity of galactic cosmic rays reaches a maximum. The change in the number of strong earthquakes (with magnitude 6) is considered in terms of variations in the intensity of galactic cosmic rays, Forbush decreases, and ground level enhancements in solar cosmic rays (GLE events). The number of strong earthquakes is shown to increase after Forbush decreases with a time lag from ~1 to ~6 days depending on the amplitude of Forbush decrease and after GLE events the number of strong earthquakes increases by ~8 day. In the number of strong earthquakes, a six-month variation is observed, which seems to follow the six-month variation in cosmic rays with a delay of ~1–2 months. It is surmised that the relationship between solar activity and Earth’s seismicity seems to be mediated through the modulation of galactic cosmic rays and atmospheric processes that provoke the occurrence of earthquakes in regions where the situation has already been prepared by tectonic activity.

The Intensity and Evolution of the Extreme Solar and Geomagnetic Storms in 1938 January

Abstract Major solar eruptions occasionally direct interplanetary coronal mass ejections (ICMEs) to Earth and cause significant geomagnetic storms and low-latitude aurorae. While individual extreme storms are significant threats to modern civilization, storms occasionally appear in sequence, acting synergistically, and cause “perfect storms” on Earth. The stormy interval in 1938 January was one of such cases. Here, we analyze the contemporary records to reveal its time series on their source active regions, solar eruptions, ICMEs, geomagnetic storms, low-latitude aurorae, and cosmic-ray (CR) variations. Geomagnetic records show that three storms occurred successively on January 17/18 (Dcx ≈ −171 nT), January 21/22 (Dcx ≈ −328 nT), and January 25/26 (Dcx ≈ −336 nT). The amplitudes of the CR variations and storm sudden commencements (SSCs) show the impact of the first ICME as the largest (≈6% decrease in CR and 72 nT in SSC) and the ICMEs associated with the storms that followed as more moderate (≈3% decrease in CR and 63 nT in SSC; ≈2% decrease in CR and 63 nT in SSC). Interestingly, a significant solar proton event occurred on January 16/17 and the Cheltenham ionization chamber showed a possible ground-level enhancement. During the first storm, aurorae were less visible at midlatitudes, whereas, during the second and third storms, the equatorward boundaries of the auroral oval were extended down to 40.3° and 40.0° in invariant latitude. This contrast shows that the initial ICME was probably faster, with a higher total magnitude but a smaller southward component.

New reconstruction of event-integrated spectra (spectral fluences) for major solar energetic particle events

Aims. Fluences of solar energetic particles (SEPs) are not easy to evaluate, especially for high-energy events (i.e. ground-level enhancements, GLEs). Earlier estimates of event-integrated SEP fluences for GLEs were based on partly outdated assumptions and data, and they required revisions. Here, we present the results of a full revision of the spectral fluences for most major SEP events (GLEs) for the period from 1956 to 2017 using updated low-energy flux estimates along with greatly revisited high-energy flux data and applying the newly invented reconstruction method including an improved neutron-monitor yield function. Methods. Low- and high-energy parts of the SEP fluence were estimated using a revised space-borne/ionospheric data and ground-based neutron monitors, respectively. The measured data were fitted by the modified Band function spectral shape. The best-fit parameters and their uncertainties were assessed using a direct Monte Carlo method. Results. A full reconstruction of the event-integrated spectral fluences was performed in the energy range above 30 MeV, parametrised and tabulated for easy use along with estimates of the 68% confidence intervals. Conclusions. This forms a solid basis for more precise studies of the physics of solar eruptive events and the transport of energetic particles in the interplanetary medium, as well as the related applications.

Energetic Proton Propagation and Acceleration Simulated for the Bastille Day Event of 2000 July 14

Abstract This work presents results from simulations of the 2000 July 14 (“Bastille Day”) solar proton event. We used the Energetic Particle Radiation Environment Model (EPREM) and the CORona-HELiosphere (CORHEL) software suite within the SPE Threat Assessment Tool (STAT) framework to model proton acceleration to GeV energies due to the passage of a CME through the low solar corona, and we compared the model results to GOES-08 observations. The coupled simulation models particle acceleration from 1 to 20 R ⊙, after which it models only particle transport. The simulation roughly reproduces the peak event fluxes and the timing and spatial location of the energetic particle event. While peak fluxes and overall variation within the first few hours of the simulation agree well with observations, the modeled CME moves beyond the inner simulation boundary after several hours. The model therefore accurately describes the acceleration processes in the low corona and resolves the sites of most rapid acceleration close to the Sun. Plots of integral flux envelopes from multiple simulated observers near Earth further improve the comparison to observations and increase potential for predicting solar particle events. Broken power-law fits to fluence spectra agree with diffusive acceleration theory over the low energy range. Over the high energy range, they demonstrate the variability in acceleration rate and mirror the interevent variability observed in solar cycle 23 ground-level enhancements. We discuss ways to improve STAT predictions, including using corrected GOES energy bins and computing fits to the seed spectrum. This paper demonstrates a predictive tool for simulating low-coronal solar energetic particle acceleration.

Application of the Verified Neutron Monitor Yield Function for an Extended Analysis of the GLE # 71 on 17 May 2012

AbstractIntense solar activity was observed in May 2012. A notable ground level enhancement (GLE) was registered on 17 May 2012 by several space‐borne instruments as well as on ground by neutron monitors (NMs). This event is known as GLE # 71. Here, we derived the spectral and angular characteristics, and apparent source position of the solar protons during the GLE # 71, employing verified newly computed NM yield function and sophisticated unfolding procedure. We considerably improved the previously derived information about the spectra and angular distribution, namely, the precision, time span, and time resolution of the derived characteristics, specifically during the event onset and late phase. A comparison with direct measurements, with the Payload for Antimatter Matter Exploration and Light‐nuclei Astrophysics (PAMELA) experiment, of the particle fluence was performed, and good agreement between NM and direct space‐borne data analysis was achieved. Subsequently, we computed the effective dose rates in the polar region at several altitudes during the event using the derived rigidity spectra of the solar protons as a reliable input for the corresponding radiation model. The contribution of the galactic cosmic rays and solar protons to the exposure is explicitly considered. We computed the integrated exposure during the event and discussed the exposure of crew members/passengers to radiation at several altitudes.