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In association with the X28 solar flare on November 4, 2003, the muon telescope installed in Mexico City observed an enhancement in its counting rate between 19:55 and 20:00 UT. Based on a numerical simulation, we found that the entry of a high-energy solar neutron, with energy range from 0.2 to 2 GeV, is capable of producing muon flux that reach the atmospheric depth of Mexico City. Furthermore, we also found that this muon flux is of the order of 3% with respect to the average muon flux recorded by the telescope. Therefore it is very likely that the excess signals observed in the muon telescope are due to muons generated by solar neutrons in the Earth's atmosphere. [ABSTRACT FROM AUTHOR]

Solar Cycle 23 was the most active in ground-level enhancements (GLEs) with 16 events registered by the global neutron monitor network. In this paper, we study a very active period in October–November, 2003, which revealed an intense solar activity burst that led to several eruptive processes and produced a sequence of three GLEs. By applying state-of-the-art modelling to records from the global neutron monitor network as well as space-borne data, we derived the spectral and anisotropy characteristics of accelerated solar protons during the GLE #65 event on 28 October, 2003 and GLE #66 on 29 October, 2003. The spectra and the pitch angle distributions are obtained with a 5-min time resolution, providing their dynamical evolution throughout the event. The spectra are parameterised with a modified power-law rigidity spectrum, whilst the angular distribution with a Gaussian. The constraints and uncertainties of the derived characteristics are evaluated by corresponding modelling. [ABSTRACT FROM AUTHOR]

Intense solar energetic particle (SEP) events can be observed by neutron monitors (NMs) as so-called ground-level enhancements (GLEs). High-altitude polar NMs have high sensitivity for SEP due to the reduced atmospheric energy cutoff and very low geomagnetic rigidity cutoff compared to other NMs. There is a special class of sub-GLE events, viz. events that are weaker than standard GLEs and can only be observed by high-altitude polar NMs. So far, only one sub-GLE and three candidates are known, all in the period 2012 – 2015. In this work, we inspected the period from March 1964 to December 1969 in the data of the South Pole and Vostok high-altitude polar NMs on the Antarctic Plateau in search of possible sub-GLEs. We found two previously unknown events from 09 June 1968 and 27 February 1969 that formally match the definition of sub-GLE. They were associated with significant enhancements in the integral SEP intensity J (> 60 MeV) measured by space-borne particle detectors, as well as with strong X-class solar flares from the western part of the solar disk. The identified sub-GLEs were analyzed and the corresponding SEP characteristics were estimated. [ABSTRACT FROM AUTHOR]

We discuss a newly established neutron monitor station installed at the ENTOTO Observatory Research Center outside of Addis Ababa, Ethiopia. This is a version of a mini-neutron monitor, recently upgraded to detect individual neutrons and able to calculate the waiting time distribution between neutron pulses down to ∼ 1 μ s. From the waiting time distribution we define and calculate a new quantity, the correlation ratio, as the ratio of correlated to uncorrelated neutrons measured inside the monitor. We propose that this quantity can, in future, be used as a proxy for spectral index of atmospheric particles incident on the monitor and show that this quantity has a weak pressure dependence. We believe that future measurements from the ENTOTO mini-neutron monitor will contribute towards the understanding of cosmic ray acceleration and transport in the heliosphere. [ABSTRACT FROM AUTHOR]

Abstract The European Spallation Source ERIC (ESS), currently under construction in Lund, Sweden is a facility established to deliver the highest integrated neutron flux originating from a pulsed source with the aim of supporting an initial fifteen neutron instruments for cutting edge science experiments. This in turn requires reliable monitoring at complex neutron beam lines: in particular, linearity, timing capability, adaptability of the design for various flux ranges (dynamic range) and sensitivity to neutrons within the range of 0.6-10Å are expected from the neutron beam monitors to be installed at the ESS beam lines. Additionally, operational stability and low attenuation are also desirable characteristics for such neutron beam monitoring. A prototype neutron beam monitor based on the ionisation chamber principle and a boron converter, designed by CDT CASCADE Detector Technologies GmbH and ESS, has been investigated at the BER-II research reactor of Helmholtz Zentrum Berlin (HZB). The effort to design and investigate a thermal neutron ionisation beam monitor was initiated by adapting the concept of ionisation chambers previously known elsewhere. So far all the characterised neutron beam monitors discriminate neutron hits on a discrete event basis (pulse mode), whereas the beam monitor prototype introduced in this paper estimates the total flux as a function of current (current mode). While most other neutron beam monitoring devices and detectors rely upon a signal amplifying gain stage, the ionisation chamber operates without any gain and is consequently robust against typical detector ageing effects that compromise the sensitivity over time. The initial tests were performed at the ESS V20 test beam line under realistic conditions resembling those of the future pulses of ESS. The linearity is demonstrated for 3Å pulses in the flux range of 2-3 × 105 n/s/cm2 and for white pulses (0.6-10Å) in the range of 1-5 × 106 n/s/cm2. The timing behaviour resembles the data previously recorded at the V20 beam lines. This novel implementation of a neutron sensitive ionisation chamber shows great promise for beam monitoring and diagnostics at ESS. As the ionisation beam monitor itself is an entirely passive device, it is adequately robust to be employed in areas of high irradiation where no regular servicing or maintenance can be provided.

Galactic cosmic rays (GCRs) impinge on the Earth's atmosphere and generate showers of secondary particles in nuclear collisions with the atmospheric constituents. The flux of GCR near Earth is subjected to heliospheric modulation driven by solar magnetic activity and to geomagnetic shielding. Variability of the GCR flux is continuously monitored by the worldwide network of ground‐based neutron monitors (NMs) since the 1950s. Solar modulation is often quantified via the force‐field approximation parameterized by the modulation potential ϕ, which can be evaluated from the global NM data set. Here we revisit the methodology and provide an updated and extended reconstruction of the heliospheric modulation potential for 1964–2022, using a recent NM yield function and the measurements of the 10 most stable high‐latitude NMs. A key improvement in the reconstructed heliospheric modulation potential is the new daily resolution, which provides new opportunities for further research. Reconstruction uses the root‐mean square error (RMSE) minimization to find the optimum daily and monthly scaling factors for individual NMs. The stability of the reconstruction is analyzed and the errors are estimated. The mean level of uncertainty is low, generally within ±1%, but it is found to depict marginal variability at the 11‐year, annual and 27‐day timescales at the <1% level, indicating that a very small systematic uncertainty is still present.Key Points: An updated reconstruction of the monthly heliospheric modulation potential is derived for 1964–2022A new unique daily‐resolution version of the heliospheric modulation potential is presentedThe stability of individual neutron monitors is assessed for 1964–2022 [ABSTRACT FROM AUTHOR]

Cosmic‐ray neutron sensors (CRNS) have been used in many studies for measuring soil moisture and snow pack over intermediate scales. Corrections for barometric pressure and atmospheric humidity are well established, however, corrections for the effect of solar activity on neutron intensity rates have been overly simplistic, typically relying on one neutron monitor station and accounting for latitude and elevation crudely or not at all. Recognizing the lack of a generalized and scientifically robust approach to neutron intensity correction, we developed a new approach for correcting CRNS count rates based on analysis of data from 110 quality‐controlled neutron monitor stations from around the world spanning more than seven decades. Count rates from each monitor were plotted against the count rates from Climax, CO, USA or Jungfraujoch, Switzerland depending on the time period covered. Relationships between relative counting rates at the site of interest versus the reference neutron monitors were found to be strongly linear. The slope and intercept of these linear relation are both dependent on a scaling factor referred to as τ $\tau $, which was shown to increase with increasing geomagnetic latitude and elevation. This dependence was represented using an empirical relationship based on a single reference neutron monitor. This generalized approach enables τ $\tau $ to be derived for any location on Earth and also lends itself to roving CRNS studies. The correction procedure also includes a location‐dependent normalization factor which enables easy substitution of an alternative reference neutron monitor into the correction procedure. Plain Language Summary: Cosmic‐ray neutron sensors (CRNS) are used for measuring soil moisture and snow pack at the scale of hectares. Corrections to account for changes in atmospheric pressure and humidity on CRNS measurements are well established and widely applied, however, corrections for changes in incoming cosmic‐ray neutron intensity because of solar activity have been overly simplistic. We developed a new approach for correcting CRNS count rates based on analysis of data from 110 neutron monitor stations from around the world with datasets spanning more than seven decades. A strong relationship was found between the relative count rate of neutron monitors from around the world, with the magnitude of the correction increasing toward the poles and with elevation. The relationship we found can be applied at any CRNS location based on its elevation, latitude, and longitude to correct for changes to incoming cosmic‐ray neutron intensity. Key Points: A new approach for correcting cosmic ray neutron sensor data for the effects of fluctuating intensities of incoming neutrons is presentedThe approach is based on analysis of data from 110 neutron monitor stations from around the world with data spanning more than seven decadesThe approach can be applied at any location on Earth and includes the ability to utilize any neutron monitor as a reference station [ABSTRACT FROM AUTHOR]

The impact of solar wind plasma on fluxes of galactic cosmic rays (CR) penetrating from the outside into the heliosphere with energies above ~1 GeV leads to temporal variations in the CR intensity in a wide frequency range. Cosmic rays being charged particles, their modulation occurs mainly under impacts of the interplanetary magnetic field. It is well known that the observed spectrum of interplanetary magnetic field (IMF) fluctuations in a wide frequency range ν from ~10–7 to ~10 Hz has a pronounced falling character and consists of three sections: energy, inertial, and dissipative. Each of them is described by the power law PIMF(ν)~ν–α, while the IMF spectrum index α increases with increasing frequency. The IMF fluctuations in each of these sections are also characterized by properties that depend on their nature. Also known are established links between fluctuation spectra of the interplanetary magnetic field and galactic cosmic rays in the case of modulation of the latter by Alfvén or fast magnetosonic waves. The theory predicts that fluctuation spectra of cosmic rays should also be described by the power law PCR(ν)~ν–γ. However, the results of many years of SHICRA SB RAS research into the nature and properties of cosmic ray intensity fluctuations based on data from neutron monitors at stations with different geomagnetic cut-offs RC from 0.5 to 6.3 GV show that the observed spectrum of fluctuations in galactic cosmic ray intensity in the frequency range above 10–4 Hz becomes flat, i.e. it is similar to white noise. This fact needs to be realized and explained. This paper reports the results of research into the shape of the spectrum of galactic cosmic ray intensity fluctuations within a frequency range ν from ~10–6 to ~1 Hz and compares them with model calculations of white noise spectra, using measurement data from the neutron monitor of the Apatity station. A possible physical explanation has been given for the observed shape of the cosmic ray fluctuation spectrum on the basis of the known mechanisms of their modulation in the heliosphere.

The Forbush effect is one of the striking examples of irregular variations in the cosmic ray (CR) flux. It is a heliospheric phenomenon that includes a decrease and a recovery of the CR intensity and small changes in the CR density and anisotropy before the start of the main decrease. They were first noted as the effects of decreasing the intensity of cosmic rays, coinciding with geomagnetic storms. The increased interest is observed in recent years and it is primarily because their variables are strongly related to processes in solar-terrestrial physics. Forbush effects convey significant information regarding interplanetary disturbances. In the present work, fifty-three Forbush decrease (FD) events were categorized into four types according to their profile shape. From 1990 to 2020, cosmic ray intensity data from five neutron monitor stations (two subpolar and three mid-latitude) were used. The superposed epoch technique has been used to calculate the vectorial average of the observed diurnal vectors for every day of the four types of FD. It can be found that the subpolar stations (McMurdo and Thule) showed different behavior than the other stations. The solar-diurnal variation at the Thule and McMurdo subpolar stations is comparable on some days to the variation at mid-latitude stations, indicating that CR anisotropy on these days is not the only (and sometimes not the main) source of the solar-diurnal variation. The contribution of the solar-diurnal anisotropy to the diurnal variation at subpolar stations is small, much less than at other neutron monitors.

According to muon hodoscope URAGAN and Moscow neutron monitor, the average annual solar-diurnal anisotropy determined by a local method in quiet periods is obtained and analyzed. Data processing and comparison with the vector anisotropy calculated by the global survey method is discussed. [ABSTRACT FROM AUTHOR]

We address variations in the rigidity spectrum and anisotropy of cosmic rays (CRs) during the 1998 Aug 24 Ground Level Enhancements (GLEs) from the satellite (GOES-10) and ground-based observations at the global network of neutron monitors by using the Spectrographic Global Survey techniques. We also determined CR differential rigidity spectra for different hours of the investigated event. The accelerated proton maximal rigidity in the GLE was shown to be 2.5 GV. [ABSTRACT FROM AUTHOR]

The atmospheric cutoff, similarly to the geomagnetic cutoff, is the lower energy limit for cosmic ray particles that can reach a given location on the ground and be registered by a detector there, e.g., by a neutron monitor. It is caused by the decreasing intensity of a cosmic-ray cascade in the lower atmosphere. Although the geomagnetic cutoff is higher than atmospheric over the most of the Earth's surface, the latter is dominant and therefore defines the neutron monitor count rate in the polar regions. The atmospheric cutoff decreases with the altitude, and this provides additional sensitivity of high-altitude polar neutron monitors to low-energy particles, mainly solar energetic protons during the so-called ground-level enhancement events. In this work, we quantitatively estimated the atmospheric cutoff energies for 21 polar neutron monitor stations in conditions without a significant solar energetic particle event. The cutoff value can be as low as about 300 MeV for protons (VOSTOK and DOMC/DOMB stations), which is notably lower than about 430 MeV at sea level. In addition to that, we estimated the worst case scenario of the strongest-ever observed ground-level enhancement event GLE#05, occurred on the 23rd of February, 1956, and showed that the atmospheric cutoff becomes as low as about 100 MeV. In other words, some neutron monitor stations can register particles with energies of even about 100 MeV during an exceptionally strong solar particle event. It is explained by the highly intensive and soft spectrum of the event in its early delayed phase. [ABSTRACT FROM AUTHOR]

Galactic cosmic rays (GCR) exhibit a small local anisotropy observed as diurnal variability of ground-based neutron monitor (NM) count rates. Since the asymptotic directions of various NMs are different, their ability to observe the GCR diurnal variation also varies. Here we show that the Dome C (DOMC) NM is hardly sensitive to the diurnal variation, with its amplitude being 0.03%, in contrast to other polar NMs whose sensitivity to the diurnal variability ranges from 0.16 to 0.4%. We argue that this is related to the fact that DOMC NM has a narrow asymptotic-direction cone looking nearly to the South pole (geographic latitude above 75°). This makes the DOMC NM a unique detector being the only existing NM accepting cosmic-ray particles originating from the off-equatorial region. This is important for detailed studies of cosmic-ray transport in the vicinity of Earth, specifically for anisotropic solar energetic particle events. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The European Spallation Source ERIC (ESS), currently under construction in Lund, Sweden is a facility established to deliver the highest integrated neutron flux originating from a pulsed source with the aim of supporting an initial fifteen neutron instruments for cutting edge science experiments. This in turn requires reliable monitoring at complex neutron beam lines: in particular, linearity, timing capability, adaptability of the design for various flux ranges (dynamic range) and sensitivity to neutrons within the range of 0.6-10Å are expected from the neutron beam monitors to be installed at the ESS beam lines. Additionally, operational stability and low attenuation are also desirable characteristics for such neutron beam monitoring. A prototype neutron beam monitor based on the ionisation chamber principle and a boron converter, designed by CDT CASCADE Detector Technologies GmbH and ESS, has been investigated at the BER-II research reactor of Helmholtz Zentrum Berlin (HZB). The effort to design and investigate a thermal neutron ionisation beam monitor was initiated by adapting the concept of ionisation chambers previously known elsewhere. So far all the characterised neutron beam monitors discriminate neutron hits on a discrete event basis (pulse mode), whereas the beam monitor prototype introduced in this paper estimates the total flux as a function of current (current mode). While most other neutron beam monitoring devices and detectors rely upon a signal amplifying gain stage, the ionisation chamber operates without any gain and is consequently robust against typical detector ageing effects that compromise the sensitivity over time. The initial tests were performed at the ESS V20 test beam line under realistic conditions resembling those of the future pulses of ESS. The linearity is demonstrated for 3Å pulses in the flux range of 2-3 × 105 n/s/cm2 and for white pulses (0.6-10Å) in the range of 1-5 × 106 n/s/cm2. The timing behaviour resembles the data previously recorded at the V20 beam lines. This novel implementation of a neutron sensitive ionisation chamber shows great promise for beam monitoring and diagnostics at ESS. As the ionisation beam monitor itself is an entirely passive device, it is adequately robust to be employed in areas of high irradiation where no regular servicing or maintenance can be provided. [ABSTRACT FROM AUTHOR]

We have carried out an experimental study of the influence of precipitation in the form of snow on measurements of the neutron flux intensity near Earth's surface. We have examined the state of the snow cover and its density, and found out that the density depends on the depth of the snow cover. Using the experimental results, we estimate the neutron absorption path in the snow. Changes in snow cover by 10–12 cm at a depth of 80 cm are shown to cause variations in the monitor count rate with an amplitude of 0.9 %. At the snow depth of 80 cm, the neutron monitor count rate decreases by about 8 %. The observed variations should be attributed to the meteorological effects of cosmic rays. The absorption coefficient of neutrons in the snow was also found from the correlation between the count rate of the neutron monitor and the amount of snow above the detector. We propose a real-time correction of the neutron monitor data for precipitation in the form of snow. For this purpose, we implement continuous monitoring of the amount of snow cover. The monitoring is provided by a snow meter made using a laser rangefinder module. We discuss the results obtained.

The first ground-level enhancement of the current Solar Cycle 25 occurred on 28 October 2021. It was observed by several space-borne and ground-based instruments, specifically neutron monitors. A moderate count-rate increase over the background was observed by high-altitude polar stations on the South Pole and Dome C stations at the Antarctic plateau. Most of the neutron monitors registered only marginal count-rate increases. Using detrended records and employing a method verified by direct space-borne measurements, we derive the rigidity spectra and angular distributions of the incoming solar protons in the vicinity of Earth. For the analysis, we employed a newly computed and parameterized neutron-monitor yield function. The rigidity spectra and anisotropy of solar protons were obtained in their time evolution throughout the event. A comparison with the Solar and Heliospheric Observatory/Energetic and Relativistic Nuclei and Electron (SOHO/ENRE) experiment data is also performed. We briefly discuss the results derived from our analysis. [ABSTRACT FROM AUTHOR]

In this work we implement an analytically derived coupling function between ground-level and primary proton particles for the case of ground-level enhancement events (GLEs). The main motivation for this work is to determine whether this coupling function is suitable for the study of both major cases of cosmic-ray (CR) variation events, namely GLEs and Forbush decreases. This version of the coupling function, which relies on formalism used in quantum field theory (QFT) computations, has already been applied to Forbush decreases yielding satisfactory results. In this study, it is applied to a GLE event that occurred on 10 September 2017. For the analytical derivations, normalized ground-level cosmic-ray data were used from seven neutron-monitor stations with low cutoff rigidities. To assess and evaluate the results for the normalized proton intensity, we benchmark them with the time series for the proton flux, as recorded by the GOES 13 spacecraft during the same time period. The theoretically calculated results for proton energy ≥ 1 GeV are in general agreement with the recorded data for protons with energy > 700 MeV , presenting a least-squares linear best fit with slope 0.75 ± 0.17 and a Pearson correlation coefficient equal to 0.62. We conclude that the coupling function presented in this work is the first coupling function that is well applicable to both cases of cosmic-ray intensity events, namely GLEs and Forbush decreases. [ABSTRACT FROM AUTHOR]

This paper reports on one of several experiments used to validate MCNP models and processes employed to define a cosmic radiation (CR) neutron source and benchmark to optimise a new ground level neutron monitor (NM) design. The new NM design aims to be more compact, non-toxic and capable of producing comparable counting efficiencies to the NM-64; a monitor standardised in 1964 and which makes up most of the established global network. A broad-energy neutron monitor, the N50L, originally designed for nuclear material accountancy and safeguards, is used to provide primary data in support of our new NM design. Ambient count rate data from the N50L were acquired from it bare and inside a lead (Pb) sarcophagus to boost the neutron signal. Measured data were compared with calculations made using a Monte Carlo N-Particle (MCNP) transport code model of the setup. The calculated compared to the measured count rate for the monitor inside the Pb sarcophagus are in good agreement with a ratio close to one. However, overpredictions (by almost a factor of two) of the calculated rate for the bare monitor suggest inadequacies of the model for high-energy physics. Pressure corrected count rate data were also compared with data from several existing NM-64s over the same period. Our data are in good agreement with variations observed by these existing monitors on the global network. The N50L uses helium-3 (3He) counters and roughly equates to about 1/17th of the proposed final NM design in terms of detector volume. Scaled count rates from the N50L are within 73% of the rates derived from an NM-64 for a similar latitude, geomagnetic cutoff rigidity and altitude, and differs by <8% of the MCNP simulated response of the proposed design. [ABSTRACT FROM AUTHOR]

Forbush decreases (FDs) are sharp reductions of the cosmic-ray (CR) intensity, following intense solar activity such as coronal mass ejections (CMEs) and their corresponding interplanetary shocks. In some cases, shocks create sudden storm commencements (SSCs) at the Earth's magnetosphere with significant interest for space-weather studies. Preincreases and/or predecreases of CR intensity before the onset of FDs, known as precursory signals, have been widely examined by many authors. In this work, an attempt to define precursory signals that are not related to SSCs is presented. For the present analysis, CR data recorded by the ground-based Neutron Monitor Network as well as data on solar flares, CMEs, solar-wind speed, interplanetary magnetic field, and geomagnetic indices for the years 1969 – 2019 are used. To identify FDs that present precursors, the adopted criteria are mainly the FD amplitude (> 2%) and the equatorial CR anisotropy before the onset time (> 0.8%). The analysis of FDs and the study of their asymptotic-longitude CR distribution for precursors are based on the Global Survey Method and the Ring of Stations Method, respectively. Precursory signals are identified in 17 out of 27 events without SSCs. [ABSTRACT FROM AUTHOR]

Abstract High electric fields that occur in thunderstorm clouds in the Earth’s atmosphere might accelerate energetic charged particles produced by cosmic rays. Such energetic particles, especially electrons, can cause additional ionization as they are multiplied and thus form avalanche of relativistic electrons. These relativistic electrons emit Bremsstrahlung in the X- or gamma-ray spectral ranges as they lose their kinetic energy via collisions. Thunderstorm ground enhancements (TGEs) of secondary cosmic ray fluxes recorded at the top of a sharp rocky mountain of Lomnický Štít in High Tatras (2634 m, Slovak Republic) are compared with simultaneous measurements of electric field at the mountain top and on its slope at the observatory of Skalnaté Pleso (1780 m). Results of measurements performed from May to September in 2017 and from May to October in 2018 are presented. The cosmic ray flux is measured by Space Environment Viewing and Analysis Network (SEVAN) and by neutron monitor with 1-s resolution. The TGEs that persisted usually several minutes were mainly detected in the SEVAN channel 1 which has the lowest energy threshold, about 7–8 MeV. A statistical analysis shows that these enhancements usually occurred (not only) during large values of vertical, upward-pointing electric fields measured just above the detector. It is shown that the measurement of electric field at Skalnaté Pleso, distant about 1.86 km from the mountain top is also partly correlated with the enhancements and can provide additional useful information about the distance or dimension of charge structure and dynamics of electric field, especially on short time scales. The enhancements usually did not exceed several tens of percent of background values. However, events that exceeded the background values several times were also recorded. The most extreme event exceeded the background values about 215 times. This event was also detected by other SEVAN channels and by the neutron monitor (~ 130% enhancement), which indicates a possibility of photonuclear reactions. The enhancements were often terminated by a nearby lightning.

Neutron monitors have been the premier ground-based instruments for monitoring the near-Earth cosmic ray flux for more than 70 years. It is essential to continue with such measurements in order to extend this unique long-term time series. Moreover, with the recent interest of the aviation industry to space weather effects, and especially the radiation risk posed by solar energetic particles and galactic cosmic rays, it is vital to extend the current neutron monitor network in order to provide near-real-time measurements to the space weather community. In this paper we discuss a new electronics system that was retrofitted to the SANAE neutron monitor in Antarctica. We present initial results from this system, featuring very high temporal resolution and discuss the techniques applied to the data analysis. Based on these successful upgrades, we are confident that this system can be used to rejuvenate the aligning neutron monitor network, and even possibly to revive some of the decommissioned instruments. [ABSTRACT FROM AUTHOR]

SHICRA SB RAS, using data from the NMDB database, has implemented continuous monitoring of the dynamics of cosmic ray (CR) distribution parameters and the automatic forecasting of geomagnetic disturbance. Monitoring is based on the global survey method, which considers the world-wide network of neutron monitors as a single device oriented in different directions at each measured time. This method provides real-time parameters of nine components of the first two angular moments of the CR distribution function for each hour of observation. This paper discusses methodological aspects related to the use of the global survey method and some results of the forecasting of geomagnetic disturbances for 2017–2018.

Cosmic rays, high-energy subatomic particles of extraterrestrial origin, are systematically measured by space-borne and ground-based instruments. A specific interest is paid to high-energy ions accelerated during solar eruptions, so-called solar energetic particles. In order to build a comprehensive picture of their nature, it is important to fill the gap and inter-calibrate ground-based and space-borne instruments. Here, we focus on ground-based detectors, specifically neutron monitors, which form a global network and provide continuous recording of cosmic ray intensity and its variability, used also to register relativistic solar energetic particles. The count rate of each neutron monitor is determined by the geomagnetic and atmospheric cut-offs, both being functions of the location. Here, on the basis of Monte Carlo simulations with the PLANETOCOSMICS code and by the employment of a new verified neutron monitor yield function, we assessed the atmospheric cut-off as a function of the altitude, as well as for specific stations located in the polar region. The assessed in this study altitude profile of the atmospheric cut-off for primary cosmic rays builds the basis for the joint analysis of strong solar proton events with different instruments and allows one to clarify recent definitions and related discussions about the new sub-class of events, so-called sub-ground-level enhancements (sub-GLEs). [ABSTRACT FROM AUTHOR]

Ground level enhancements (GLEs) are space weather events that pose a potential hazard to the aviation environment through single event effects in avionics and increased dose to passengers and crew. The existing ground level neutron monitoring network provides continuous and well‐characterized measurements of the radiation environment. However, there are only a few dozen active stations worldwide, and there has not been a UK‐based station for several decades. Much smaller neutron detectors are increasingly deployed throughout the world with the purpose of using secondary neutrons from cosmic rays to monitor local soil moisture conditions (COSMOS). Space weather signals from GLEs and Forbush decreases have been identified in COSMOS data. Monte Carlo simulations of atmospheric radiation propagation show that a single COSMOS detector is sufficient to detect the signal of a medium‐strength (10%–100% increase above background) GLE at high statistical significance, including at fine temporal resolution. Use of fine temporal resolution would also provide a capability to detect Terrestrial Gamma Ray Flashes (via secondary neutrons) which are produced by certain lightning discharges and which can provide a hazard to aircraft, particularly in tropical regions. We also show how the COsmic‐ray Soil Moisture Observing System‐UK detector network could be used to provide warnings at the International Civil Aviation Organization "Moderate" and "Severe" dose rate thresholds at aviation altitudes, and how multiple‐detector hubs situated at strategic UK locations could detect a small GLE at high statistical significance and infer crucial information on the nature of the primary spectrum. Plain Language Summary: Space weather events can lead to significant increases in the intensity of the atmospheric radiation environment, including at ground level. These ground level enhancements (GLEs) have been detected by a global network of neutron monitors for over 70 years. However, these instruments are expensive to construct and maintain. Only a few dozen are currently active, with no station located in the United Kingdom for several decades. As part of an effort to improve the resilience of UK infrastructure to space weather, we have studied the possibility of using alternative detectors to supplement neutron monitor measurements. COSMOS detector networks in the United Kingdom, North America, Australia and elsewhere use variations in ground level neutron flux to infer information on local soil moisture conditions for hydrological applications. We show that these same detectors could be dual‐purposed to provide information on GLEs that would complement the global neutron monitor network by providing much finer spatial resolution and, therefore, a highly localized warning system for space weather threats to aviation. Key Points: Data from cosmic ray neutron sensor (CRNS) networks have been reprocessed and analyzed in the novel context of Space WeatherGround level enhancements from solar cycle 24 present weak signals in the dataMonte Carlo simulations show such CRNS networks are suitable for dual‐purposing as space weather detectors [ABSTRACT FROM AUTHOR]

A method for forecasting geomagnetic storms using the realization of the global survey method in real time is presented. The method is based on data from the worldwide network of neutron monitors NMDB. Using this method, we analyze the behavior of components of three-dimensional angular distribution of cosmic rays in the interplanetary medium, which were due to the first two spherical harmonics, over the period from 2013 to 2018. We have established that the main parameters that respond to the arrival of geoeffective disturbances of the interplanetary medium at Earth are changes in amplitudes of zonal (north-south) components of cosmic ray distribution. In order to select effective criteria for identifying predictors of geomagnetic disturbances and their possible temporal variations, we have made a retrospective analysis of the relationship between behaviors of the above components and geomagnetic disturbances occurring during the period of interest.

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. [ABSTRACT FROM AUTHOR]

Muon detectors and neutron monitors were recently installed at Syowa Station, in the Antarctic, to observe different types of secondary particles resulting from cosmic ray interactions simultaneously from the same location. Continuing observations will give new insight into the response of muon detectors to atmospheric and geomagnetic effects. Operation began in February, 2018 and the system has been stable with a duty-cycle exceeding 94%. Muon data shows a clear seasonal variation, which is expected from the atmospheric temperature effect. We verified successful operation by showing that the muon and neutron data are consistent with those from other locations by comparing intensity variations during a space weather event. We have established a web page to make real time data available with interactive graphics (http://polaris.nipr.ac.jp/cosmicrays/). [ABSTRACT FROM AUTHOR]

The study of the nature of variations in cosmic ray fluxes, including diurnal, 27-day, annual, etc., and the question of the relationship of solar-geophysical factors on the state of the atmosphere attracts special attention of scientists. Coronal mass ejections are the result of solar winds generated on the Sun during a series of flares. At the same time, solar winds provoke variations in the intensity of cosmic rays, which include, in particular, Forbush-decreases. The article presents brief characteristics of the CARPET detector of the scientific cosmophysical complex of the L.N.Gumilyov ENU and experimental data obtained at this facility during the observation of Forbush-deacreases in July and September 2017. The results of the analysis of variations in cosmic ray fluxes are presented and their relationship with the conditions in the interplanetary medium and the Earth's magnetosphere caused by processes on the Sun is described. It was found that the decrease in cosmic ray fluxes in July and September 2017 was due to high solar activity (a series of solar flares). A comparative analysis of the time changes recorded by the CARPET detector modules of the L.N.Gumilyov ENU scientific complex with the data of the world network of neutron monitors («Apatity», «Almaty» and «Jungfraujoch IGY») is also presented. Data on the electromagnetic environment of interplanetary space during the period of heliospheric and magnetospheric disturbances were also used for the analysis. The analysis showed that the measurement data of the CARPET detector is in good agreement with the data of the above-mentioned neutron monitors of the world network, which allows us to study the physical nature of cosmic ray variations for different time intervals. [ABSTRACT FROM AUTHOR]

Solar modulation of galactic cosmic rays around the solar minimum in 2019–2020 looks different in the secondary neutrons and muons observed at the ground. To compare the solar modulation of primary cosmic rays in detail, we must remove the possible seasonal variations caused by the atmosphere and surrounding environment. As such surrounding environment effects, we evaluate the snow cover effect on neutron count rate and the atmospheric temperature effect on muon count rate, both simultaneously observed at Syowa Station in the Antarctic (69.01° S, 39.59° E). A machine learning technique, Echo State Network (ESN), is applied to estimate both effects hidden in the observed time series of the count rate. We show that the ESN with the input of GDAS data (temperature time series at 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, and 20 hPa) at the local position can be useful for both the temperature correction for muons and snow cover correction for neutrons. The corrected muon count rate starts decreasing in late 2019, preceding the corrected neutron count rate which starts decreasing in early 2020, possibly indicating the rigidity-dependent solar modulation in the heliosphere.

The Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission provided long‐term measurements of 10s of megaelectron volt (MeV) inner belt (L < 2) protons (1992–2009) as did the Polar‐orbiting Operational Environmental Satellite‐18 (POES‐18, 2005 to present). These long‐term measurements at low‐Earth orbit (LEO) showed clear solar cycle variations which anticorrelate with sunspot number. However, the magnitude of the variation is much greater than the solar cycle variation of galactic cosmic rays (>GeV) that are regarded as a source of these trapped protons. Furthermore, the proton fluxes and their variations sensitively depend on the altitude above the South Atlantic Anomaly (SAA) region. With respect to protons (>36 MeV) mirroring near the magnetic equator, both POES measurements and simulations show no obvious solar cycle variations at L > 1.2. This is also confirmed by recent measurements from the Van Allen Probes (2012–2019), but there are clear solar cycle variations and a strong spatial gradient of the proton flux below L = 1.2. A direct comparison between measurements and simulations leads to the conclusion that energy loss of trapped protons due to collisions with free and bound electrons in the ionosphere and atmosphere is the dominant mechanism for the strong spatial gradient and solar cycle variation of the inner belt protons. This fact is also key of importance for spacecraft and instrument design and operation in near‐Earth space. Key Points: The solar cycle variation of inner belt protons measured by LEO satellites is mainly due to losses from atmospheric collisionsInner belt proton intensity and variation measured at LEO sensitively depend on the altitude above the SAAMeasurements and simulations reveal a strong spatial gradient of trapped protons mirroring near the magnetic equator below L = 1.2 [ABSTRACT FROM AUTHOR]

Neutron monitor counting rates and solar wind velocity, interplanetary magnetic field, sunspot number and total solar irradiance measurements from 2013 to 2018 corresponding to the end of solar maximum and the decreasing phase of the Solar Cycle 24 have been used. The main objective is to check whether the periodicities observed in the cosmic rays are affected by the magnetic rigidity or the height at which the neutron monitors are placed. A Global Neutron Monitor (GNM) has been defined as representative of the neutron monitor global network. This GNM is constructed by averaging the counting rates of a set of selected neutron monitors. The selection process is based on the combination of three new data quality criteria, which are applied to neutron monitors in the Neutron Monitor Data Base giving a final pool of 22 selected neutron monitors. Morlet wavelet analysis is applied to the GNM and the selected solar activity parameters to find the common periodicities. Short-term periodicities of 13.5, 27, 48, 92, 132 and 298 days have been observed in cosmic ray intensity. A clear inverse relationship between rigidity and spectral power has been obtained for the 13.5-, 48-, 92-, 132-day periods. A not so clear but still observed direct relationship between the height of the neutron monitors and the spectral power for the 48-, 92-, 132-day periods has been also found. The periodicity of 92 days is the one which shows the highest dependence with rigidity cutoff and height. As far as we know, this is the first time that these dependencies are reported. We think that these observations could be explained by assuming some cosmic ray intensity energy dependence in such periodicities and a competitive effect between rigidity and height. [ABSTRACT FROM AUTHOR]

High electric fields that occur in thunderstorm clouds in the Earth's atmosphere might accelerate energetic charged particles produced by cosmic rays. Such energetic particles, especially electrons, can cause additional ionization as they are multiplied and thus form avalanche of relativistic electrons. These relativistic electrons emit Bremsstrahlung in the X- or gamma-ray spectral ranges as they lose their kinetic energy via collisions. Thunderstorm ground enhancements (TGEs) of secondary cosmic ray fluxes recorded at the top of a sharp rocky mountain of Lomnický Štít in High Tatras (2634 m, Slovak Republic) are compared with simultaneous measurements of electric field at the mountain top and on its slope at the observatory of Skalnaté Pleso (1780 m). Results of measurements performed from May to September in 2017 and from May to October in 2018 are presented. The cosmic ray flux is measured by Space Environment Viewing and Analysis Network (SEVAN) and by neutron monitor with 1-s resolution. The TGEs that persisted usually several minutes were mainly detected in the SEVAN channel 1 which has the lowest energy threshold, about 7–8 MeV. A statistical analysis shows that these enhancements usually occurred (not only) during large values of vertical, upward-pointing electric fields measured just above the detector. It is shown that the measurement of electric field at Skalnaté Pleso, distant about 1.86 km from the mountain top is also partly correlated with the enhancements and can provide additional useful information about the distance or dimension of charge structure and dynamics of electric field, especially on short time scales. The enhancements usually did not exceed several tens of percent of background values. However, events that exceeded the background values several times were also recorded. The most extreme event exceeded the background values about 215 times. This event was also detected by other SEVAN channels and by the neutron monitor (~ 130% enhancement), which indicates a possibility of photonuclear reactions. The enhancements were often terminated by a nearby lightning. [ABSTRACT FROM AUTHOR]

In December 2015, we have installed neutron monitors at the Jang Bogo station in Antarctica. The Jang Bogo station is the second science station which is located at the coast (74° 37.4´S, 164° 13.7´E) of Terra Nova Bay in Northern Victoria Land of Antarctica. A neutron monitor is an instrument to detect neutrons from secondary cosmic rays collided by the atmosphere. The installation of neutron monitor at Jang Bogo station is a part of transferred mission for neutron monitor at McMurdo station of USA. Among 18 tubes of 18-NM64 neutron monitor, we have completed relocation of 6 tubes and the rest will be transferred in December 2017. Currently, comparison of data from the neutron monitors of both two stations is under way and there is a good agreement between the data. The neutron monitors at Jang Bogo station will be quite useful to study the space weather when the installation is completed.

The 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. Key Points: Direct validation of the NM yield function is performed using the proton and helium spectra measured by AMS‐02 for the period of 2011‐2017The NM yield function by Mishev et al. (2013) is fully validated, while others need revisionsThe use of the force field approximation to fit the measured proton spectra is validated within +/‐10% [ABSTRACT FROM AUTHOR]

As a result of intense solar activity during the first 10 days of September, a ground level enhancement occurred on 10 September 2017. Here we computed the effective dose rates in the polar region at several altitudes during the event using the derived rigidity spectra of the energetic solar protons. The contribution of different populations of energetic particles, namely, galactic cosmic rays and solar protons, to the exposure is explicitly considered and compared. We also assessed the exposure of a crew members/passengers to radiation at different locations and at several cruise flight altitudes and calculated the received doses for two typical intercontinental flights. The estimated received dose during a high latitude, 40 kft, ∼10‐hr flight is ∼100 μSv. Plain Language Summary: As a result of intense solar activity during the first 10 days of September, a ground level enhancement occurred on 10 September 2017. We computed the exposure, namely, the effective dose rates in the polar region at several altitudes during the event using the derived spectra of the solar protons. The contribution of different populations of energetic particles, namely, galactic cosmic rays and solar protons, to the exposure is explicitly considered and compared. We also assessed the exposure of a crew members/passengers to radiation at different locations and at several cruise flight altitudes and calculated the received doses for two typical intercontinental flights. Key Points: Rigidity spectra of solar energetic protons during the GLE 72 were reconstructed using data from the global neutron monitor networkTime profiles of the effective dose rates at several altitudes during the GLE 72 were estimatedReceived doses for crew/passenger of a typical intercontinental high‐latitude ∼10‐hr flight were estimated as ∼100 μSv [ABSTRACT FROM AUTHOR]

Due to confusion in the proof correction process, the author’s proof corrections were not correctly taken into account. The corrections are listed below, highlighted by a boldface font.