Executive Summary Chapter 1 History, heritage and operation
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Acknowledgements Forward Executive Summary Chapter 1 History, heritage and operation Chapter 2 Cosmic-ray and Heliospheric Science Chapter 3 Hydrology Geoscience and Glaciology?? Chapter 4 Private sector Aspects Chapter 5 Service to government agencies, domestic and international Chapter 6 Space Weather Chapter 7 Current status and outlook Chapter 8 Recommendations and priorities Chapter 9 Citation Listing Acknowledgements The National Science Foundation, the University of New Hampshire and the Bartol Research Institute sponsored a workshop entitled Neutron Monitor Community Workshop on October 24-25, 2015 in Honolulu, Hawaii. The workshop was organized with generous help from the University of Hawaii at Manoa. Its objective was to review and evaluate the US-supported neutron monitor network, and articulate a community consensus on the network utility and value with recommended priorities and actions. This paper is the principal product of that workshop, integrating contributions of the many participants. Workshop participants
Neutron monitors were identified decades ago as useful instruments for studying the near Earth environment. Since their wide deployment in the International Geophysical Year 1957-1958, they have been used to (1) measure the energetic particle emission from the Sun during periods of intense solar activity, (2) study the dynamics of the near and far heliosphere as sensed through solar modulation over the course of several solar cycles and (3) study the dynamics of what are now known as Coronal Mass Ejections through the transient modulation of galactic cosmic rays. Since then others have found uses for neutron monitor data that go beyond near-Earth science… For the technically inclined reader, the initial chapter addresses the history and workings of the instrument and its modes of deployment. The remainder of the paper is organized into discussions of the utility and importance of neutron monitors for science, service and space weather. The paper finishes with a discussion of recommended actions and priorities to support these diverse needs.
A neutron monitor workshop held in October 2015 reviewed the status, utility, science and future of the monitor network. The participants formulated recommended actions to preserve and enhance these aspects of the network. Also in October 2015, two documents from the Executive Branch were published in response to the country’s needs from the risks posed by Space Weather events, the National Space Weather Strategy and the National Space Weather Action Plan. The documents were prepared by the Space Weather Operations, Research, and Mitigation (SWORM) Task Force and published by the National Science and Technology Council. Co-chairs of the task force included the National Oceanic and Atmospheric Administration, Department of Homeland Security and the Office of Science and Technology Policy. The role of neutron monitors in the multi-agency plan is part of the multipronged approach to identify and characterize space weather events and mitigate their negative effects on society and governmental functions. A neutron monitor is a ground-based instrument that continuously records the rate of high-energy particles (E>500MeV) impacting the Earth’s atmosphere. For historical reasons these particles, mostly protons and helium nuclei, are called "cosmic rays." The advent of the neutron monitor came after the discovery by Simpson [1948] that the intensity of nucleonic component in cosmic ray air showers is several times more sensitive to changes in low energy primary cosmic rays than that of the electromagnetic and muon components. In 1952 the first neutron monitor stations were established at Chicago, Climax, Huancayo and Sacramento Peak. The reliability and basic simplicity of neutron monitors provide a means for studying the longer-term variations, while the sensitivity to low energy primary cosmic rays and high count rates make possible the measurement of short term intensity changes. Because the intensity of cosmic rays hitting Earth is not uniform, it is important to place neutron monitors at multiple locations to form a complete picture of cosmic rays in space. As the result of the long term reliability and on-line availability of neutron monitor data, users outside the traditional circles of Space Sciences have discovered innovated ways to utilize these data for new and unforeseen investigations, radiation monitoring or for improving real-time background knowledge. Over past decades neutron monitor data have become an operational resource in many different areas. Unfortunately, from the point of view of basic science, service to the community and as part of the national space weather strategy, the current state of the neutron monitor network is not good. The network now consists of aging neutron monitors, many of which have been neglected due to a lack of funding. The network is not functioning as it once did or envisioned during the International Geophysical Year in 1957-1958. Several key measurement sites have been de-commissioned or switched off. A perceived lack of interest by the US makes foreign sites consequently vulnerable to cuts and closings. There is minimal coordination between supporting groups with each neutron monitor station fighting for existence. New and inexpensive technology cannot make its way into the field to modernize and greatly improve the performance of those stations now operating. Recommendations emerged from the workshop that if implemented would bring the network into a condition to conduct the best science and support operational needs. In order of priority, they are:
History, heritage and operation 
Figure 1. Anatomy of a cosmic ray air shower. During the decades from 1930s to 1940, a wide variety of experiments confirm primary cosmic rays entering the top of the atmosphere produced nuclear interactions deep in the atmosphere. An incoming primary cosmic ray with sufficient energy will interact with an air nuclei, initiating a cascade of secondary interactions that ultimately produce a particle shower. A significant fraction of these interactions occur at the nuclear level which can be thought of as a two stage process. In the first stage, the primary particle reacts with nucleons inside the nucleus creating an intranuclear cascade of high-energy (>20 MeV) protons, neutrons, and pions within the nucleus. Some of these energetic hadrons escape as secondary particles while others deposit their energy in the nucleus leaving it in an excited state. The escape secondaries may collide with another air nuclei and produce successively spallation products and excited nuclei. In the second stage (nuclear de-excitation), evaporation takes place when the excited nucleus relaxes by emitting low-energy (< 20 MeV) neutrons, protons, alpha particles, etc., with the majority of the particles being neutrons. Evaporation neutrons interactions with nuclei are typically elastic that transfer energy without changing the structure of the nucleus. After multiple interactions, the evaporation neutron will lose energy and eventually thermalize, and/or be absorbed or undergo decay. In 1946, Simpson initiated the first investigation on the dependence of nucleonic intensity with incident primary cosmic-ray energy using the geomagnetic cut-off effect on a B29 aircraft at 30,000ft. The nucleonic flux in the atmosphere was inferred by measurements of the evaporation energy neutron intensity (Simpson, 1949). This required a detector that was insensitive to neutron energies lower than the evaporation energy, as thermal neutrons are highly dependently on local conditions. An additional requirement was the exclusion of the muon and electron components at all energies. To achieved these requirements, Simpson designed a detector utilizing a 10BF3 gas proportional counters encapsulated in paraffin. 10B has a neutron capture cross-section inversely proportional to the neutron and responds to neutrons by the exothermic reaction 10B(n,) 7Li with a Q value of 2.3MeV. With properly chosen gas density, the pulse-height threshold could eliminate the muon and electromagnetic component from neutron absorptions. Paraffin serves to reduce the energy of neutrons, thus increasing the probability of an absorption inside the counter while also providing a barrier against unwanted thermal and epithermal energy neutrons. 
Figure 2. The lower curve represents the latitude dependence for ionization chamber. The upper curve represents the evaporation neutron intensity. Both curves are normalized to 1 at zero magnetic latitude. The data for the curves were obtained in June, 1948. (Need Permission?) Utilizing this new neutron detector along with Geiger-Muller counters on an air-borne latitude measurements in 1946–1947, Simpson [1948] discovered the latitude variation of the intensity of evaporation neutrons in the atmosphere is several times larger than that of the ionizing and hard components. It immediately became apparent from this discovery that variations in the low energy cosmic-ray proton intensity down to 1–5 GV could be investigated continuously for the first time. This new detector opened a new window to the primary cosmic-ray energy spectrum. The observed variation in the nucleonic component intensity at high latitudes from survey to survey motivated the need for a ground base system to continuously monitor the evaporation neutrons. It was during this time Simpson (2000) considered the effect of atmospheric production and local production of evaporation of neutrons, estimating that the multiplicity of neutron production in elements of high atomic mass, A, increased as A0.4 per gram. This idea led to the conception of a cosmic-ray neutron monitoring system based on measuring the local production of evaporation neutrons in a high atomic mass target such as lead. The fragmentation of a lead nucleus by an incident high-energy secondary nucleon would yield a multiplicity of evaporation neutrons, which would then become thermalized in the surrounding paraffin wax and be detected with 10BF3 proportional counters embedded in the ‘pile’. The development of a leaded neutron monitor was undertaken and in 1949, these studies led to a basic ‘standard’ pile design with an account of its dependence only on barometric pressure (Simpson, 1953; Simpson et al., 1953b). Furthermore, this design could be extended in size to multiply the counting rate from the pile. The 12 counter configuration became the standard neutron monitor design for Chicago and Climax, Colorado in 1949; and with the influence of Scott Forbush, later it was the design adopted for the International Geophysical Year (1957–1958) at more than sixty (60) sites world-wide (Simpson, 1958). The detector was renamed the IGY neutron monitor. 
Figure 3. IGY Neutron Monitor 
Figure 4.Cross-sectional view of an NM64 Neutron Monitor Scott Forbush identified the primary characteristics of the majority of cosmic ray time variations utilizing continuous observations from four different ground-based ionization chambers over the period from 1937 to 1952 (Forbush, 1954). The inclusion of the IGY neutron monitors opened the opportunity to measure the intensity changes in the cosmic-ray primaries down to 1GeV for the first time and allowing a means to correctly identify the source of these variations revealing an understanding of six basic phenomena: (1) Variation of cosmic ray intensity with geomagnetic latitude (Simpson, 1948). (2) Variation of cosmic radiation intensity in response to the 11-year solar activity cycle and the 22-year solar magnetic cycle (Meyer and Simpson, 1955) that was originally indicated in ion chamber data variations from the time period 1937–1952 by Forbush (1954). (3) Correlation of the 27 day modulation of cosmic ray intensity with the Carrington rotation of the Sun (Simpson, Babcock and Babcock, 1955). (4) Anisotropy of the cosmic rays exhibited as diurnal variations (Simpson 1953). (5) The origin of the rapid decrease in cosmic ray intensity (Forbush Decrease) lies outside of the Earth’s geomagnetic field (Simpson 1953). (6) Based on the ground level event observation that the sudden and short burst of relativistic nucleons of a solar flare event (23 February 1956) could only slowly escape to the interstellar medium through a continuous barrier region beyond the orbit of Earth, implying a dynamical heliosphere (Bieber et al., 2000, Meyer et al., 1956; Simpson, 1985; Parker, 1956). Following these discoveries, Parker (1963) developed a quantitative theory for coronal expansion of the solar wind into interplanetary space. This was the start of our current understanding of the heliosphere and the cosmic ray modulation In 1964 a new neutron monitor design was developed (H. Carmichael, 1964, Fowler 1962, Hatton 1971) to greatly increase the neutron counting rates. The new design was then called the super-monitor and now simply the NM64. Such an increase (to over an order of magnitude larger than the IGY monitor) involved designing a neutron monitor to cover a greater area than that of the IGY monitor. This was achieved by utilizing much larger (BP28) BF3 proportional counters developed at Chalk River by Fowler (1962). Another design advancement was the use of polyethylene as a moderator and reflector which provided a more stable mechanical structure. Although the lead producer and moderator were chosen to be similar to that of the IGY, the reflector thickness was reduced from 11 inches to 3 inches based on an optimization study by Hatton and Carmichael (1964) with the objective to maximize neutrons counts above evaporation energies while minimizing the contribution from externally produced evaporation neutrons. Most importantly the NM64 design has achieved a globally accepted standardization (Hatton 1971). Neutron Monitor Operation In a neutron monitor, neutron sensitive proportional tubes, surrounded by moderator material and a lead target, detect near-thermal neutrons produced locally in the lead from interacting incident particles. Even though neutrons do not leave an ion trail in the proportional tube, the absorption of a neutron by a nucleus is usually followed by the emission of charged particles which can be detected. A proportional tube filled with either 10BF3 or 3He gas responds to neutrons by the exothermic reaction 10B(n,) 7Li or 3He(n, p) 3H. The reaction cross-sections for both nuclei is inversely proportional to the neutron speed, having a thermal endpoint (0.025 eV) of roughly 3840 barns and 5330 barns respectively Surrounding each counter is a moderator which serves to reduce the energy of neutrons, thus increasing the probability of an absorption inside the counter while also providing a reflecting medium for low energy neutrons. The moderator material is chosen to contain a significant fraction of hydrogen as the energy loss per neutron elastic collision increases with decreasing atomic mass A  . The neutron elastic interaction pathlength of hydrogen in typical moderator materials is roughly 1 cm (En =1 MeV) and each inter action reduces the incident neutron energy by a factor of 2 on the average. The lead producer, which surrounds the moderator, provides a thick large-nucleus target for inelastic interactions in which secondary neutrons are produced. A high atomic mass (A) is preferred in the producer as the neutron production rate per unit mass of a material is roughly proportional to ~A0.7. Surrounding the lead is an outer moderator, usually referred to as to the reflector, which serves to contain low energy neutrons produced in interactions within the lead as well as reject unwanted low-energy neutrons produced in the local surroundings from entering into the detector. In most stations each counter has a dedicated electronics interface that registers the total number of pulses that occur above a threshold over different integration times, however a new generation of electronics recently developed by Bartol Research Institute, also records the time between pulses. These are currently in operation at the Newark and Thailand stations. The average number of evaporated neutrons generated in an interaction is energy dependent and can be roughly described as a power law, consequently spectral information could in principle be extracted the timing data.
Figure 4. Calculated Neutron Monitor NM64 detection response to different ground level incident particles. Symbols represent measurements of neutron beam at an accelerator facility, Above shows the expected detection response of a NM64 to ground level particles. It is clear from this calculation the detector design is optimized to measure the hadronic component of ground level secondaries. The NM response from muons above 1 GeV is roughly 3.5 orders of magnitude below the hadrons. In this energy region, the primary mechanisms for muon induced counts are neutron production in photo-nuclear interactions and electromagnetic showers resulting in multiple ionization tracks in a counter. Below 1 GeV, stopping negative charge muons are captured by a lead nucleus into a mesic orbit and absorbed by the nucleus. The de-excitation of the nucleus occurs with the emission of neutrons which is reflected in the rise in detection efficiency with decreasing energy. Through the Giant dipole resonance, incident gamma rays and electron-induced brems may result in a number of de-excitation events. 
Figure 6. Neutron Monitor sea-level response to primary cosmic rays for different solar modulation spectra. For comparison the Compton counter, the Forbush ionization monitor, response function is also displayed. Compton counters (also known as the Compton-Wollan-Bennett ionization chambers) are 12” diameter spherical ionization detectors filled with argon to 50 atmospheres. It measures the rate of charged particles that pass through the active volume (primarily muons and electrons). As shown the NM is sensitive to lower energy primary particles than that of ionization chamber. Even today the peak response of an NM to primary cosmic rays covers the lowest energy regime of the primary spectrum than that of any other ground detector. (Is this needed?) 
Science and Societal impact Neutron monitors have been in operation for over seventy years, and they provide a vital long-term perspective on solar variations with time scales such as the Schwabe cycle (eleven years) or Hale cycle (twenty-two years). At the same time, neutron monitors continue to make valuable measurements at much shorter time scales, providing information on relativistic solar particles and on transient, solar-induced variations of Galactic cosmic rays such as Forbush decreases. The scientific return from neutron monitors is enhanced when they are linked together in coordinated multi-national arrays. Indeed in most modern applications the “instrument” is the array itself, and not any single detector in it. Analysis of intensities from different arrival directions permits determination of the cosmic ray anisotropy, while analysis of detectors at different geomagnetic cutoffs provides information on the energy spectrum. Coordinated arrays now in operation include the 12-station Spaceship Earth network, which is optimized for measuring the angular distribution of relativistic solar energetic particles (Bieber et al. 2004), and the Neutron Monitor Database (NMDB) recently organized under auspices of the European Union (Mavromichalaki 2010). Need space weather introduction In addition to space science and space weather forecasting, data from neutron monitors are also used to determine the flux of neutrons produced by cosmic rays for a broad range of practical applications, including detecting nuclear threats for homeland and national security, calculating the radiation dose to airplane crews and passengers, understanding the rate of single-event upsets (soft errors) in microelectronic devices, measuring soil moisture content, and calculating the production rate of cosmogenic radionuclides used for atmospheric tracers and nuclear treaty verification. In all these applications, neutrons and other secondary particles produced in the atmosphere and surface materials by galactic cosmic rays (and occasionally by solar particles) are either the source of the effect or an important background. Starting from the cosmic-ray local interstellar spectrum or interplanetary spectrum together with a model of the geomagnetic field, the flux and energy spectrum of cosmic-ray-produced neutrons can be calculated using Monte Carlo computer codes to model radiation transport through the atmosphere as a function of altitude/air pressure, geomagnetic cutoff rigidity, and local materials, but the effect of solar modulation on the neutron flux near the Earth’s surface at a given time must come from neutron monitor data. Without ongoing data from stable neutron monitors the cosmogenic neutron flux cannot be determined accurately, and all the practical calculations and measurements that depend on knowing the neutron flux will be severely impaired. The societal impact of these applications and how each application relies on neutron monitor data will be described in subsequent sections of this report. 
Past and present US supported stations First cut at the map. Station names should be added, along with dates Contributions NEUTRON MONITOR NETWORKS The scientific value of neutron monitors is greatly enhanced when they are linked together in coordinated multi-national networks. Indeed in many modern applications the observing “instrument” is the network itself, and not any single detector in it. Analysis of intensities from different arrival directions permits determination of the cosmic ray angular distribution, while analysis of detectors at different geomagnetic cutoffs provides information on the energy spectrum. Solar Energetic Particles. The mechanism by which energetic particles scatter and diffuse in collisionless plasma remains a key problem in astrophysics. Detailed information on transport conditions in the interplanetary medium, such as the scattering mean free path, can be obtained from modeling the time-intensity and time-anisotropy profiles of solar energetic particles (Palmer 1982; Bieber et al. 1994). Anisotropy information from neutron monitor networks is crucial for this modeling, because it permits diffusive delays in the solar wind to be distinguished from extended acceleration or release at the solar source. In turn, the analysis provides information on the particle injection profile at the Sun for comparison with solar radio and optical signatures. Neutron monitors of the 4-nation Spaceship Earth network (Bieber et al. 2004) were deployed to provide optimal coverage of solar particle anisotropies, using existing monitors where possible and constructing new ones as needed. Solar Wind Disturbances. Pioneering observations of the anisotropy of Galactic cosmic rays (Pomerantz and Duggal 1971 and references therein) typically employed a single ground-based detector and relied on Earth’s rotation to provide a range of viewing directions. Often results were expressed as annual means, because it was necessary to average over long periods in order to extract the minuscule anisotropy signal from the many other variations present. Now, with a network observing multiple directions simultaneously it is possible to extract the anisotropy with much better time resolution, often to 1 hour or better. Thus it becomes possible to study transient anisotropies in the pre-existing Galactic cosmic ray population produced by solar wind disturbances such as ICMEs. Reported effects include: bidirectional streaming, indicative of a closed magnetic field topology (Dvornikov et al. 1983; Richardson et al. 2000); gradient anisotropies, which permit determination of the cosmic ray spatial gradient and thereby provide clues to ICME geometry (Bieber and Evenson 1998); and precursor “loss-cone” anisotropies that potentially can provide up to ~12 hours advance warning of major geomagnetic storms (Leerungnavarat et al. 2003 and references therein). 
Figure X. Stack plot of neutron monitor time profiles during a solar active period in 2011, arrayed from highest to lowest energy. Station name and geomagnetic cutoff in GV are shown at right. Differing energy responses to the solar disturbance are obvious. This is a screen capture of a real-time plot available at http://neutronm.bartol.udel.edu/~pyle/SpectralPlot.png. Energy Spectrum. The energy spectrum of cosmic ray variations can be deduced from a network of neutron monitors deployed over a range of geomagnetic cutoffs. For instance, Tylka and Dietrich (2009) used cutoff arrays to extend the spectrum of solar energetic particles from spacecraft energies to the neutron monitor energy range, while Oh et al. (2013) derived information on the spectrum of Galactic cosmic rays during the recent very weak solar minimum and accompanying record maximum in Galactic cosmic rays. Effective cutoffs for neutron monitors range from the atmospheric threshold of ~1 GV to a geomagnetic maximum cutoff of ~17 GV, corresponding to energies ~400 MeV – 16 GeV for protons. As illustrated in Figure X, the response of cosmic rays to a solar wind disturbance in 2011 varies dramatically over this energy range. Solar Neutrons. The Sun on occasion emits relativistic neutrons with sufficient intensity to be detectable by neutron monitors (Chupp et al. 1987; Shea et al. 1991; Bieber et al. 2005). Such events provide exceptionally clear insights into acceleration/injection processes at the Sun, because the neutrons travel straight from the source to the observer unimpeded by magnetic fields. (Non-relativistic neutrons are typically not observed at 1 AU because their decay time, ~15 min, is shorter than the transit time.) An optimal network for observing these events would employ low-latitude, high-altitude monitors sited to minimize atmospheric attenuation and thus increase both the probability of detection and the size of the neutron signal. Space Weather Applications. Linking neutron monitors together in a realtime network enables a number of space weather forecasting and “nowcasting” applications (Kuwabara et al. 2006a; Mavromichalaki et al. 2011). Backtesting studies have shown that automated detection of a Ground Level Enhancement (GLE) onset can provide ~10-30 minutes earlier warning of a major radiation storm than the earliest proton alert issued by the Space Weather Prediction Center (Kuwabara et al. 2006b; Souvatzoglou et al. 2009). Three such GLE alert systems are currently in operation by the University of Delaware (http://www.bartol.udel.edu/~takao/ neutronm/glealarm/), IZMIRAN (http://cr0.izmiran.ru/GLE-AlertAndProfilesPrognosing/), and the National & Kapodistrian University of Athens (http://cosray.phys.uoa.gr/index.php/ glealertplus). Existing systems could be substantially improved if realtime communications could be implemented at additional remote stations (e.g., the U.S. station at South Pole and the Russian station at Tixie Bay). Numerous other space weather applications of neutron monitors have been proposed. For instance, the possibility of near-term forecasting the energy spectrum of solar energetic particle events has been demonstrated in principle (Oh et al. 2012), as has the possibility of nowcasting radiation levels on Earth’s surface during GLE (Mavromichalaki et al. 2011; see their Fig. 6). Additional proposed applications include the use of “loss cone” anisotropies to warn of approaching ICME (Leerungnavarat et al. 2003 and references therein), and prediction of the north-south orientation of the IMF (i.e., “BZ”) using transport theory to link cosmic ray fluctuations with IMF fluctuations (Bieber et al. 2013) REFERENCES Bieber, J. W., and P. Evenson, CME geometry in relation to cosmic ray anisotropy, Geophys. Res. Lett., 25, 2955-2958, 1998. Bieber, J. W., W. H. Matthaeus, C. W. Smith, W. Wanner, M.-B. Kallenrode, and G. Wibberenz, Proton and electron mean free paths: The Palmer consensus revisited, Astrophys. J., 420, 294-306, 1994. Bieber, J. W., P. Evenson, W. Dröge, R. Pyle, D. Ruffolo, M. Rujiwarodom, P. Tooprakai, and T. Khumlumlert, Spaceship Earth observations of the Easter 2001 solar particle event, Astrophys. J. (Lett.), 601, L103-L106, 2004. Bieber, J. W., J. Clem, P. Evenson, R. Pyle, D. Ruffolo, and A. Sáiz, Relativistic solar neutrons and protons on 28 October 2003, Geophys. Res. Lett., 32, L03S02, doi:10.1029/2004GL021492, 2005. Bieber, J. W., P. A. Evenson, T. Kuwabara, and C. Pei, IMF prediction with cosmic rays, Am. Geophys. Union Fall Meeting, abstract SH53A-2146, 2013. Chupp, E. L., H. Debrunner, E. Flückiger, D. J. Forrest, F. Golliez, G. Kanbach, W. T. Vestrand, J. Cooper, and G. Share, Solar neutron emissivity during the large flare on 1982 June 3, Astrophys. J., 318, 913-925, 1987. Dvornikov, V. M., V. E. Stobnov, and A. V. Sergeev, Analysis of cosmic ray pitch-angle anisotropy during the Forbush-effect in June 1972 by the method of spectrographic global survey, Proc. 18th Internat. Cosmic Ray Conf. (Bangalore), 3, 249-252, 1983. Kuwabara, T., J. W. Bieber, J. Clem, P. Evenson, R. Pyle, K. Munakata, S. Yasue, C. Kato, S. Akahane, M. Koyama, Z. Fujii, M. L. Duldig, J. E. Humble, M. R. Silva, N. B. Trivedi, W. D. Gonzalez, and N. J. Schuch, Real-Time cosmic ray monitoring system for space weather, Space Weather, 4, S08001, 2006a. Kuwabara, T., J. W. Bieber, J. Clem, P. Evenson, and R. Pyle, Development of a GLE alarm system based upon neutron monitors, Space Weather, 4, S10001, 2006b. Leerungnavarat, K., D. Ruffolo, and J. W. Bieber, Loss cone precursors to Forbush decreases and advance warning of space weather effects, Astrophys. J., 593, 587-596, 2003. H. Mavromichalaki and 33 co-authors, Applications and usage of the real-time neutron monitor database, Adv. Space Res., 47, 2210-2222, 2011. Oh, S. Y., J. W. Bieber, J. Clem, P. Evenson, R. Pyle, Y. Yi, and Y.-K. Kim, South Pole neutron monitor forecasting of solar proton radiation intensity, Space Weather, 10, S05004, 2012. Oh, S., J. W. Bieber, P. Evenson, J. Clem, Y. Yi, and Y. Kim, Record neutron monitor counting rates from Galactic cosmic rays, J. Geophys. Res., 118, 5431-5436, 2013. Palmer, I. D., Transport coefficients of low-energy cosmic rays in interplanetary space, Rev. Geophys. Space Phys., 20, 335-351, 1982. Pomerantz, M. A., and S. P. Duggal, The cosmic ray solar diurnal anisotropy, Space Sci. Rev., 12, 75-130, 1971. Richardson, I. G., V. M. Dvornikov, V. E. Sdobnov, and H. V. Cane, Bidirectional particle flows at cosmic ray and lower (~1 MeV) energies and their association with interplanetary coronal mass ejections/ejecta, J. Geophys. Res., 105, 12579-12592, 2000. Shea, M. A., D. F. Smart, and K. R. Pyle, Direct solar neutrons detected by neutron monitors on 24 May 1990, Geophys. Res. Lett., 18, 1655-1658, 1991. Souvatzoglou, G., H. Mavromichalaki, C. Sarlanis, G. Mariatos, A. Belov, E. Eroshenko, and V. Yanke, Real-time GLE alert in the ANMODAP center for December 13, 2006, Adv. Space Res., 43, 728-734, 2009. Tylka, A. J., and W. F. Dietrich, A new and comprehensive analysis of proton spectra in Ground-Level Enhanced (GLE) solar particle events, Proc. 31st Internat. Cosmic Ray Conf. (Lodz), Paper 0273, 4 pp., 2009. Directory: ~clem -> NMworkshop2015 -> paper paper -> Journal: The Astrophysical Journal paper -> Executive Summary Chapter 1 Introduction History, heritage and operation Download 163.4 Kb. Share with your friends:
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