Executive Summary Chapter 1 Introduction History, heritage and operation
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- STANDARD COSMIC RADIATION DATA FORMAT SUBMISSIONS TO WORLD DATA CENTERS DURING THE IGY
- Neutron Monitor Operations
- Neutron Monitor as a Primary Cosmic Ray Detector
Neutron Monitors in the IGY (Peggy)
The International Geophysical Year (IGY) from July 1957 to December 1958 provided a unique opportunity for scientists to conduct multi-discipline geophysical studies using data acquired from a large variety of sensors located around the world. One of the objectives of the IGY was the worldwide exchange of scientific data. To meet this objective the World Data Centers were established. These were established at places where there was scientific research in specific disciplines. Four World Data Centers for Cosmic Rays were established with Center A at the University of Minnesota. STANDARD COSMIC RADIATION DATA FORMAT SUBMISSIONS TO WORLD DATA CENTERS DURING THE IGY 
Standard Cosmic Radiation Data Format Submissions to World Data Centers during the IGY The initial plans for the exchange of cosmic radiation data during the IGY called for bi-hourly atmospheric pressure values and bi-hourly neutron monitor data corrected for atmospheric pressure. Special data forms were prepared for uniform reporting; these forms were to be sent to each cosmic ray data center every three months with a letter of data transmittal sent to the IGY Headquarters in Belgium. An example of a month of data is shown in Figure 1. The initial publication of the Carnegie ionization chamber data (Lange and Forbush, 1948) contained only bi-hourly data, and this may have influenced the IGY organizers in their initial planning. At the time of the IGY planning meetings, only four high energy solar proton events had been identified: two in 1942, 1946 and 1949, and the publication of those results contained graphs of bi-hourly ionization chamber data (Forbush 1946; Forbush et al., 1950). Relativistic solar proton events were considered so rare that no provision was made for the exchange of data in smaller time increments than the bi-hourly values. There were other factors to be considered. The scientific data prior to and during the IGY were primarily recorded on paper either handwritten or typed. Digital counters were installed at most sites with a camera recording the counters at set time intervals. After the film was developed, the digital values had to be manually read, and since the counters did not reset themselves at specified intervals, each reading had to be subtracted from the following value to obtain the counting rate within the specified period. The barometric pressure was usually recorded on analog charts with hourly values recorded by hand. Next the cosmic ray counting rate for the specified interval had to be corrected for the atmospheric pressure for that time period using a pre-determined barometric pressure coefficient appropriate for the station. Once the values were obtained, they had to be typed or hand written on the official IGY data forms. The entire process of recording the data was time consuming and laborious. As preparations were underway for reporting and archiving cosmic radiation data, a major solar proton event occurred on 23 February 1956. The neutron monitor at Leeds, UK recorded an increase of 4581% over a 15-minute period. The event was world-wide in scope with significant increases in the equatorial region indicating the presence of particles in excess of 15 GV at the top of the atmosphere. Sarabhai et al. (1956) estimated the maximum energy of solar protons to be >50 GeV. Plans were quickly revised to recommend recording intervals of 15 minutes (or less) so that unusual "events" would permit detailed post event analyses (Nicolet, 1959). The routine bi-hourly reporting intervals to the World Data Centers remained unchanged. The ground-level enhancement (GLE) of 23 February 1956 remains as the highest increase in 15 minute data recorded by neutron monitors. While there are higher increases for the 20 January 2005 GLE, these increases are for much shorter time intervals and were recorded at polar stations (Bieber et al., 2005). When averaged over a 15-minute interval, the percentage increase for the 20 January 2005 event is less than the increase at the Leeds neutron monitor on 23 February 1956. The GLE of 23 February 1956 is still actively studied today (Rishbeth et al., 2009). Many groups planning their neutron monitor data recordings for the IGY had already implemented plans for smaller time interval data with some groups installing "flare alarms" which increased the recording interval if there was a rapid increase in the counting rate. While the IGY was during one of the most active solar cycles, there were no ground-level solar cosmic ray events during this time interval. The shorter time interval data was, however, extremely useful in the study of Forbush decreases of which there were many. At the start of the IGY in July 1957 there were 43 IGY neutron monitors operating world wide. Nine of these monitors were in the USA; two others at Mexico City and Huancayo were under the auspices of the University of Chicago. (The Thule neutron monitor did not become operational until August 1957.) In December 1959, at the end of the International Geophysical Cooperation (the one year extension of the IGY) there were 58 IGY neutron monitors in operation around the world including the same nine monitors in the USA and those in Mexico City, Huancayo and Thule. During the IGY, in addition to submitting bi-hourly data to the World Data Centers, the scientists initiated an exchange of data amongst themselves. It was relatively common for one group involved in a specific study, to request detailed data from another group, and this cooperation was readily acknowledged in subsequent publications. In addition to the exchange of data within the cosmic ray community, other scientists conducting research on various solar and geomagnetic phenomena were utilizing cosmic radiation data as a baseline describing the cosmic ray intensity during periods of interest. The use of neutron monitor data, particularly from the Climax neutron monitor, greatly increased with the advent of the space era. Neutron Monitor Operations In most stations each proportional counter has a dedicated electronics interface that records the total number of pulses that occur above a pre-set threshold over different integration periods. A new generation of electronics recently developed by the Bartol Research Institute, also records the time between pulses. For further details of this instrumentation and its use for determining cosmic ray spectra, see Bieber et al. 2002. These systems are currently in operation at the Newark and Thailand stations. The average number of evaporated neutrons produced in an inelastic interaction is energy dependent and can be roughly described as a power law, consequently spectral information can be in principle extracted this timing data. The capabilities of this new system is describe in Chapter 2 of this paper. 
Figure 7. International Neutron Monitor station network linked to NMDB data servers Most of the US operating stations are fully automated with realtime data over internet or satellite connections. The data is transferred to the home database and the international Neutron Monitor Data Base (NMSB). The property for the station is leased and a local contact/observer is under contract for general building maintenance, technical support and snow removal. Instrumentation maintenance is currently operating on a “parts swap” basis such as electronic components, digital barometers, and GPS systems, however regular visits to remote stations have been discontinued due to lack of funding. Personnel directly associated with station operation are nominally a full-time, PhD-level data manager and for approximately halftime support for an Electronics Technician. Duties of the Electronics Technician include communications with remote observers, identifying and solving technical problems with station operation, and travel to the remote stations for maintenance and repair as needed. The nominal duties of the data manager include: station management, station data streaming, data processing, data quality control, data dissemination, data archiving, and maintenance of real-time data resources. This includes data transfer to the local database and to international Neutron Monitor database http://www.nmdb.eu/ Neutron monitors have been in operation for over sixty five 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). Great strides have been made in providing access to data, both archival and near-real-time, for researchers throughout the field of Space Science. Neutron monitor data, in particular, has for many decades enjoyed a unique history of world-wide collaborative efforts and the unrestricted sharing of datasets among researchers. This is in large part due to the nature of the measurements made by neutron monitors; an understanding of the time-varying, anisotropic galactic or solar cosmic ray spectrum in most cases requires that data from a large array of stations needs to be considered, and often that array must be global in scope. The main goals of the Neutron Monitor database (http://NMDB.eu) are to provide high-resolution data from all Neutron Monitor stations in a standard format,to provide real-time data, and to make it easily accessible for everyone. The standard data format has been implemented by storing the measurements in a SQL database. The stations are sending the data immediately after the measurement to NMDB, so that the data is available in real-time (ie less than 5 minute delay after the measurement where possible). The data is made available to everyone to an easy to use webinterface at http://nest.nmdb.eu where data can be plotted and downloaded in ASCII format. For real-time applications a direct read-access to the database is available. The database already contains data from over 50 stations, not only real-time measurements but also historical data. To allow all stations to provide real-time data affordable registration systems have been designed during the NMDB project, the designs are freely available to all interested users. Since the International Geophysical Year 1957, when a world-wide network of standard IGY neutron monitors was put in place, data from these stations and their successors has been, for the most part, freely shared among experimenters. Since each neutron monitor views the cosmic ray flux arriving from a relatively small range of directions, it was early recognized that, especially in the analysis of solar flare particle events, a network of stations, distributed in magnetic latitude and longitude, were necessary to characterize the flux of charged particles in nearby interplanetary space. Between 1956 and 1958 the number of international operating monitors grew from 8 to 52. A good number of these stations were active only during the IGY, and were then closed in the late 1950s. However, in 1964 the NM64 monitor was developed which provided a greatly-increased counting rate, and many of the operating stations were upgraded to this new design. The total number of operating stations (IGY and NM-64) reached a peak of 65 in 1964, then declined gradually to its current level of about 45 by the late 1970s. As for the US operated stations, the time profile and map is displayed in Figure XX 
Chapter 2 Cosmic-ray and Heliospheric Science
The energy distribution or spectrum of cosmic rays cannot be teased from the count rate of a single instrument. One must use several monitors for this purpose. Many modern applications use the network itself, and not any single monitor. The latitude and longitude distributions of stations allows studies of the cosmic-ray pitch angle distribution and momentum spectrum. The global array constitutes an enormous magnetic spectrometer, where the geomagnetic field sorts cosmic rays based on their momentum or energy with the rates from several monitors being used to piecewise assemble a spectrum responsible for the signal in all the instruments. The mathematical description of this process is described as follows: In reality, the process and physics is more complicated. One major complicating factor is that the cosmic rays in the Earth environment may not be isotropic, i.e., they come preferentially from a general direction in space, typically linked to the local direction of the interplanetary field. Consequently, cosmic-ray trajectories from this non-uniform distribution are also non-uniform as they map through the geomagnetic field to the ground and the various instruments. This anisotropy can be confused with the non-uniformity intrinsic to the energy response of the neutron monitor network. Disentangling these effects requires care and is especially important for energetic particles coming from the Sun, as we describe below. The original intent of neutron monitors was to measure these Sun-associated effects—some poorly recognized from pre-neutron monitor measurements. The zoo of solar effects can be stated concisely. They are (1) direct solar particles (SEPs) superimposed on the intensity of primary cosmic rays from the Galaxy, (2) solar-cycle modulation of the local intensity of galactic primary cosmic rays and (3) transients in the GCR intensity tied to singular events on the Sun. Below we discuss the progress made over the years in these areas enabled by neutron monitor measurements. 
Figure XX Neutron Monitor Count rate recorded on the Italian Antarctic Program 3-NM-64 survey during 1996–97 (Villoresi, 1997).  
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