Questions and comments may be directed to: ncei.info@noaa.gov
There are many possible mechanisms that can accelerate particles up to the CR range of energy. When the acceleration process is associated with solar flares and/or Coronal Mass Ejections (CMEs), the CR particles released to the interplanetary medium are called Solar Cosmic Rays (SCRs) or Solar Energetic Particles (SEPs). This phenomenon can cause Solar Radiation Storms (measured, studied and categorized by NOAA). The flux and composition of SEPs is strongly variable; energies are generally below 1 GeV, rarely reaching 10 GeV.
CR Flux
The CRs with energies above 10 GeV measured near Earth originate from outside of the Solar System, either in our Galaxy or outside of it. These are called Galactic Cosmic Rays (GCRs). Both GCR and SEP compositions have a major contribution of fully ionized protons and alpha-particles with a smaller, but important, contribution of heavier nuclei.
Since the primary CR flux is composed of charged particles, it is expected that any magnetic irregularity and/or turbulence affects their large-scale transport and consequently their energy spectrum. Through its journey to Earth, the CR flux is modulated inside the Heliosphere by the Interplanetary Magnetic Field (IMF) and solar wind conditions, which vary according to the Solar Cycle Progression. Near Earth, the CR fluxes are almost isotropic but the CR particle’s trajectories will be affected by Lorentz forces due to the geomagnetic field. This results in a latitudinal-dependency from their interaction with our atmosphere. The portion of the CR spectrum that reaches the Earth's atmosphere is controlled by the geomagnetic cutoff which varies from a minimum (theoretically zero) at the magnetic poles, to a vertical cosmic ray cutoff of about 15 GV (ranging from 13 to 17) in the equatorial regions. (Note, a GeV is a unit of energy, and GV is a unit of magnetic rigidity.)
Using ground-based, or underground detectors, or deploying balloons for sounding, different devices can be used to measure each component of the CR’s cascade from underground to high altitude. The near ground measurements of the flux of secondary CR particles from the cascade provides information concerning the different modulation processes suffered by the primary CR during their transport in the heliosphere, magnetosphere and atmosphere, and also the journey of the secondary CR particle. This is why CR particles are considered “Celestial Messengers.”
Neutron Monitors
In order to detect the nucleonic component at the Earth’s surface, a proportional gas-filled counter called a Neutron Monitor (NM) is used. The International Geophysical Year (IGY), in 1957, and the International Quiet Sun Year (IQSY), in 1964, marked the implementation of a global network of standardized NM stations.
Today, most of the data from past and current worldwide NM stations can be found at the Neutron Monitor Database website (NMDB) and at WDC-CR : World Data Center for Cosmic Rays, Geospace Research Center, Solar-Terrestrial Environment Laboratory, Nagoya University.
Forbush Decrease and GLEs
Forbush Decreases are abrupt decreases of the background galactic cosmic ray intensity as observed near ground typically by neutron monitors. They are associated with major plasma and magnetic field enhancements in the solar wind at or beyond the Earth. These magnetic field enhancements deflect the background CR particles. GLEs are sharp increases in the ground-level CR count to at least 10 percent above background, associated with solar protons of energies greater than 500 MeV. GLEs are relatively rare, occurring only a few times each solar cycle. When they occur, GLEs begin a few minutes after flare maximum and last for tens of minutes to hours. Intense particle fluxes at lower energies can be expected to follow this initial burst of relativistic particles.
Annals of The Geophysical Year (IGY) (1957-1959) Volumes XXVI, XXVII and XXVIII (26, 27, and 28), Editor J.A. Simpson, CSAGI Reporter for Cosmic Rays.
Bihourly (2h) cosmic ray databases:
- Neutron Monitor (46 stations)
- Cubical Telescope (38 stations)
- Vertical Telescope (2 stations)
- Ion Chamber (16 stations)
- Shower Apparatus (1 station) data monitored during the July 1957-December 1959 IGY and International Geophysical Cooperation (IGC) time period (Read Me).
- Explanation of the IGY Data Tables: NOTE These cosmic ray data are published in three volumes of the Annals of the IGY. Data was stored on 5 1/4 inch floppy diskettes and converted in 2005 to more recent storage media. Originally they were stored on punched cards. Not all station data published in the Annals have been found.
Neutron Monitor Data -- hourly, daily and monthly averages from a worldwide network 1953-2015 (documentation).
- NM Cosmic Ray Tabulated Observations (1996-2011)The table presents the daily (UT) average counting rates per hour (scaled) for seven high counting rate neutron monitors: Thule, Deep River, Kiel, Climax, Beijing, Tokyo, and Haleakala. The characteristics of the stations and the barometric coefficients used to correct the data can be found at the read me file.
- NM Cosmic Ray Observations from 4 Bartol stations(1957-2012) - Yearly files with average counting rates per hour for four high counting rate neutron monitors of the Bartol Research Institute (BRI): McMurdo, Swarthmore/Newark, South Pole and Thule. Today, the Bartol Research Institute operates 10 NM stations. Updated datasets are provided at the BARTOL NEUTRON MONITORS website.
- NM Cosmic Ray from WDCCR stations (1953 until 2015) - Cosmic-ray neutron fluxes (pressure-corrected and level-adjusted) taken by a global network of neutron monitors. Data provided by the World Data Center for Cosmic Rays (WDCCR) at Nagoya University’s Solar-Terrestrial Environment Laboratory as a part of the activities of the Climate and Weather of the Sun-Earth System-II (CAWSES-II) program under the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP), International Council for Science (ICSU). The database includes corrected 1-hour values and plots of monthly averages. The basic data format employed by the WDCCR was the 4096-byte LONGFORMAT, which can be sorted by the name of a station or a certain year. Since data in this format are compact but relatively inconvenient to handle, WDCCR also provided the SHORTFORMAT in which 12 hourly data were given in one line, instead of "one month data in one line" in the LONGFORMAT. The SHORTFORMAT data can be sorted by the yearly base.
- Updated data from WDCCR stations can be found at WDC-CR : World Data Center for Cosmic Rays, Geospace Research Center, Solar-Terrestrial Environment Laboratory, Nagoya University portal. (read me)
- Forbush Decrease list from Mt. Washington Observatory (1955-1996) Archived lists of Forbush Decrease events (1955-1996) from Mt. Washington Observatory (N44.30 E288.70; Cut-off Rigidity = 1.24 GV; Altitude 1900 m) – Table of YYMMDD and percent decrease of daily averages (less than 3% are not included) of Forbush Decreases from Mt. Washington.
- Cosmic Ray Ground Level Enhancements (GLEs) (1942-2001) GLE list compiled by M.A. Shea (formerly with AFRL) and D.F. Smart updated until 2012 and provided by the Australian Antarctic Division. The list includes the event number (1 to 65), event date, and some information about the baseline data used to determine the magnitude of the event.
- Today, the official database of Neutron Monitor count rates during GLE events is https://gle.oulu.fi/.
- Cosmic Ray ionization chambers data from Carnegie Institute of Washington (1936-1968) – pdf scans of legacy bi-hourly ionization chamber data from the stations Huancayo, Cheltenham/Fredericksburg, Christchurch, Godhavn and Mexico that was operated under the supervision of Dr. S.E. Forbush and transferred to NCEI (formerly National Geophysical Data Center). The documentation of the NGDC digitization project and results are also available here.