A new reconstruction of the heliospheric modulation potential for galactic cosmic rays is presented for the neutron monitor era, since 1951. The new reconstruction is based on an updated methodology in comparison to previous reconstructions: (1) the use of the new‐generation neutron monitor yield function; (2) the use of the new model of the local interstellar spectrum, employing in particular direct data from the distant missions; and (3) the calibration of the neutron monitor responses to direct measurements of the cosmic ray spectrum performed by the Payload for Antimatter Matter Exploration and Light‐nuclei Astrophysics (PAMELA) spaceborne spectrometer over 47 time intervals during 2006–2010. The reconstruction is based on data from six standard NM64‐type neutron monitors (Apatity, Inuvik, Kergulen, Moscow, Newark, and Oulu) since 1965 and two International Geophysical Year‐type ground‐based detectors (Climax and Mount Washington) for 1951–1964. The new reconstruction, along with the estimated uncertainties is tabulated in the paper. The presented series forms a benchmark record of the cosmic ray variability (in the energy range between 1 and 30 GeV) for the last 60 years and can be used in long‐term studies in the fields of solar, heliospheric, and solar‐terrestrial physics.

An updated yield function (YF) for a standard NM64 neutron monitor (NM) is computed and extended to different atmospheric depths from sea level to 500 g/cm² (~5.7 km altitude) and is presented as look‐up tables and a full parametrization. The YF was validated using the cosmic‐ray spectra directly measured in space by the AMS‐02 experiment during the period May 2011 through May 2017 and confronted with count rates of all NM64‐type NMs being in operation during this period. Using this approach, stability of all the selected NMs was analyzed for the period 2011–2017. Most of NMs appear very stable and suitable for studies of long‐term solar modulation of cosmic rays. However, some NMs suffer from instabilities like trends, apparent jumps or strong seasonal waves in the count rates.

Nearly 70 Ground Level Enhancements (GLEs) of cosmic rays have been recorded by the worldwide neutron monitor network since the 1950s depicting a big variety of energy spectra of solar energetic particles (SEP). Here we studied a statistical relation between the event-integrated intensity of GLEs (calculated as count-rate relative excess, averaged over all available polar neutron monitors, and expressed in percent-hours) and the hardness of the solar particle energy spectra. For each event the integral omnidirectional event-integrated fluences of particles with energy above 30 MeV ($F_{30}$) and above 200 MeV ($F_{200}$) were computed using the reconstructed spectra, and the ratio between the two fluences was considered as a simple index of the event's hardness. We also provided a justification of the spectrum estimate in the form of the Band-function, using direct PAMELA data for GLE 71 (17-May-2012). We found that, while there is no clear relation between the intensity and the hardness for weak events, all strong events with the intensity greater 100 \%*hr are characterized by a very hard spectrum. This implies that a hard spectrum can be securely assumed for all extreme GLE events, e.g., those studied using cosmogenic isotope data in the past.Comment: Advances in Space Research (in press

Neutron monitors provide continuous measurements of secondary nucleonic particles produced in the atmosphere by the primary cosmic rays and form the main tool to study the heliospheric modulation of cosmic rays. In order to study cosmic rays using the world network of neutron monitor and needs to be able to model the neutron monitor count rate. Earlier it was difficult because of the poorly known yield function, which has been essentially revisited recently. We have presented a verification of the new yield function of the standard neutron monitor (NM) using a recently released data on the direct in situ measurements of the galactic cosmic rays energy spectrum during 2006–2009 (the period of the record high cosmic ray flux) by Payload for Antimatter Matter Exploration and Light‐nuclei Astrophysics spaceborne spectrometer, and on NM latitude surveys performed during the period of 1994–2007, including periods of high solar activity. We found a very good agreement between the measured count rates of sea level NMs and the modeled ones in very different conditions: from low to high solar activity and from polar to tropical regions. This implies that the count rate of a sea level neutron monitor can be properly modeled in all conditions, using the new yield function.