Physics
Scientific paper
Jul 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003icrc....7.3901a&link_type=abstract
Proceedings of the 28th International Cosmic Ray Conference. July 31-August 7, 2003. Trukuba, Japan. Under the auspices of the I
Physics
Scientific paper
The widely used concept of the neutron monitor energy range is not well defined. Also, the median energy of a neutron monitor varies in the course of the solar cycle. Here we present a new concept of the effective energy of cosmic rays measured by neutron monitors. Using a 1D model of the heliospheric transport of cosmic rays and the specific yield function of a neutron monitor, we show that there is such an energy value, here called the effective energy, that the count rate of a given neutron monitor is directly proportional to the flux of cosmic rays with energy above this effective energy, irresp ective of the phase of the solar cycle. The new concept of the effective energy allows to regard the count rate of each neutron monitor as a direct measurement of the galactic cosmic ray flux with energy above the effective energy specified for tha station. The effective energy varies from about 5.5 GeV for polar up to about 20 GeV for equatorial stations. The effective energy for the cosmogenic polar 10 Be and global 14 C production is about 1.3 GeV and 2.8 GeV, respectively. The data of the world-wide network of neutron monitors (NMs) provide a good, stable and consistent data set of galactic cosmic ray (GCR) intensities for more than 50 years. However, a NM is an integral device measuring all cosmic rays above a certain energy (local geomagnetic or atmospheric rigidity cutoff ) with the yield function increasing sharply with energy. Therefore, it is not clear what is the effective energy of cosmic rays as measured by NM. In this paper, we intro duce a concept of the effective energy of a NM, Eef f , so that the count rate of a given neutron monitor is directly proportional to the flux of cosmic rays with energy above this effective energy, irresp ectively of the phase of solar cycle. In other words, variations of NM count rate directly corresp ond to variations of the GCR flux above this effective energy. Neutron monitor count rates can be obtained as follows: ∞ G(T , t) · Y (T , x) · dT N (Pc , x, t) = (1) Pc
Alanko K. M.
Kovaltsov Gennadi A.
Mursula Kalevi
Usoskin Ilya G.
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