Neutron monitor altitude-dependent yield function and its application to an analysis of neutron-monitor data

An updated yield function (YF) of a standard NM64 neutron monitor (NM) is computed for different atmospheric depths from sea level to 500 g/cm(2) (similar to 5.7 km altitude) and is presented as a full parametrization. The NM YF was computed using the PLANETOCOSMICS simulation tool based on the GEANT4 package, applying the NRLMSISE-00 atmospheric model. The yield function 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, the stability of all 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.