Updated Neutron-Monitor Yield Function: Bridging Between In Situ and Ground-Based Cosmic Ray Measurements

An updated yield function for a standard NM64 neutron monitor (NM) is computed and extended to different atmospheric depths from sea level to 500 g/cm(2) (similar to 5.7 km altitude) and is presented as lookup tables and a full parametrization. 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, 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.