A parameterized neutron monitor yield function for space weather applications

To determine the characteristics of galactic or solar cosmic ray flux near Earth by using neutron monitor measurements, the observation data must be converted by extensive calculations that are addi- tionally burdened with inaccuracies (e.g. correction to sea level). However, for space weather applications a straightforward, fast, and possibly simple method is needed to allow data analysis in near real-time. The Geant4 simulation toolkit offers the possibility to simulate the interactions of cosmic ray particles with the atmosphere and the neutron monitor by the Monte Carlo method and therefore to determine the yield function of a specific neutron monitor in function of atmospheric depth and primary particle rigidity. The paper presents the results of such simulations for a NM64 monitor and includes a comparison with previ- ously determined yield functions. The new yield function is parameterized and can therefore be adapted to a neutron monitor at any location. The value and the use of the new yield function are demonstrated with the analysis of the neutron monitor data of the worldwide network during the maximum phase of the ground level enhancement on December 13, 2006.