Barometric coefficient dependence on the geomagnetic cutoff rigidity of neutron monitors

Several studies have been showing that cosmic ray intensity variations observed at the Earth surface can be a useful tool to analyze and predict space weather and climate phenomena. However, before reach the ground level, the cosmic ray particles interact with different atmospheric atoms. This results in the generation of different secondary particles that are differently affected by atmospheric effects. For example, data from neutron monitors, which are widely used to study cosmic ray flux changes related to space phenomena, are significantly affected by atmospheric pressure changes. Thus, for a more detailed study of these instruments’ data, it is necessary to know very well how works the pressure affects secondary neutrons. In this way, we seek to understand how this effect changes according to the cosmic rays’ energy. Thus, in this work, we compare how the barometric coefficient (β), which quantifies the pressure effect on the cosmic ray intensity, changes with the geomagnetic cutoff rigidity (RC), which quantifies the minimal rigidity/energy that a primary particle needs to reach a given location in a chosen direction. To do that, we used data recorded between January 2008 to December 2016 by several neutron monitors around the globe with RC from 0.1 to 8.3 GV. We experimentally obtained β in two ways: (I) the typical one, which does not explicitly consider isotropic variations unrelated to the pressure effect; and (II) one that considers such variations by using coupling coefficients and a reference neutron monitor station. Like other works, we found that the pressure effect seems to present a logarithmic relation with the cutoff rigidity when we estimate β through the typical method used. On the other hand, we found that the pressure effect linearly decreases with the cutoff rigidity when considering an adjustment in this typical method to eliminate external isotropic variations. This linear relation appears to not change accordingly to the reference monitor chosen. These results enhance our knowledge of how the pressure effect globally acts on the cosmic ray intensity observed at ground level and, consequently, improves future analysis about global changes in the cosmic ray flux related to space weather phenomena.