A new method for determining atmospheric pressure coefficient using fast Fourier transform for muons in the GRAPES-3 experiment

Abstract

A large area (560 m2) tracking muon detector operating in the GRAPES-3 experiment at Ooty in India has been recording cosmic ray muons at a rate of 1.7× 108 h-1 since 2000. The high statistics data have enabled sensitive measurements of several solar phenomena to be made including the solar and sidereal anisotropy and Forbush decreases associated with coronal mass ejections. Prior to studying of any of these phenomena, an important task is to correct the variation in measured muon rates due to atmospheric pressure. Unfortunately, the pressure coefficient usually deduced from the observed data is not very reliable due to the presence of various solar phenomena listed above. Here, we present an alternative method which avoids complications arising from solar effects. Since the pressure at Ooty displays a 12 h periodicity, using which we could separate its contribution from other effects in the muon data though a power spectrum analysis. The method yielded a clear dependence of muon rate on pressure providing an accurate estimate of the pressure coefficient almost independent of the solar modulation effects.