Forbush decreases detected at the Princess Sirindhorn Neutron monitor in the 24th Solar Cycle

Abstract

Neutron monitors (NMs) are ground-based detectors designed to measure the cosmic ray (CR) intensity by measuring secondary particles. A Forbush decrease (FD) is a sudden decrease in the CR-intensity count rate and the amplitude of the decreases changes with the different cutoff rigidity of each NM station. The Princess Sirindhorn NM (PSNM) was established in 2007, an NM64-type and 3 bare tubes located at the world’s highest geomagnetic vertical cutoff rigidity 16.8 GV was installed at Doi Inthanon in Thailand, 2565 m above sea level. In this work, we study the FDs in CR intensity detected at PSNM that occurred during the 5 years of 2010-2015 in the 24th solar cycle. We analyse the FDs at the Oulu NM in Finland in order to identify and compare them. We identify 46 FDs at both PSNM and Oulu NMs then we used the student’s t-test to assess difference in the mean between simultaneous or non-simultaneous of FDs event. We found that the 46 FDs, 22 are simultaneous and 24 non-simultaneous. Furthermore, we also found that student’s t-test analysis reveals that FDs at PSNM have smaller intensity variation of main phase duration of main phase than at Oulu NM. The results of the present statistical analysis that support the PSNM can provide CR data of reliability comparable to that of the Oulu NM. This work also provides unique data of FDs and solar modulation.