Variation of galactic cosmic rays near earth equator based on selected neutron monitors

摘要

Razaksat-1 is Malaysia's second remote sensing satellite that orbits at altitude of 685 km and at 9° inclination. A year after its launch, communication to the satellite was lost. Hence, this study is part of a research aimed to investigate whether space radiation is the cause behind its failure by focusing on the variation of galactic cosmic ray (GCRs) particles within the equatorial region. Study on GCR was based on real measurements taken in three years period (14 July 2009–14 July 2012) from selected neutron monitors (NM) in four different regions with satellite data from Cosmic Ray Isotope Spectrometer (CRIS) onboard Advanced Composition Explorer (ACE). The regions included North/East, North/West, South/East and the South Pole. The NM represented them were respectively Princess Sirindhorn NM (PSNM), Newark NM, Kingston NM and South Pole NM. Results showed that PSNM, as being the closest to the equator, had the highest neutron counts but the lowest cosmic ray variations in comparison with those at the higher latitude. There was a sudden neutron drop in March 2012 where no GCR flux was detected by ACE/CRIS for 10 days. More ACE/CRIS data were absent in certain times in 2011 and 2012. Comparison with OMNI data revealed that there was an increase of solar activity during these times. Prior to communication loss, it is found that solar protons are not responsible for the loss while high neutron peaks were detected in late 2009 to early 2010, indicating possible GCRs influence.