The Temperature Effect in Secondary Cosmic Rays (Muons) Observed at the Ground: Analysis of the Global Muon Detector Network Data

Abstract

The analysis of cosmic ray intensity variation seen by muon detectors at Earthʼs surface can help us to understand astrophysical, solar, interplanetary and geomagnetic phenomena. However, before comparing cosmic ray intensity variations with extraterrestrial phenomena, it is necessary to take into account atmospheric effects such as the temperature effect. In this work, we analyzed this effect on the Global Muon Detector Network (GMDN), which is composed of four ground-based detectors, two in the northern hemisphere and two in the southern hemisphere. In general, we found a higher temperature influence on detectors located in the northern hemisphere. Besides that, we noticed that the seasonal temperature variation observed at the ground and at the altitude of maximum muon production are in antiphase for all GMDN locations (low-latitude regions). In this way, contrary to what is expected in high-latitude regions, the ground muon intensity decrease occurring during summertime would be related to both parts of the temperature effect (the negative and the positive). We analyzed several methods to describe the temperature effect on cosmic ray intensity. We found that the mass weighted method is the one that best reproduces the seasonal cosmic ray variation observed by the GMDN detectors and allows the highest correlation with long-term variation of the cosmic ray intensity seen by neutron monitors.

Analysis of Cosmic Rays' Atmospheric Effects and Their Relationships to Cutoff Rigidity and Zenith Angle Using Global Muon Detector Network Data

“…Considering barometric effect theory, see, for example, Sagisaka () or Appendix A of de Mendonça, Braga, Echer, Dal Lago, et al (), we define the atmospheric pressure effect on the muon count rate as where I [ x , y ] ( t ) is the cosmic ray count rate observed in directional channel at the [ x , y ] position at time t ; P ( t ), given in hectopascals, is the ground atmospheric pressure measured on the detector site at the same time; 〈 I [ x , y ] 〉 and 〈 P 〉 are both reference values (in this work, the mean values of I [ x , y ] ( t ) and P ( t ) obtained in the period of analysis, respectively); and β [ x , y ] is the barometric coefficient in percent per hectopascal representing how much the pressure effect influences the observed cosmic ray intensity. Hereinafter, the β [ x , y ] will only be denoted by β .…”

“…Considering barometric effect theory, see, for example, Sagisaka (1986) or Appendix A of de Mendonça, Braga, Echer, Dal Lago, et al (2016), we define the atmospheric pressure effect on the muon count rate as…”

“…In this work, we use 3-hourly atmospheric temperature profiles obtained for every 1°-by-1°surface grid around each GMDN site and scaled in 24 fixed atmospheric pressure levels. Following de Mendonça, Braga, Echer, Dal Lago, et al (2016) results, we adopt the mass-weighted method to describe the temperature effect. In this way, we compile the atmospheric temperature profiles in single variable as shown below:…”

Effects of ICMEs on High Energetic Particles as Observed by the Global Muon Detector Network (GMDN)

“…They produce a seasonal variation on the cosmic ray intensity observed by muon detectors. We recommend a careful reading of De Mendonca et al (2016) for details on corrections of GMDN observations for atmospheric effects. Perhaps the most well known modulation that ICMEs impose in ground cosmic rays is the Forbush decrease (Forbush 1937;Simpson 1954).…”

High-energy cosmic ray modulation associated with interplanetary shocks observed by the GMDN

“…As for the temperature effect, we adopted the mass weighted method (see, e.g., [16] and [17]. We have chosen this method because it was found to be the best to remove the temperature effects on the GMDN data among several other methods available [18]. We used the temperature profiles extracted from the Global Data Assimilation System (GDAS).…”