Temperature effect correction for the cosmic ray muon data observed at the Brazilian Southern Space Observatory in São Martinho da Serra

Abstract

The negative atmospheric temperature effect observed in the muon intensity measured by surface-level detectors is related to the atmospheric expansion during summer periods. According the first explanation given, the path of muons from the higher atmospheric level (where they are generated) to the ground becomes longer, and more muons decay, leading to a muon intensity decrease. A significant negative correlation, therefore, is expected between the altitude of the equi-pressure surface and the muon intensity. We compared measurements of the altitude of 100 hPa equi-pressure surface and data from the multidirectional muon detector installed at the Brazilian Southern Space Observatory in São Martinho da Serra, RS. Significant correlation coefficient were found (up to 0.95) when using data observed in 2008. For comparison, data from the multidirectional muon detector of Nagoya, located in the opposite hemisphere, is studied and an anti-phase in the cosmic ray variation related with the temperature effect is expected between data from detectors of Nagoya and São Martinho da Serra. The temperature influence is higher for the directional channels of Nagoya than for ones of São Martinho da Serra.

Atmospheric- Weighted Temperature and its influence on Cosmic Ray muons

“…While the strength of this relation between the two parameters is different from one year to another, the association is obvious throughout all years. These results are consistent with those previously found for different experiments [4,[7][8]. 3shows the monthly variations of the measured muon rate versus the (a) T wd and (b) T ww .…”

“…Although the barometric effect correction, in which atmospheric pressure at the detector level needs to be known [5], is simple, the temperature effect is rather difficult and needs to be determined by the overall profile of the temperature at all altitudes of the atmosphere. The effect of the atmospheric temperature on the muon count rate is usually studied by considering the temperature and/or the height of the pion production level [6][7][8][9][10]. On the other hand, the integrated temperature of an isothermal atmosphere with its varying conditions is sometimes calculated to study the influence of the atmospheric temperature on the detected muons.…”

Correlation between Cosmic Ray muons and atmospheric temperature in the lower stratosphere

“…The correlation between the two variables implies that the parent pions will have less probability of decay to produce muons before they interact as the temperature decreases (winter), while the opposite is the case during warm seasons (summer). This result is in agreement with those previously reported [7][8][9]. The interannual variations of the mean monthly values of the raw and temperature corrected muon rates, for the considered time period, are presented in Figure 5.…”

“…Correlation between Cosmic Ray muons and atmospheric temperature in the lower stratosphere The relative variations of cosmic ray muons due to the effects of atmospheric pressure and temperature is described as [7][8][9]:…”

“…On the other hand, the temperature corrections are slightly more complicated and several methods have been suggested to account for them [e.g., 1 and 3]. These include correlation of the muon rates with one of the following parameters: the atmospheric weighted temperature [4][5], the temperature at ground level [3 and 6], or with the temperature at the level of pion production [7][8][9][10][11].…”