Abstract
High energy cosmic ray (CR) particles are capable of ionizing the Earth's atmosphere, which lead to changes in the atmospheric properties that affect its physical and chemical characteristics. One of the most important results of the interactions between the CR particles and the atmospheric molecules is the formation of aerosol and its subsequent condensation processes. In this study, the relationship between the time series of the aerosol optical properties; namely the aerosol optical depth (AOD) and Angstrom exponent (α), and the CR muons and neutrons was investigated and established. AOD and α monthly mean data were obtained from the AERONET site located in central Saudi Arabia (24.91° N, 46.41° E, 760 m), for the period of 1999–2015 and the corresponding CR data from Oulu neutron monitor were used for these investigations. Cosmic ray data for the period of 2002–2012 obtained from KACST muon detector were also used in this study. Correlation analyses between the time series of CR data (measured by NM and muon detector) and the aerosol optical properties were carried out and showed significant correlations between these variables. While AOD was positively correlated with the CR data, α showed the opposite.
Power spectral analyses using Fast Fourier transform (FFT) were applied on the monthly mean time series of the considered variables to search for possible common periodicities between them. The results showed that there is similarity in position of at least one local peak in PSD (near 1.6–1.7 years) in α and in CR. The correlation and power spectral analyses indicate possible mutual relation between variations of aerosols observed at a particular site and CR intensity observed on the ground.
•The relationship between cosmic rays and aerosol optical properties were investigated and established.•Correlation analyses between CR and aerosol optical properties showed non-zero relationship between them.•The amount of the aerosol optical depth at 500 nm increases as the cosmic ray flux increases.•The size of the aerosols (α440-870) decreases as the number of the cosmic ray neutron increases.•Spectral analysis provides indication of presence of ~1.6 – 1.7 year quasi- periodicity in the signal of α440-870.•The correlation and power spectral analyses indicate possible mutual relation between variations of aerosols and CR intensity analyzed here.