Statistical analysis of the connection between galactic cosmic rays and atmospheric and land climate variables.

By ionizing the air, Galactic Cosmic Rays (GCR) help to form aerosols that may grow into cloud condensation nuclei (CCN), which are required for water droplets to condense and create low-altitude clouds with a consequent cooling effect on the Earth's climate. This communication investigates the indirect effect of GCRs on different atmospheric variables. The parameters used in the analysis are GCR flux, sunspot number (SSN), geomagnetic (AA) index, $CO_2$, $CH_4$, cloud liquid water path, cloud effective radiation, aerosol optical depth (AOD), and Earth radiation budget as the predictor variables and near surface temperature as the response variable. Monthly means of GCR count rates from two neutron monitors (NM), one at mid-latitude (Newark, New York) and another at high-latitude (Oulu), are employed along with in situ (ICOS/FLUXNET for $CO_2$ and $CH_4$, BSRN/SURFAD for radiation), ground-based (AERONET for AOD), and satellite (for cloud properties) measurements. Linear and multiple linear regression models, including collinearity, are used for the analysis. The correlation between GCR and leaf area index (LAI) is also discussed, but to indirect effects that GCRs may have on soil and vegetation.