The variability and seasonality in the ratio of photosynthetically active radiation to solar radiation: A simple empirical model of the ratio

•We developed a simple empirical model to estimate the ratio of PAR to solar radiation.•We demonstrated the global distribution of the ratio ranged from 0.41 to 0.48.•The ratio was lower in high latitudes and the inland and higher in low latitudes and the coast.•We also demonstrated the seasonal change of the ratio around the world.•The model accuracy was relatively low in snow season and aerosol-dense atmosphere.