How are the seasonal cycles of aerosols connected to climate zones?

Abstract:

Long term aerosol climatologies of ground based observations reveal that aerosol properties follow characteristic annual patterns. For example, northern European locations typically exhibit maxima of aerosol optical depth (AOD) in summer with a relatively high but little varying fine mode fraction. In dry subtropical locations the summer maximum is coinciding with a low fine mode fraction due to dust outbreaks. In subtropical or tropical savanna locations the dry season is marked with a significant increase of AOD and fine mode fraction due to biomass burning. Here we address the question of how these typical seasonal cycles are linked to the corresponding climate zones. Based on the Aerosol Robotic Network (AERONET) dataset of 136 stations worldwide with more than 7 years of observations, we characterize the average annual cycle of AOD and fine mode fraction of each station by fitting a Fourier series with two harmonics which reduces the description of the aerosol cycles to a low dimensional parameter space. Several statistical methods are applied to investigate the relationship of these characteristic aerosol parameters and the corresponding climate of each station. Climate classification according to Köppen and Geiger is used as well as precipitation and temperature climatologies. The results help understand the origin of the aerosol seasonal cycles and may have implications for the response of aerosols to shifting climate zones.