Optical characterization of cloud and aerosol of the temperate zone

Abstract

Aerosol and cloud optical data of the network AERONET/PHOTONS are in major importance in climate change and air quality studies. Sun photometers allow the determination of cloud and aerosol optical depths and the particle size distribution of aerosol for many sites distributed over large four zones belongs to the temperate areas: Mediterranean, maritime, humid subtropical, and continental and dry. The histograms of cloud occurrence frequencies reveal the dominance variation in the interval (20.100) relating to Stratus and Altostratus, maximum reaches (~ 70%) recorded at eastern Asia (China). For values below 20, the histograms are different from those of Equatorial zone but modeled into two classes, staircase and non-staircase shapes, depending on the weather conditions. The monthly aerosol optical depth averages at 0.5 μm show the highest values in summer, a maximum reach 1.6 at Eastern Asia and coincides with the highest cloud optical depth particularly for Asian sites. Seasonal average of aerosol particle size distribution records larger amplitudes of both fine and coarse modes in the Asian sites especially in the East two to three times higher than those in other zones. The average radius of fine mode is around 0.17 μm expressing high anthropogenic local pollution. The coarse mode around 2.75 μm is very important in Western India with a maximum concentration in summer as seasonal desert dust advections concern.