Moroccan weather and climate are influenced by desert winds coming from South-East and by Atlantic advections. The annual cycle of seasonal average of aerosol optical depht shows similar values in Oujda and Saada and registers higher values in Ouarzazate, due to different weather conditions. The maximum values are recorded in summer near 0.25 (Oujda, Saada) and 0.34 (Ouarzazate). The seasonal average of the refraction index varies with the seasons, the component relating to scattering at 0.44 microns varies lightly in summer (1.48 -1.51) and the component relating to absorption varies (6.65×10 -3 -13.13×10 -3 ) with more higher values in Oujda. The single scattering albedo is almost constant for every season and indicates a very important trend in the diffusion which often exceeds 89% in summer. The asymmetry factors seem constant close 0.73 in summer indicating more forward scatter. The volume distributions show a mode of very fine particles around 0.015 μm and a much more important mode of large particles around 2.6 μm (annual average) that registers large amplitudes in spring and especially in summer (seasons penetration of desert dust across all regions by the advection of air masses mainly from Southeast Morocco). The annual average radiative forcing are relatively stable around -25.34 W/m 2 to bottom and -4 W/m 2 at the top of the atmosphere.

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Atmospheric aerosol is an important factor that affects solar irradiance. In this study, we examined the total atmospheric optical depth, aerosol optical depth AOD and the vertical particle size distribution in East Asia in terms of aerosol type during three years. The temporal variation of the aerosol optical depth for each site showed a constant mode renewed each year, the large AOD0,5 are recorded in spring and summer in an almost periodic manner, with maximums around 0.95 in Seoul, 0.08 in Chiang Mai and 1.34 in EPA-NCU. The particle size distributions under a bimodal lognormal form present a remarkable increase in volume concentration of fine and coarse modes during spring. The aerosols reduce solar irradiance by 37.33 ± 0.78% in Chiang Mai, 33.48 ± 6.43% in EPA-NCU and 38.59 ± 3.86% in Seoul.

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