Spectral Measurements of Direct Solar Radiation and of Sun's Aureole (II)

- Near Infrared Region -

Abstract

A new instrument improved in some points was constructed. Using this instrument measurements of direct solar radiation and au r e o l e intensity were performed. From the measurements of direct solar radiation, the spectral distribution of optical thickness of aerosol particles was obtained for each measurement. The spectral distributions obtained are classified into three types. The size distribution of aerosol particles corresponding to each spectral distribution of optical thickness is inferred for each measurement, by comparing with the theoretical calculations by FOITZIK and DEIRMENDJIAN. The size distribution inferred is the power law distribution with a hollow in the shorter side and a hump in the longer side of the range of radius. The wavelength region corresponding to the hollow and th e hump are dependent on the type of spectral distribution of optical thickness. Intensities of aureole at angular distance θ smaller than 5 deg. from the sun increase with increasing wavelength and those for θ>10 deg. are flat or slightly decrease with increasing wavelength. The ratio of monochromatic aureole intensity to that of the Rayleigh atmosphere increases with increasing turbidity factor T(λ)=[τ-M(λ)+τ R(λ)]τR(λ). The slopes of angular distributions of aureolein tensities corresponding to the three types of τM(2) are different from each othe rand the slope for type I is the largest among them. The dependency of slopes of the angular distributions on wavelength widely varies for each measure-. ment. The relation between the angular distribution and the siz e d i stribution of aerosol particles were also investigated by using the two in dices, that is, F= τM(0.4μ)/τM(0.8μ)-M(0.8μ)/τM(1.6μ)andAD=Iγ(1.5μ,θ)/γ(0.4μ,θ).