大気中の微粒子を考慮したモンテカルロ法による昼光散乱の空間分布解析

雲における昼光散乱の数値シミュレーション

抄録

This Monte Carlo simulation of the sky luminance and the daylight illuminance showed that
(1) when the sky is overspread with cloud whose properties are equal in the horizontal direction, the sky luminance is close to the CIE standard overcast sky luminance as the optical thickness of cloud increases. Then, if the sky luminance Lm is expressed as a function of the clear sky luminance Lc and the overcast sky luminance L_o, that is, L_m=e^-A×τL_c+ (1-e^-A×τ) Lo (where τ is the optical thickness), the coefficient A will become 0.16-0.28 when the sun altitude is 30-60 degrees. On the other hand, if the daylight illuminance Sr is expressed as S_r =S_o^-B × τthe coefficient B will become 0.012-0.027. And if the sky is darkly overcast, the optical thickness of the cloud becomes 52-32 when the sun altitude is 30-60 degrees.
(2) when the sky condition is the intermediate sky whose clouds are scattered, the sky luminance L_m is calculated as L_m= (1-C/10) L_c+ (C/10) {e^-A×τ L_c+ (1-e^-A×τ) L_o} (where C is the total cloud amount) if the average distribution of the cloud amount in the sky is constant. In the case of the daylight illuminance, the average value decreases with the increase of the total cloud amount but the maximum value and the minimum value do not necessarily decrease.