On the relationship between interception of direct solar radiation by cactus bodies and plant leaves

Abstract

The interception of direct solar radiation by cactus bodies is calculated by computation of the average of the cosine of the angle of incidence over the surface of two models: a cylindrical model with a horizontal top and a prolate or oblate ellipsoidal model. An expression is obtained for the fraction of maximum possible solar radiation intercepted by a particular surface element for fixed values of the zenith angle of the sun. This expression is averaged by numerical integration over the surface of the cactus body to yield the average cosine of angle of incidence. The resulting relationships between cosine of angle of incidence and solar zenith angle show significant differences with respect to similar relationships for flat leaves. However, if a correction is applied for attenuation of direct solar radiation by the atmosphere, differences are greatly reduced.