A STOCHASTIC DESCRIPTION OF A BROKEN CLOUD FIELD

The chord length distributions within a cloud and between clouds are c onsidered. Such information is needed as input to certain statistical models of cloud-radiation interaction. Modeling the clouds as azimutha lly symmetric ellipsoids, the authors find that the chord length distr ibution through a cloud of fixed size is proportional to the chord len gth. The proportionality constant depends upon the semiaxes of the ell ipse as well as the angle of incidence of the radiation. This linear b ehavior is easily convolved over an arbitrary size distribution of the clouds to obtain the chord length distribution through a statistical mixture of different cloud sizes. The chord length distribution betwee n clouds is also considered for an atmospheric layer of finite thickne ss. In this case, both analytic and numerical methods are needed to ob tain results. In the limit of an infinite thickness atmospheric layer described by homogeneous statistics and fixed cloud chord lengths, our considerations reduce to a Markovian (exponentially distributed chord lengths) model for the intercloud spacing.