Cloud Ensemble Simulation with Data from the Atmospheric Radiation Measurement Intensive Observation Period

The main objective of this study is to use Atmospheric Radiation Measurement (ARM) intensive observation period (IOP) data to refine a cloudiness parameterization, as proposed by Xu and Randall (1996a). The cloudiness parameterization uses the large-scale average condensate (cloud water and cloud ice) mixing ratio as the primary predictor. The large-scale relative humidity and cumulus mass flux are also used in the parameterization as secondary predictors. The cloud amount is assumed to vary exponentially with the largescale average condensate mixing ratio. The rate of variation is, however, a function of large-scale relative humidity and the intensity of convective circulations. In the version of the parameterization presented by Xu and Randall (1996a), the intensity of convective circulations was yet to be included; that is, only the condensate mixing ratio and large-scale relative humidity were used as predictors.