A study of probability distributions of boundary‐layer humidity and associated errors in parametrized cloud‐fraction

摘要: Observations of boundary-layer-humidity probability-distributions made with the Meteorological Office tethered-balloon facility have been derived from nine representative days between 1996 and 1999. Measurements include those at several heights simultaneously. Four types distribution defined, including skewed multimodal types. These analysed on scales relevant to sub-grid parametrizations. functions fitted observations their accuracy in predicting cloud fraction assessed. It was found that a standard beta-type gave best representation observed humidity-distribution. In addition, it for grid greater than about 5 km, advection plays significant role determining form humidity distribution, this must be accounted any The cloud-fraction error arising errors mean total specific-humidity saturation is also discussed. That former relatively large.