A study on observed evolution of boundary layer humidity distributions

Data are used from the Met Office tethered balloon facility to examine the evolution of boundary layer humidity probability density functions during various meteorological conditions. Results typically show significant changes in all four moments (mean, standard deviation, skewness and kurtosis) over periods from one to several hours. Boundary layers experiencing the greatest changes were normally convective in nature. In contrast, a quiescent wintertime boundary layer was seen to show very little evolution over a period of two days. Models which use statistical distributions of humidity for cloud prediction should ideally be able to reproduce these observations.