Hosted by: Stephen Schwartz

Fractional cloudiness in climate models is parameterised in terms of the subgrid-scale variability of humidity. This variability is expressed explicitly or implicitly as the probability density function (PDF) of the total-water specific humidity. No large-scale high-resolved observations of water vapour exist. I will present four approaches to evaluate the humidity PDF despite this observational shortcoming, and show their application to evaluate different cloud schemes. I will then discuss the implications for other cloud processes, and the subsequent improvements within the ECHAM climate model. If time permits, I will also briefly summarise one recent study on an observational constraint on the aerosol radiative forcing.