Gregory, D., et al., 2000: Revision of convection, radiation and cloud schemes in the ECMWF Integrated Forecasting System. (ipcc.ch)
Both Haywood and Ramaswamy (1998) and Penner et al. (1998b) acknowledge that their use of on / off cloud schemes where cloud fills an entire grid box once a threshold relative humidity is exceeded may lead to strong radiative forcings due to strong non-linear relative humidity effects. (ipcc.ch)
In - depth analysis reveals that the model's shallow cumulus convection scheme tends to significantly under - produce clouds during the times when shallow cumuli exist in the observations, while the deep convective and stratiform cloud schemes significantly over-produce low - level clouds throughout the day. (pubs.giss.nasa.gov)