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[1] The error in the diurnal cycle of precipitation over land in the tropics in the European Centre for Medium-Range Weather Forecasts forecast model is investigated using a single column model with idealized forcing of the omega field, as well as short-term and long runs of the full three-dimensional model. The model precipitates a few hours after sunrise, as it does not represent correctly the morning development of a growing cumulus boundary layer. In the single column model, precipitation is closely linked to the mean forcing and surface evaporation, but the phase of diurnal varying omega forcing in relation to the diurnal solar cycle determines the relation of convective to large-scale precipitation in the control model, as well as cloudiness and the net radiation balance. With diurnal subsidence peaking at midnight, but no mean ascent, the model shows a quasi 2-day precipitation mode. With both strong mean ascent and diurnal forcing, ascent peaking in the daytime gave stratiform rain with large cloud cover and very low surface net radiation, while daytime subsidence and ascent at night gave strong daytime convective precipitation and high net radiation

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