CONTEXT

The diurnal cycle of convection over land is of major importance for many aspects of climate studies, in particular  via its strong modulation of the radiative budget by convective clouds and its control on surface temperature. For instance, in summer, intense convection over land typically develops in a diurnal pattern forced by surface heating. At the same time, the diurnal cycle of convection, not yet properly captured by existing numerical climate and weather forecast models, appears as a well identified,  significant weakness of these models (Figure 1).

Figure1: Seasonal mean phase of the diurnal harmonic in precipitation for DJF and JJA (local time given) based on (a) satellite derived rainfall estimates and (b) from the UKMO Unified Model. The model reproduces a systematic error that many AGCMs exhibit, raining too early in the day. The seasonal means for Winter are based on the years 1984/85, 1986/87, 1987/88 and 1991/92. The seasonal means for summer are based on 1985, 1986,1987 and 1992 (Courtesy J. Slingo).