Given that the diurnal cycle is a forced mode of variability, it is surprising that only limited efforts have been made to improve its representation in global climate models. The diurnal cycle of precipitation and clouds is important since it influences radiative heating and surface fluxes; all of which may be poorly represented in GCMs. Additionally, the diurnal cycle is important since it influences low-level jets, modulates the moisture and heat budgets over land and ocean, and the phasing and amplitude of rainfall over regions of complex orography. Recent evidence has indicated that the diurnal cycle of convection rectifies onto longer time scales of variability suggesting that its adequate simulation is necessary for the representation of multi-scale interactions.

The diurnal cycle of rainfall and surface fluxes is evaluated in simulations performed as part of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Emphasis will be on the diurnal cycle over ocean and land in the vicinity of the tropical monsoons. Where possible, the influence of the diurnal cycle on the simulation of the Madden-Julian Oscillation will be explored. Time permitting the behavior of the diurnal cycle in the climate change simulations will also be evaluated.