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The Madden-Julian Oscillation (MJO) is a coupled air-sea interaction that dominates intraseasonal variability in the tropical oceans. This mode of variability is especially important in the tropical western Pacific Ocean warm pool because this region contains the warmest sea surface temperatures (SST), largest annual precipitation, and largest latent heat release in the atmosphere, which strongly affect the global redistribution of heat, moisture, and momentum. The MJO is difficult to reproduce in models, and some speculate it is because of the relationship between the MJO and diurnal SST variability (e.g. Zheng et al. 2004). A single-column coupled atmosphere-ocean model (SCCM) is used to calculate and evaluate the effects of diurnal SST variability on the marine boundary layer and convection during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE) Intensive Observations Period (IOP). Results show that the use of a diurnally-varying SST as opposed to a daily-averaged SST impact the lower atmosphere by several degrees and the upper atmosphere through convection. Large-scale advective tendencies of air temperature and specific humidity can act to enhance or reduce the effects of local feedbacks resulting from diurnal warming. The absence of the diurnal SST cycle substantially impacts the transition phases of the MJO with considerable differences in low-level and mid-level cloud amount, due to changes in low-level moistening, which is essential in preconditioning the atmosphere for deep convection. These results support the hypothesis that a lack of diurnal SST variability in large-scale models could contribute to incorrect moistening during the transition phase, which is important to simulating the MJO.