Exploring the diurnal cycle in rainfall using idealized cloud resolving model studies

The diurnal cycle in tropical rainfall is a major mode of variability in our climate system, which we presently have an incomplete understanding of. Observations show that statistically, the diurnal rainfall maximum over land occurs 4-5 hours after local noon. In contrast, in large-scale numerical models, deep convection often erupts earlier in the day. It has been suggested that this is due the incorrect representation of moisture-convection relationships in numerical models.

In this study, I examine the results of simple experiments using a cloud resolving model, the System for Atmospheric Modeling (SAM), which are designed to study the diurnal cycle of deep convection over a tropical island in a highly idealized setting. Results show that including interactions with the ``large-scale dynamics'' that are often externally specified in cloud resolving model studies is crucial to reproducing the correct timing of the diurnal precipitation maximum. I discuss the reason for this result and the implications for how moisture is modulating deep convection in this context.