Explorations in understanding the diurnal rainfall cycle over islands

Observations show that statistically, the diurnal rainfall maximum over land occurs 3-5 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 tropical islands in highly idealized settings. 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.