The Land-Ocean Contrast in Deep Convective Intensity in a Global Storm-Resolving Model

Observations reveal a clear difference in the intensity of deep convection over tropical land and ocean. This observed land-ocean contrast provides a natural benchmark for evaluating the fidelity of global storm-resolving models (GSRMs; global models with horizontal resolution on the order of kilometers), and GSRMs provide a potentially valuable tool for probing unresolved scientific questions about the origin of the observed land-ocean contrast. However, land-ocean differences in convective intensity have received relatively little attention in GSRM research. Here, we show that the strength of the land-ocean contrast simulated by GSRMs is strongly sensitive to details of GSRM implementations, and not clearly governed by any of several hypothesized drivers of the observed land-ocean contrast. We first examine DYAMOND Summer GSRM simulations, and show that only a subset produce a clear land-ocean contrast in the frequency of strong updrafts. We then show that the use of a sub-grid shallow convection scheme can determine whether or not the GSRM X-SHiELD produces a clear land-ocean contrast. Finally, we show that three putative drivers of the observed land-ocean contrast (convective available potential energy, boundary layer depth, and microphysics) fail to explain why a land-ocean contrast is present in X-SHiELD simulations with sub-grid shallow convection disabled. These results provide encouraging evidence that GSRMs can mimic the observed land-ocean convective intensity contrast. However, they also show that their ability to do so can be sensitive to uncertain sub-grid parameterizations, and suggest that existing theory may not fully capture drivers of the land-ocean contrast simulated by some GSRMs.