In this study the spatial structure of Trade Wind shallow cumulus
populations is investigated as diagnosed from large-domain high
resolution cloud-resolving simulations. The main objective is to
establish how inter-cloud spacing depends on cloud size, information
that is crucial for understanding cloud-radiation interaction and
spatial organization, and for informing grey zone parametrizations. A
high-resolution cloud-resolving ICON simulation of Caribbean shallow
convective cloud fields is used, based on the NARVAL South field
campaign. The size statistics of the simulated cloud population are
found to compare well to those derived from available satellite images.
Four expressions for the nearest neighbor spacing are analyzed,
including classic definitions but also novel ones. We find that the
dependence of cloud spacing on cloud size strongly depends on this
definition. The relation is exponential for the spacing between clouds
of similar size, while it is logarithmic for the spacing between clouds
of any size. Further analysis suggests that the logarithmic dependence
is caused by the abundance of closely-spaced small clouds. The
exponential size-dependence is argued to reflect the mesoscale dynamics
driving the horizontal size of large convective cells. The implications
of the obtained results are briefly discussed.