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On the size dependence of cumulus cloud spacing
  • Thirza van Laar,
  • Roel A J Neggers
Thirza van Laar
Helmholtz-Zentrum Geesthacht

Corresponding Author:thirza.vanlaar@gmail.com

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Roel A J Neggers
University of Cologne
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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.