A lead (a break in the Arctic ice) allows contact between the warm ocean and the cold atmosphere. Because of its importance for the energy budget of the atmosphere many numerical simulations have been made so far to get detailed information about the vertical heat flux and the atmospheric turbulence induced by leads. Nevertheless, the spatial resolution of these simulations is still too coarse to resolve the turbulence directly above the lead, where the convective boundary layer (CBL) may increase to maximum heights of only a few meters. Whereas in the past spatial resolution was restricted due to insufficient hardware resources, today high-performance computer architectures allow significant increases in model resolution. In this study a large-eddy simulation model developed for a massively parallel computer is used to show that an increased model resolution leads to significant changes in the simulation results, which are in contrast with earlier studies of flows above and on the leeward side of a single lead. The better the model resolution is, the earlier the convection starts, and this affects the overall CBL structure. Organized roll-like structures on the downstream side of the leads that appeared in earlier studies are shown to be completely caused by insufficient grid resolution. The effect of model resolution on the simulation results becomes even greater for higher wind speeds because with increasing geostrophic wind speed (and mean wind speed) the boundary layer depth decreases and an even finer grid becomes necessary. ¿ 2001 American Geophysical Union