Abstract Radiosonde data from the JA SIN meteorological triangle, of sides 200 km, have been used to construct mean budgets of mass, momentum and sensible and latent heat. Typically the atmospheric boundary layer (bl) consisted of a near-neutral subcloud layer and a conditionally unstable cloud layer beneath an inversion. Clouds were cumulus under a stratocumulus layer. W ind shears within the bl were small and the mean vertical motion at the bl top was less than 1 pbar s-1||. Acceleration terms were of similar order (10-4 m s-2) to the geostrophic departure, and significant stress within the cloud layer implied convective momentum transport. The latent heat flux dominated the sub-grid-scale vertical heat transfer, being on average nearly constant from the surface to the cloud-layer top. The results emphasize the importance of cloud processes in determining boundary layer structure.