| 5 | 5 | This project used PALM simulations to investigate how the turbulent structure of the atmospheric boundary layer is influenced by small scale surface inhomogeneities with typical diameters of about the boundary layer height z,,i,,. The inhomogeneities were designed as discontinuous, chessboard-like variations of the surface heat flux that was prescribed as the bottom boundary condition. A large heat flux amplitude was chosen to create conditions typical of the Arctic or Antarctic marginal ice zone during cold air outbreaks. One main aim of this study was to determine the effects of such large heat flux variations and to describe the influence exerted by variations of incident flow speed and direction. Particular interest was paid to the inhomogeneity-induced secondary circulations that were analyzed using phase averages. \\\\ |
| 6 | 6 | Compared with continuous inhomogeneities of the same size, discontinous inhomogeneities principally cause similar, but much stronger effects. In contrast to a homogeneously heated boundary layer the horizontally averaged second and third moments are considerably affected by the inhomogeneities. Significant effects, however, only occur when the diameter of the inhomogeneities is at least as large as the height of the boundary layer. Then, especially the vertical energy transport increases, and the effects of the inhomogeneities start to show up even in the vertical temperature and heat flux profiles that don't exhibit the shapes typical of a homogeneous CBL any longer. The vertical gradient of potential temperature is slightly positive within the entire mixing layer, and the heat flux profile departs from its usual linear shape. These changes, though, are not due to the discontinuous form of the inhomogeneities but mainly due to the large heat flux amplitude. \\\\ |
