The effect of heterogeneous surface temperature and aerodynamic surface roughness on fluxes in the stable boundary layer

Natural land surface heterogeneity typically entails simultaneous changes in multiple surface properties. Here, we examine how the stable boundary layer (SBL) is affected by concurrent transitions in surface temperature and aerodynamic surface roughness. Both hot-rough-to-cold-smooth and cold-rough-to-hot-smooth transitions are considered using velocity and potential temperature fields generated from large-eddy simulations. Particular attention is focused on determining the importance of the correlation between surface roughness and surface temperature on the dynamics of the boundary layer. For the cold-rough-to-hot-smooth case, the cold-rough patch dominates the boundary layer leading to decreased boundary layer height and enhanced average negative heat fluxes in the boundary layer in comparison to equivalent cases with only surface temperature or surface roughness heterogeneity. The opposite effect occurs for the hot-rough-to-cold-smooth case leading to increased boundary layer height and decreased in magnitude boundary layer fluxes. The dominance of the hot-rough patch leads to a decoupling between the boundary layer heat flux and the vertical gradient of potential temperature at scales on the order of the heterogeneous patch length. This has important implications for the application of gradient based turbulent flux models in heterogeneous SBLs.