A New Heat Flux Formulation Based on Effective Surface Temperatures, With Extension to the Nocturnal Boundary Layer

Abstract

Abstract : The state of the art concepts of the influence of surface heterogeneity on the atmospheric boundary layer are studied using several new data sets. This analysis shows that the internal boundary layer theory is valid only with sharp well defined surface changes. With more typical surface heterogeneity and with very stable conditions, the concept and models of the internal boundary layer do not apply. The concepts of the thermal roughness length and aerodynamic variables are also found to fail, or behave in an undeterminable complex manner, over both modest and strong surface heterogeneity including microscale heterogeneity associated with complex vegetation and tall partially open canopies. Generalized formulations and new approaches are suggested. With very stable conditions, similarity theory breaks down and the concept of the boundary layer is challenged. The primary source of the turbulence may originate from elevated semi-detached shear layers and surface based similarity theory fails to describe even the flux gradient relationship near the surface. While we have modified similarity theory to better parameterize surface fluxes in very stable conditions, major uncertainties remain.