Heat Flux in Strong Wind and Unsteady Weak-Wind Stable Boundary Layers

The behavior of the downward surface heat flux in the stable boundary layer is examined for the entire range of wind speeds using data from FLOSS, SCP and 14 other supplementary field programs. For weak-wind conditions, the unsteadiness of the flow significantly augments the heat flux beyond that predicted by similarity theory. The unsteadiness of the heat flux and temperature profile is compared with that for the momentum flux and wind field.

With strong turbulence, small changes of the weak stratification produce large variations of the heat flux. Significant stratification with stronger winds appears to be maintained by warm air advection, as inferred from the tower heat budget and auxilliary analyses, although other causes are not ruled out. For most of the sites, the largest downward heat fluxes are found with strong winds even though the corresponding z/L corresponds to near neutral conditions. These cases are analyzed in detail.