Sensible Heat Fluxes in the Nearly Neutral Boundary Layer: The Impact of Frictional Heating

In nearly neutral conditions at high wind speeds apparently anomalous behavior of the sensible heat flux has sometimes been observed. Mahrt et al., 2012, J. Phys. Ocenaogr., 42, pp. 1134-1142, report observations of upward heat fluxes at high wind speeds when the surface is slightly colder than the air above and discuss some possible explanations. Smedman et al., 2007, Q. J. Roy. Meteorol. Soc., 133, pp. 227-250, suggest that heat transfer is enhanced by the presence of roll vortices in slightly unstable conditions. Here, it is suggested that frictional heating between the surface and the height at which fluxes are measured should be taken into account in such cases, and that it can give rise to measurements of countergradient heat fluxes and apparently enhanced surface transfer. The effect can be represented by small modification of the bulk flux formula. The impact of this modification on theoretical models of tropical storms will be discussed and results from simulations of a hurricane, carried out using a high-resolution nested configuration of a general circulation model will be presented.