FLUX DETERMINATION OVER A SMOOTH SURFACE UNDER STRONGLY UNSTABLE CONDITIONS

Careful micrometeorological measurements on an empty parking lot allowed determination of the surface fluxes of sensible heat H and of momentum by applying profile equations derived from Monin-Obukhov similarity theory with two sets of the stability correction function for momentum Psi(m) and sensible heat Psi(h). These fluxes were compared with reference values of H independently determined by means of an eddy correlation technique. In general, better agreement was found between H values derived from profiles with the stability functions of Brutsaert (1992) and reference H values, than when the Businger-Dyer functions were used to derive H. The disagreement in the latter comparison was especially serious under strongly unstable conditions, with the value of y = -z/L (where z is the height and L is the Obukhov length) larger than 10. A closer look at the procedure for calculating H from the profiles revealed that the large differences between the H values derived with these two different versions of the stability correction functions were caused by the small differences of the Psi(h) values, and not by the larger differences of the Psi(m) values. This result stems from the strong sensitivity of the resulting H values on the choice of Psi(h).