Influence of stability on the flux-profile relationships for wind speed, φ_m, and temperature, φ_h, for the stable atmospheric boundary layer

Abstract

Data from SABLES98 experimental campaign have been used in order to study the influence of stability (from weak to strong stratification) on the flux-profile relationships for momentum, φ_m, and heat, φ_h. Measurements from 14 thermocouples and 3 sonic anemometers at three levels (5.8, 13.5 and 32 m) for the period from 10 to 28 September 1998 were analysed using the framework of the local-scaling approach (Nieuwstadt, 1984a; 1984b), which can be interpreted as an extension of the Monin-Obukhov similarity theory (Obukhov, 1946). The results show increasing values of φ_m and φ_h with increasing stability parameter ζ=z/3, up to a value of ζ≈1–2, above which the values remain constant. As a consequence of this levelling off in φm and φh for strong stability, the turbulent mixing is underestimated when linear similarity functions (Businger et al., 1971) are used to calculate surface fluxes of momentum and heat. On the other hand when φ_m and φ_h are related to the gradient Richardson number, R_i , a different behaviour is found, which could indicate that the transfer of momentum is greater than that of heat for high R_i . The range of validity of these linear functions is discussed in terms of the physical aspects of turbulent intermittent mixing.