On the Appropriate Scaling for Velocity and Temperature in the Planetary Boundary Layer

Abstract

Data from a recent experiment indicate that the height scale for wind in the planetary boundary layer is u_*/F, where u_*/F is the friction velocity and f the Coriolis parameter, rather than z_i, the height of the convection-limiting inversion, or |L| the Obukhov length. None of the scales u_*/f, z_i, |L| appears to be appropriate for temperature except in slight-to-moderate stability where again u_*/f appears to be the most suitable. The data do not support either Businger's expression which gives the depth of the idealized thermal boundary layer, depending on surface heat flux and rate of temperature change, or Tennekes' expression for bulk temperature difference across the boundary layer in free convection, based on the ratio of −L to the roughness length z₀.