Behavior of Turbulence Statistics in the Convective Boundary Layer

Abstract

Velocity variances in the convective boundary layer are examined using data derived in PBL experiments over land (Minnesota) and ocean (the Coral Sea) supported by data from the Kansas study of the surface boundary layer. In the freely convective limit, the data clearly support scaling of σ_w by the convective Velocity w_* instead of u_*, as is common in modern treatments. The freely convective limit appears to be 0.59 for both σ_w/w_* and σ_v/w_*. The available data are compatible with relationships based on additive contributions to total variance by mechanical and buoyant forces. The resulting relations areThese relations collapse back to the neutral values derived from the Kansas experiment. Similar analyses for temperature variance are somewhat less revealing; however, the available data indicate that scaling by convective properties alone is quite adequate. Hence,where θ_* = H/ρc_pw_*. These relations appear to apply over the bulk of the convective PBL, from z/z_i ≈ 0.1 to at least z/z_i = 0.6, but extend downwards to very near the surface in the case of σ_v