TURBULENCE STRUCTURE IN CONVECTIVE BOUNDARY-LAYER

Results from a boundary layer experiment conducted over a flat site in northwestern Minnesota are discussed. Wind and temperature fluctuations near the ground were measured with fast-response instrumentation on a 32 m tower. Measurements between 32 m and the inversion base z//i were made with probes attached at five different heights to the tethering cable of a 1300 m**3 kite balloon. The daytime convective boundary layer appears to be well-mixed with evidence of significant heat and momentum entrainment through the capping inversion. The spectra of velocity components are generalized within the framework of mixed-layer similarity. The behavior of the temperature spectra above 0. 1z//i cannot be generalized in the same manner. Below that height the theta spectra follow behavior observed in the surface layer; z equals 0. 1z//i is also the upper limit for the free convection predictions of the w and theta variances. The high-order moments and the structure parameters reveal the strong influence of entrainment at heights above 0. 5z//i.