This paper presents the results of a boundary layer experiment conducted over a flat site in northwestern Minnesota, focusing on the turbulence structure in the convective boundary layer. The experiment utilized fast-response instrumentation on a 32-meter tower and MRU probes attached to a 1300 cubic meter kite balloon to measure wind and temperature fluctuations. The convective boundary layer was found to be well-mixed, with significant heat and momentum entrainment through the capping inversion. The spectra of velocity components were analyzed within the framework of mixed-layer similarity. The characteristic wavelength for the vertical velocity \( w \) increased linearly up to \( 0.1 z_i \) and approached a limiting value of 1.5\( z_i \) in the upper half of the boundary layer. The characteristic wavelengths for horizontal velocities \( u \) and \( v \) remained at approximately 1.5\( z_i \) down to heights close to the ground. This limiting wavelength corresponds to the length scale of large convective elements extending to the top of the boundary layer. The temperature spectra above \( 0.1 z_i \) could not be generalized in the same manner. Below this height, the spectra followed behavior observed in the surface layer, with \( z = 0.1 z_i \) being the upper limit for free convection predictions of the variance of \( w \) and \( \theta \). High-order moments and structure parameters revealed the strong influence of entrainment at heights above 0.5\( z_i \). The behavior of the temperature spectra and the stress profiles provided insights into the momentum transport process, with large stresses observed near \( 0.5 z_i \) and decreasing above this height. The largest contributions to the stress cospectra came from frequencies in the energy-containing region, indicating that most vertical momentum transport occurs within the updraft regions of longitudinal roll vortices.This paper presents the results of a boundary layer experiment conducted over a flat site in northwestern Minnesota, focusing on the turbulence structure in the convective boundary layer. The experiment utilized fast-response instrumentation on a 32-meter tower and MRU probes attached to a 1300 cubic meter kite balloon to measure wind and temperature fluctuations. The convective boundary layer was found to be well-mixed, with significant heat and momentum entrainment through the capping inversion. The spectra of velocity components were analyzed within the framework of mixed-layer similarity. The characteristic wavelength for the vertical velocity \( w \) increased linearly up to \( 0.1 z_i \) and approached a limiting value of 1.5\( z_i \) in the upper half of the boundary layer. The characteristic wavelengths for horizontal velocities \( u \) and \( v \) remained at approximately 1.5\( z_i \) down to heights close to the ground. This limiting wavelength corresponds to the length scale of large convective elements extending to the top of the boundary layer. The temperature spectra above \( 0.1 z_i \) could not be generalized in the same manner. Below this height, the spectra followed behavior observed in the surface layer, with \( z = 0.1 z_i \) being the upper limit for free convection predictions of the variance of \( w \) and \( \theta \). High-order moments and structure parameters revealed the strong influence of entrainment at heights above 0.5\( z_i \). The behavior of the temperature spectra and the stress profiles provided insights into the momentum transport process, with large stresses observed near \( 0.5 z_i \) and decreasing above this height. The largest contributions to the stress cospectra came from frequencies in the energy-containing region, indicating that most vertical momentum transport occurs within the updraft regions of longitudinal roll vortices.