Conditional analysis of an internal boundary layer

Data from a convective internal boundary layer (IBL) are analyzed by focusing on the instantaneous structure of the top of the IBL instead of the time-average structure. A conditional averaging technique is developed to discriminate between air from above the IBL and air from below the IBL, which alternately invade some instrument levels due to substantial variation of the top of the convective IBL. Sensitivity to the conditional sampling criteria is examined. Inside the IBL, buoyant and mechanical production and dissipation dominate the turbulent kinetic energy budget. The horizontal advection and turbulent transport terms are smaller, but not negligible. The inferred pressure correlation term is negligible. Above the IBL, buoyant production and dissipation, although weak, dominate the turbulent kinetic energy budget. Shear generation and turbulent transport are smaller but significant.