On the Non-monotonic Variation of the Entrainment Buoyancy Flux with Wind Shear

Abstract The magnitude of the entrainment buoyancy flux, and hence growth rate convective boundary layer, does not increase monotonically with wind shear. Explanations for this have previously been based on wind-shear effects turbulence kinetic energy. By distinguishing between turbulent non-turbulent regions, we provide an alternative explanation two competing effects: initial decrease in correlation vertical velocity fluctuations, area fraction. former is determined by change dominant forcing; without shear, fluctuations drive are thus highly correlated; partly horizontal via transfer energy through pressure–strain correlation, reducing their field. increasing fraction, other hand, shear production inside zone. We also show that dependence these conditional statistics boundary-layer depth can be captured a single non-dimensional variable, which interpreted as entrainment-zone Froude number.