Direct numerical simulation of laminarization in the atmospheric boundary layer

A well-known phenomenon in the atmospheric boundary layer is the facts that winds may become very weak in the evening after a clear sunny day. In these quiet conditions usually hardly any turbulence is present. Consequently, this type of boundary layer is referred to as the quasi-laminar boundary layer. In spite of its omnipresence, the appearance of the laminar boundary layer is poorly understood and forms a long-standing problem in meteorological research. In the present study we investigate an analogue problem in the form of a stably stratified channel flow. The flow is studied by using direct numerical simulations (DNS). Simulations reveal that flow laminarization occurs when the normalized surface heat extraction h/L is larger than 1.23. In a companioning study this laminarisation is explained by the maximum sustainable heat flux theory (MSHF), which will be validated in the present research.