Shear Capacity as prognostic of nocturnal boundary layer regimesetc15 Tracking Number 32 Presentation: Session: Atmospheric turbulence 1 Room: Room C Session start: 10:30 Tue 25 Aug 2015 Ivo van Hooijdonk i.g.s.v.hooijdonk@tue.nl Affifliation: Eindhoven University of Technology Judith Donda j.m.m.donda@tue.nl Affifliation: Eindhoven University of Technology Fred Bosveld fred.bosveld@knmi.nl Affifliation: KNMI Arnold Moene arnold.moene@wur.nl Affifliation: Wageningen University Herman Clercx H.J.H.clercx@tue.nl Affifliation: Eindhoven University of Technology Bas van de Wiel b.j.h.v.wiel@tue.nl Affifliation: Eindhoven University of Technology Topics: - Atmospheric turbulence Abstract: In some nights, the near-surface temperature can drop dramatically and turbulence in the stably stratified boundary layer becomes very weak, such that the lfow reaches a (quasi-) laminar state. In other cases, however, the atmosphere remains in a turbulent state and temperatures stay relatively high. Recently, the appearance of two distinct boundary layer regimes was explained by a new theoretical framework. This theory builds on the fact that the turbulent heat flux in stably stratified flow is limited to a maximum for given wind shear. This introduces a characteristic flux-based velocity scale, which can be used to predict the regimes. This hypothesis is consistent with field observations and numerical results. Also, the hypothesis is generalised to a dimensionless framework. |