Early Warning Signals for Regime Transition in the Stable Boundary Layer: A Model Study

• Published in: Boundary-layer meteorology 2017-02, Vol.162 (2), p.283-306
• Main Authors: van Hooijdonk, I. G. S., Moene, A. F., Scheffer, M., Clercx, H. J. H., van de Wiel, B. J. H.
• Format: Article
• Language: English
• Subjects: Atmospheric boundary layer; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Boundaries; Boundary layer; Boundary layers; Computational fluid dynamics; Critical regime transition; Dynamical systems; Early warning signals; Earth and Environmental Science; Earth Sciences; Mathematical models; Maximum sustainable heat flux; Meteorology; Minimum wind speed; Nocturnal boundary layer; Numerical analysis; Research Article; Similarity; Simulation; Turbulence; Turbulent flow; Wind
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1007/s10546-016-0199-9

The evening transition is investigated in an idealized model for the nocturnal boundary layer. From earlier studies it is known that the nocturnal boundary layer may manifest itself in two distinct regimes, depending on the ambient synoptic conditions: strong-wind or overcast conditions typically lead to weakly stable, turbulent nights; clear-sky and weak-wind conditions, on the other hand, lead to very stable, weakly turbulent conditions. Previously, the dynamical behaviour near the transition between these regimes was investigated in an idealized setting, relying on Monin–Obukhov (MO) similarity to describe turbulent transport. Here, we investigate a similar set-up, using direct numerical simulation; in contrast to MO-based models, this type of simulation does not need to rely on turbulence closure assumptions. We show that previous predictions are verified, but now independent of turbulence parametrizations. Also, it appears that a regime shift to the very stable state is signaled in advance by specific changes in the dynamics of the turbulent boundary layer. Here, we show how these changes may be used to infer a quantitative estimate of the transition point from the weakly stable boundary layer to the very stable boundary layer. In addition, it is shown that the idealized, nocturnal boundary-layer system shares important similarities with generic non-linear dynamical systems that exhibit critical transitions. Therefore, the presence of other, generic early warning signals is tested as well. Indeed, indications are found that such signals are present in stably stratified turbulent flows.