A new way of understanding and predicting nocturnal wind bursts
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The project aims to solve a long-standing problem in boundary layer meteorology: to find the physical mechanism that drives intermittent (discontinuous) turbulence in the nocturnal boundary layer. During intermittency, periods with ?laminar? flow are interrupted by chaotic bursts of turbulence and a significant transport of heat, moisture and momentum occurs. Bursts also act as an efficient ?venting?-mechanism of pollutants that usually accumulate in quiet periods. The problem is highly relevant in weather and climate prediction and for air pollution problems. Current nocturnal boundary layer parameterizations are highly empirical and lead to significant errors in weather and climate predictions. Besides the intermittent boundary layer two other prototypes exist: the ?radiative? (laminar) boundary layer and the well-understood continuous turbulent (windy) boundary layer. The key innovative aspect lies in our hypothesis: we hypothesize that both intermittent and radiative boundary layers are natural physical instabilities of the continuous turbulent boundary layer, which cannot maintain its turbulence when the large-scale pressure force is too small. As such, we will show that all three prototypes can be described within a single physical framework: a ground-breaking result! In our approach we combine our mathematical analysis with advanced numerical modelling of turbulence (so-called: direct numerical simulation). A fundamentally new aspect is the fact that in our theoretical analysis we incorporate the important nonlinear atmosphere-surface feedbacks explicitly. This aspect was disregarded in the past. We aim to come up with a predictive theory for the regime-transitions mentioned above, so that weather and climate model will have a solid physical basis on this aspect. Finally, the theoretical predictions are compared with two well documented datasets (the CASES99 field experiment dataset, Kansas, U.S.A.; KNMI-Cabauw dataset, Netherlands). The grant applies for the applicant plus a PhD. Keywords: STABLE BOUNDARY LAYER, REGIMES, INTERMITTENCY
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