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Project properties |
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| Title | What is the role of the interaction between the atmosphere and the surface temperature on the collapse and revival of turbulence in the stable boundary layer? |
| Group | Meteorology and Air Quality Group |
| Project type | thesis |
| Credits | 36 |
| Supervisor(s) | Arnold Moene (this work may be performed in conjunction with dr. Bas van de Wiel of Eindhoven University of Technology and/or Judith Donda). |
| Examiner(s) | Prof. dr. AAM Holtslag |
| Contact info | Arnold.Moene@wur.nl |
| Begin date | 2018/01/01 |
| End date | 2019/02/01 |
| Description | The main characteristic of the stable boundary layer is that buoyancy suppresses
turbulence. The delicate balance between turbulence production by shear and turbulence destruction by buoyancy determines the regime of turbulence in the nocturnal boundary layer. If the mechanical forcing is sufficiently strong, continuous turbulence will result, whereas under conditions with very weak mechanical forcing, turbulence will collapse completely. For intermediate wind speeds, the turbulence becomes intermittent: periods with sustained turbulence are mixed with periods of very weak turbulence. Van de Wiel et al. (2002a) developed an attractive conceptual model for this oscillatory behaviour. One of the key ingredients was the interaction between surface temperature (of a vegetation layer with small heat capacity) and the turbulence. Recently attempts have been made to simulate a similar system with a Direct Numerical Simulation (DNS) model (a model that explicitly computes turbulent motions albeit at low Reynolds numbers). It turned out that no intermittent behaviour was found. One of our conjectures is that this might be due to the fact that the characteristics of the vegetation layer restrict the timescales of interaction between surface temperature and atmosphere too much. Therefore we would like to extend our DNS model with a full soil model with sufficient resolution to cover all relevant time scales. The work involved in this project consists –among others– of the following tasks: • analyse available data sets to characterize the observed connection between atmospheric flow and the surface temperature. • extend an existing DNS model with a model for the soil temperature with a sufficient number of levels to represent variations on all relevant time scales. • define sets of parameter values that might lead to intermittent behaviour (based on van de Wiel et al. (2002b) where the difference between a single vegetation layer and a full soil temperature model should be taken into account. • make various runs and analyse the model results (study the development of turbulent kinetic energy as well as the dynamics of the surface temperature of the soil). References Wiel, B.J.H. van de; Ronda, R.J.; Moene, A.F.; DeBruin, H.A.R.; Holtslag, A.A.M. (2002a). Intermittent turbulence and oscillations in the stable boundary layer over land. Part I: A bulk model. Journal of the Atmospheric Sciences 59, 942 - 958. |
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