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Project properties |
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| Title | Does the variation of the surface temperature have an effect on dust-devils and other coherent structures in the convective boundary layer? |
| Group | Meteorology and Air Quality Group |
| Project type | thesis |
| Credits | 36 |
| Supervisor(s) | Arnold Moene and Oscar Hartogensis |
| Examiner(s) | Prof. dr. AAM Holtslag |
| Contact info | Arnold.Moene@wur.nl |
| Begin date | 2018/01/01 |
| End date | 2019/02/01 |
| Description | Under strongly unstable conditions violent but interesting flow structures develop in the atmospheric surface layer: dust-devils, micro-fronts and other coherent structures. A field study in which the Meteorology and Air Quality Group participated (MATADOR 2002, Renno et al., 2004) revealed that the surface temperature of the bare soil showed large dynamics on turbulent time scales (order of minutes). Whereas these dynamics seem to be induced by the turbulence, it is not clear to what extent it influences the turbulence (and possibly the dust devils) in return.
Fiedler and Kanak (2001) used a Direct Numerical Simulation (DNS) to study the occurrence of dustdevil-like structures in a Rayleigh –Benard flow. They were able to identify the location of the formation of these vortices. The vortices appeared to develop at the location ware different thermals meet. Whereas Fiedler and Kanak used prescribed surface fluxes, Hunt et al. (2003) made a study of the effect of thermal diffusivity in the soil on the characteristics of the motion in the convective boundary layer using DNS (not focussing on dust-devils in particular). The objective of this research project is to link our experimental results with the dynamics predicted by a direct numerical simulation. The main question to be answered is: does the interaction between turbulence and soil temperature impact on the turbulent field and more specifically on the formation and development of coherent structures (like dust-devils). Sub-questions are: • are we able to reproduce the results of Fiedler and Kanak (2001)? • how are turbulence and surface temperature coupled? • does the interaction of turbulence with the surface temperature impact on the development of dust devils? The work involved in this project consists –among others– of the following tasks: • analysis of the MATADOR 2002 surface temperature data to characterize the dynamics of the surface temperature; relate those dynamics to observed turbulence. • 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. • run and analyse simulations for a configuration similar to that of Fiedler and Kanak (2001) (with prescribed surface flux); analysis includes the development of algorithms to identify dust-devillike vortices. • run and analyse a simulation similar to the previous, but now with the interactive surface temperature boundary condition to study the difference in terms of development of turbulent structures References Fiedler, B.H. and K.M. Kanak, 2001. Rayleigh-Bénard convection as a tool for studying dust devils. Atmospheric Science Letters 10.1006/asle.2001.0043. Hunt, J.C.R., A.J. Vrieling, F.T.M. Nieuwstadt and H.J.S. Fernando, 2003. The influence of the thermal diffusivity of the lower boundary on eddy motion in convection. J. Fluid Mech. 491, 183-205. Renno, Nilton O., Vincent J. Abreu, Jacquelin Koch, Peter H. Smith,, Oscar K. Hartogensis, Henk A. R. De Bruin, Dirk Burose, Gregory T. Delory, William M. Farrell, Christopher J. Watts, Jaime Garatuza, Michael Parker, and Allan Carswell, 2004. MATADOR 2002: A pilot field experiment on convective plumes and dust devils. Journal Of Geophysical Research, 109, E07001 |
| Used skills | A combination of data analysis and Direct Numerical Simulation |
| Requirements | |