Atmospheric Boundary Layer Studies

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The, usually turbulent, atmospheric boundary layer (ABL) with a typical depth of about 1 km, is where most of us live, work and play. My research group have worked on many issues related to ABL flows in the past, including the flow over complex terrain (hills and roughness changes for example) using both models and field studies. Despite a long record of ABL studies by many research groups there are still opportunities for significant improvements in our understanding and forecasting of some important practical issues, such as fog and land surface conditions.One objective over the next 5 years will be to study fog within the boundary layer and to carefully explore the conditions under which it can develop and later dissipate. These involve a mix of turbulent transfer of heat, water (vapor and droplets), radiation (long and short wave) and cloud physics processes.Another important applied ABL research area is a study of winter road conditions. In addition to turbulent transfers, plus surface and sub-surface conditions these can depend to a considerable extent on solar and long wave radiation fluxes, strongly influenced by the presence of low level cloud. Coupling with an improved ABL model would, for example, allow an extension of the very widely used METRo forecast model, developed 17 years ago at Environment Canada.Our main approach will continue to be turbulent boundary-layer modeling. There are two computer-based approaches, Large Eddy Simulation (LES) and solving the Reynolds Averaged Navier-Stokes (RANS) equations with some form of turbulence closure. My research group has used both in the past for different projects. We will focus here on RANS modeling, but there are situations where LES has advantages, for example to investigate fog "patchiness", and vehicle wake situations.I also plan to explore a detailed closure issue in RANS models. In general RANS models will include turbulence kinetic energy (TKE) as one of the variables and either a "master length scale", l, or a TKE dissipation rate, , as another. These appear satisfactory in most cases and rely to some extent on the concept that energy is put into the turbulence spectrum at large scales and then "cascades" through the spectrum to be dissipated and converted to heat at very small scales (< 1mm). In some cases such as wind turbine wakes, or wakes behind vehicles, there is an additional input of TKE at an intermediate scale (blade or vehicle width). We will investigate ways to effectively represent this process.The main research goal will be to expand the range of ABL studies that my group have an expertise in and to include radiative effects. These include applications, such as fog, with significant impacts on road and air safety. We will be interested in exploiting these potentials through industry or government collaboration but rely on NSERC Discovery grant support for the fundamental research needed to initiate and support the more applied studies.