Chapter 1 Introduction
6.2 Perspectives
able improvement to the wind speed of the meso-scale meteorological model when using a low resolution. This was expected with the use CIM, as the calculation of the surface fluxes in low resolution meso-scale models have been enhanced. Ad- ditionally it was seen that CIM did not have an impact on the computational time.
These results provided a solid foundation for the future coupling of meso-scale and micro-scale models. The use of CIM has insignificant impact on the com- putational time and can hence be used in low resolution models to provide high resolution vertical profiles.
6.2 Perspectives
Further work is needed to address some of the issues that have been encountered during our studies. Firstly, when comparing CIM with the C.F.D experiment from Santiago et al.[2007] andMartilli and Santiago[2007], it was seen that even though the horizontal wind speed was in very good agreement, there were still some dif- ferences between the T.K.E profiles. CIM seems to underestimate the T.K.E but this does not appear to have an influence on the diffusion process. One of the questions which rises is the importance of the magnitude of the T.K.E particularly in the transition zone above the obstacles and the canopy.
Secondly, when the buoyancy term is added to the T.K.E equation, we observed that to obtain results in agreement with the well-known and accepted theories, a coefficient has to be added. The fact that this coefficient is a function of the φm
function from Businger et al.[1971] means that this equation cannot be used in all cases. A simple diffusion process using a 1.5 order turbulence closure was adopted for CIM. The use of the φm functions in the resolution of the T.K.E equation is not intended to be a permanent solution. These functions can only be applied over a plane surface when it can be assumed that the fluxes are constant. In the case where obstacles are constant this statement does not hold true and hence we expect the φm functions to be erroneous. In order to generalize the use of CIM and the formulations as proposed by Mauree et al. [2014b,a], it is necessary to find a new formulation for this coefficient and to understand why this correction
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is needed.
Thirdly, one of the major obstacles that we came across during this study is the lack of experimental data to validate the simulations that have been made. The aim of CIM was to provide highly resolved meteorological data at the neighbor- hood scale. In neutral conditions results were validated with a C.F.D experiment.
However in other stability conditions and in real cases, no appropriate dataset could be exploited. Various means were hence designed to justify the method- ology that was chosen and to validate the results which were obtained from the experiments that were conducted.
The integration of CIM in WRF was only a preliminary step to test the valid- ity of CIM when coupled with a meso-scale model and an urban parameterization scheme. A few questions are still to be investigated for that purpose. For the simulations that were run it was noted that BEP had higher walls and surface temperatures (up to 10K more than the air temperature). Although this might be the case during summer, it is hardly plausible that such a situation will occur when the sun is very low in winter at high latitudes. Further investigations are therefore needed to understand why the wall temperatures are so high.
Coupling CIM and WRF with another micro-scale model may bring an insight to this particular question. The coupling with another model should prove to be relatively simple. CIM can provide vertical meteorological profiles to this model and needs in return only fluxes and obstacles characteristics.
For the purpose of this study, a theoretical domain was designed and used.
Although this was enough for the present context, this type of domain is not the best configuration for using meso-scale meteorological models. It is therefore strongly advised, in the future, to use CIM on a more realistic and smaller domain over a longer time period and where data is available to validate the meteorolog- ical profiles as well as the energy use. In such a configuration, it would then be judicious to analyze the influence of land use changes on urban energy consump- tion. Urban planning scenarios have to be evaluated to determine whether the
6.2 Perspectives thermal comfort of the inhabitants as well as legislation concerning the energy use in buildings are respected in the construction of new neighborhoods in urban areas.
In view of the results obtained from the current study, CIM can be used as a tool to couple meso-scale meteorological models to micro-scale models. It can thus be fully integrated in a meso-scale model like it has been done with WRF and precise vertical meteorological profiles can be provided to building energy models.
This will prove to be very useful in the design of more energy efficient buildings as well as in evaluating urban planning scenarios.
Furthermore, since CIM has been built to be a standalone column model, it can be used in various type of model to improve the representation of the surface in low resolution meteorological models, and at the same time decrease computational time. It can thus prove very useful in global climate model where it is very costly to use high vertical resolution.
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