Comprehensive Outdoor Scale Model Experiment
for Urban Climate
(COSMO)


1/5 larger scale model
The 1/5 scale model is the main part of this project. The 1/5-scale model surface geometry consists of cubic concrete blocks 1.5-m on a side with 0.1-m thick walls. Inside blocks are vacant. The blocks are distributed in an array on concrete pavement that has a total area of 100 x 50 m2 (Figure 1). The area density and alignment of the concrete blocks are variable. The cubes are currently aligned in a square array with plane area density 0.25 (Figure 2).  X, Y and Z are defined as the longer and shorter axes parallel to the streets, and the height from the concrete basement, respectively. The concrete pavement is flat with 1/200 inclination along Y axis to drain rainfall.  The same concrete material was used for cubic block and basement.

Figure 1 Plane view of the scale model site. (1), (2) and (3) indicate the locations of tower of the north, center, and south, respectively.


Figure 2 1/5 larger scale model

For the water balance, a drainage system surrounding the concrete basement has an orifice at the exit that will allow us to estimate the water loss (rainfall / runoff) independent of the turbulent moisture flux.

Three towers were constructed at X = 8 m, 50 m and 92 m along the central X-axis (Y = 0). Air temperatures were measured at several heights of three towers using unshielded, 50-m-thick bare thermocouples. We judged from the observed vertical temperature profiles that the depth of IBL ranged from Z/H = 2.5 to 4.0 at the distance of central tower, where H is the cube height. Considering the minimum IBL height, a compact sonic anemometer with 0.05 m sensor-span and 50 Hz sampling frequency (Kaijo TR90-AH), and an infrared CO2/H2O open-path analyzer (LI-COR LI-7500) were installed at a height of 3 m (Z/H = 2) of the central tower. They were used for the estimation of sensible and latent heat fluxes through the eddy covariance (EC) method. Upward and downward shortwave and longwave radiation were measured separately using a radiation-balance meter (Eiko MR-40) 4.5 m above the ground (Z/H = 3).

The energy balance residual of the net radiation minus the turbulent fluxes cannot be used instead of the conductive flux measurements due to the energy imbalance problem with the EC method (Kanda et al., 2004). This is a serious problem in real cities since the direct measurement of heat storage is quite difficult. To precisely close the energy balance, the conductive heat fluxes of all facets in a unit area should be measured. As a great advantage of scale models, this is possible using very thin and highly-accurate heat plates (Captec HF-300 with 0.3 m x 0.3 m size and 0.4-mm thickness) and carefully coating them with the same material that the obstacles are made of.  A total of 200 heat plates completely cover a unit of constituent surfaces including four vertical walls, roof, and floor (Figure 3).  The heat sensor can also measure the surface temperature as well as the heat flux.


Figure 3 Cluster of heat plates on one model unit

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