Review of Japanese Urban Models and a Scale Model Experiment - Meteorological and Air Quality Models for Urban Areas - page 34

5.2.2 Comprehensive Outdoor Scale
Model - COSMO - Experiments for Urban Climate

In September 2004, the Japanese Urban Climate Group of the Core Research for
Evolutional Science and Technology (CREST) started the Comprehensive Out-
door Scale Model experiments for urban climate (hereafter, COSMO) at scales of
1/5 and 1/50 of real world. The purpose of COSMO is to obtain a comprehensive
dataset including (1) energy balance, (2) land surface parameters, and (3) turbu-
lent structures. The 1/5 model surface geometry consisted of concrete cubes 1.5-m
on a side with 0.1-m thick walls. The blocks were distributed in an array on con-
crete pavement that has a total area of 100 50 m 2 . The smaller 1/50 scale model

was used to investigate the scale effect, which had the same surface geometry and
material as the larger model. The models are located next to each other. In addition
to the conventional turbulent flux estimate using the eddy covariance method, the
direct measurement of the heat storage using thin heat plates allowed us to precisely
estimate the surface energy balance closure. It is equipped with 60 thermocouples
and 15 compact sonic anemometers aligned in lateral direction at 2H (H is the cube
height) to detect the multiple scales of turbulent organized structures.
The roughness length for heat is a very important surface parameter but there
are little empirical data. COSMO data were used successfully to develop a theo-
retical relation between the logarithmic ratio of roughness length for momentum to
heat (

×

B -1 ) and the roughness Reynolds number (Re ∗ ). Values of B -1 associated

κ κ

Fig. 5.2 κ B -1 versus Re ∗ (from Kanda et al., 2007). Open circles : large-scale model (L); open
squares : small-scale model (S). Open triangles (VG: light industrial area, Vancouver), crosses
(SU: business district, Tokyo), and filled circles (MK: dense residential area, Tokyo) correspond
to urban data. Lines are from the theoretical relationship. The dotted line is from Brutsaert (1982).
The solid line is from scale model data