COSMO -Introduction

Comprehensive Outdoor Scale Model Experiment
for Urban Climate
(COSMO)

Introduction

For understanding the unique features of urban climates, there have been many studies in real cities in which data was acquired using towers, aircraft, and satellites. However, such full-scale studies have not yet provided a comprehensive understanding of the complicated physical processes that contribute to urban climate. As a complementary method, we have also done studies using a reduced-scale model. Such a model has the advantages of allowing us to make complete measurements and to obtain data on a relatively uniform area. For example, we can probe the physical processes within and above the roughness sub-layer more completely than those in a real urban area. Also, by working with a uniform area, the results are easier to interpret and more suitable for urban modeling than data from real cities. Outdoor experimental studies using relatively large scale obstacles (h~1 m) such as MUST (Yee and Biltoft, 2003) and Kit FOX (Hanna and Chang, 2001) focused on dispersion processes and did not analyze the energy balance. Thus, we are continuing to improve upon our studies with reduced-scale models by increasing the scale, including detailed analysis of the energy balance.

In September 2004, the Japanese Urban Climate Group of CREST (Core Research for Evolutional Science and Technology) has started outdoor model experiments at a scale of 1/5. Our group has been running a 1/50-scale experiment since 2002 (Kanda et al., 2005a), but the scale is too small to investigate the microclimate within and above the canyon; also, the mismatch of the thermal volumetric heat capacity with real cities is too large in the 1/50-scale model. Use of the 1/5 scale model should allow us to overcome these problems and we expect to obtain a clearer understanding of scaling by comparing results from both models.