Utilization of passive cooling effects by land and sea breeze circulation is considered to be very effective for reducing summertime air temperature in urban areas, because most of the major cities in Japan have developed in the costal area. Before the advance of the super computers, it had been difficult to simulate the airflow field of urban areas, with taking into account various scales of urban structures, such as buildings, streets and rivers. In this study, the Earth Simulator was used for the urban environmental analysis for the first time. We developed a new thermal environmental analysis system, which can deal with the atmospheric environment from individual building scale to urban scale. Using this code by incorporating the Coriolis force and potential temperature, we simulated the thermal environment in the ten-kilometers square area of central Tokyo with 5m grid spacing. As a result, regions with lower wind speed and higher air temperature were found aound high-rise buildings. It was also confirmed from the computed and observation results that airflow exists along the Nihonbashi-river and Megro-river. As for the air temperature, temperature distribution near the ground obtained from the computational results matched fairly well with that of observation, and the RMS error between observation and numerical results of 173 points was 1.1℃.
