Effect of Mountain Breeze on Urban Heat Island

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In Germany, for the purpose of mitigation of heat stress in summer and air pollutant load in winter, urban planning with consideration on the urban climate protection represented by "Luftleitbahnen" (Urban ventilation lanes) is practiced effectively. We Japanese have to analyze basic wind data statistically for the discussion on the necessity of urban ventilation lanes in Japanese cities, e.g. frequency of calm days in each season, histogram of wind velocity. In this study, the investigators reviewed on studies and practices on urban ventilation lanes and discussed on the probability to apply "Luftleitbahnen" to Japanese and Asian cities. Nocturnal mountain breeze appears in Nagano City of Japan, a typical basin秒ottom city like Stuttgart in Germany, and it invades to central part of the urbanized area. In meteorological conditions which mountain breeze appears, urban heat island would also appear and thermal mitigation of urban heat island by mountain breeze as a relative cooler air flow is expected. In this study, features of the mountain breeze in Nagano was clarified by meteorological observations and its thermal mitigation probability on urban heat island, namely, an availability as urban ventilation lanes was discussed. Based on field observations and numerical simulation of cold air drainage flows, the investigators proposed a KLIMAATLAS of Nagano considering mountain breeze along the Susobana River.