Field observations on thermal effects of green space in an urban area.

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In order to clarify the thermal effect of green space in an urban area, two kinds of field observations were performed. One is concentrative measurement about micro-climate in and around a green space in summer. To get a horizontal air temperature distributions, the measured line was set along the sea-breeze direction from the bare ground to the tree stand. The heat balance and the correlation of instantaneous fluctuations of air temperature and wind were also measured with the ultra sonic anemometer both in the bare ground and under the forest canopy. The peripheral part of forest, which is adjacent to the asphalt pavement road, was strongly affected by surrounding built-up area regardless of the wind direction.Second observation is air temperature measurements at ten points in and around Hiroshima City during one year. These were measured at the height of 4m above ground with Platinum resistance thermometer set in the ventilated double rectangular colum shelter in every 1 minute. In summer, air temperature under the forest is lower than surrounding area about 2ﾟC as a daytime 5-hours average. But it disappears with leaf fall. On the other hand, temperature difference during nighttime is constant through the year. It means that the daytime temperature difference is due to sunshade effect and transpiration but that of nighttime results from artificial exhaust heat in surrounding area.