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

为了明确城市绿地的热效应，进行了两种类型的野外观测。一是夏季绿地内部及周边小气候的集中测量。为了得到水平的空气温度分布，测量线沿海风方向设置，从裸露的地面到树桩。利用超声波风速仪测量了裸地和林冠下的热平衡以及气温与风的瞬时波动的相关性。森林外围部分与沥青路面道路相邻，无论风向如何，都受到周围建成区的强烈影响。第二项观测是一年内在广岛市内及周边10个地点的气温测量。在距地面4米的高度，每隔1分钟在通风的双矩形柱遮蔽处用铂电阻温度计测量一次。在夏季，森林下的气温比周围地区低约2ºC，白天5小时的平均值。但它会随着落叶而消失。另一方面，夜间的温差全年不变。这意味着白天的温差是由于遮阳作用和蒸腾作用造成的，而夜间的温差是由于周围地区的人工排热造成的。

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.