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

为了弄清城市绿地的热效应，进行了两种实地观测。一种是集中测量夏季绿地及其周围的小气候。为了得到水平的气温分布，沿海风方向设置了从裸露地面到林木林的测线。用超声波风速仪测量了裸露地面和林冠下的热平衡和气温、风的瞬时波动关系。与沥青路面相邻的森林外围部分，无论风向如何，都受到周围建成区的强烈影响。第二个观测是一年中广岛市及其周围10个点的气温测量。在离地面4m的高空，每隔1分钟用铂电阻温度计在通风的双矩形柱罩内测量一次。夏季，森林下的气温比周围地区低约2ﾟ℃，白天平均5小时。但随着树叶的落下，它就消失了。另一方面，夜间的温差在一年中是恒定的。这意味着白天的温差是由遮阳效应和蒸腾作用造成的，而夜间的温差是由周围地区的人工排气热造成的。

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.