Abstract
Cool island (lowtemperature area) phenomena in urban green spaces were analyzed based on longterm continuous temperature observations. Cool island intensity (CII), which is defined as the temperature difference between the green space and its surrounding built-up areas, shows diurnal variations. In a grass area, CII is weak in the daytime and strong at night. On the other hand, CII is strong for both day and night in forest areas. The reason for this is that radiative cooling from the surface of grass and forest at night might be more effective in the green space than in the periferal built-up. It is also pointed out that CII shows little variability in either fine or cloudy weather.
Surface air temperature observations along a horizontal straight line in and around the green space reveal cooling in the peripheral built-up area caused by the advection of cooled air in a green space. Vertical temperature profiles in the green space show ground inversion which reaches 60 meters in height during the night. No clear ground inversion can be found in urban built-up areas. Based on these results, the nocturnal heat island in an urban area is expected to be reduced by the cool island effect in urban green spaces.
