2012 年 32 巻 3 号 p. 149-156
An urban cool island is a meteorological phenomenon in which the air temperature in a park or green space is lesser than that in the surrounding built-up area. Few studies have investigated the relation between tree height, landform characteristics, and temperature. In this study, 2-m-resolution brightness temperatures were measured in Shinjuku-gyoen National Garden (ca. 58ha) and around area, central Tokyo and in Naganuma Park (ca. 36ha) and around area in a suburb of Tokyo, Japan, on calm summer nights in 2005 and 2006, respectively, using an airborne thermal sensor. Tree heights were measured using an airborne LiDAR (light detection and ranging) sensor. In this garden, areas with greater tree heights were found to have higher brightness temperatures. In Naganuma Park, where a broadleaf deciduous forest extends in a hilly area, the highest temperature was observed for the southwest-facing slope; this indicates that the southwest-facing slope receives direct sunlight in the afternoon for a longer time than other sides of the slope; this leads to a difference in heat accumulation among the slope sides, in turn affecting the nighttime brightness temperature and thus maintaining thermal inertia. Furthermore, in this park, the temperature in concave landforms was lower than that in convex landforms, indicating that the air cooled by nocturnal radiation was trapped in concave landforms (cool air lake phenomenon).