HEAT ISLAND STRUCTURES IN THE NIGHTTIME OF SUMMER SEASON IN FUKUOKA METROPOLITAN AREA

The data obtained in the summer seasons of 2003 and 2004 were analyzed to examine the formation process of the urban heat island. The heat island structures with concentric isothermal lines are formed over Fukuoka metropolitan area when the background wind is weak. When the wind is strong, they are deformed because of the advection and the mixing of heat. When the background wind is weak and the cloud amount in the nighttime is small, the radiation cooling occurs and the falling rate of temperature in the rural area becomes larger than that in the downtown area. Its difference forms an obvious heat island structure over the whole area of Fukuoka metropolitan area. The heat island intensities decrease with the increase of the background wind speed and the cloud amount. The larger the solar radiation is in the daytime, the stronger the heat island intensities become in the nighttime, because the heat stored in the down town area is released in the nighttime.