关键词: 热岛强度, 平面结构, 北京城市, 建成区, 等温线图, 风速, 天气状况, 热岛形成, 天气条件, 1981年

Abstract: It is generally accepted that urban heat-islands will constantly change their formas well as their intensity as the result o’f change in the background weather conditions. Although variations in heat-island intensity have been well documented, studies concer-ning veriations in heat-island form are few. This is mainly due to the fact that most of the heat-island studies in the, past were illustrated with only one detailed isotherm map based on one temperature survey, usually at times when heat-islands are strongest, to depict the spatial structure of the heat-island concerned.In this paper, the spatial structure of the heat-island in Beijing has been investiga-ted through more than 60 temperature surveys conducted in January, April, July and October, 1981. Temperature data for 14:00 and 21:00 or 22:00, 23:00 were obtained by both stationary observations and mobile traverse observations on pre-determined sites within and around the built-up areas. Data from a few meteorological stations in the suburbs were also used. Eesults show that the spatial structure of the heat-island in Beijing varies greatly at different times and the patterns of isotherms of the heat islands observed were all different from one another. However, it is found out that the varia-tions of the spatial structure of heat island are closely related to the intensity of heat island, and a few broad types of heat island spatial structure patterns can be recogni-zed:1. Calm-light air clear night type: As shown in Fig. 2, the pattern of isotherms roughly coincides with the urban morphology with highest temperature in the heart of the old city. Although the concentric pattern of the isotherms can’ ibe detected, there are some outstanding peaks on the ’fringe of the heat island. This type takes place in the calm-light air clear night, especially in winter when heat island reaches its maximum intensity.2. Light ibreeze clear sky type: As shown in Fig. 3, the pattern of isotherms is quite different from that in’ Fig. 2. The intensity of the heat island decreases due to light wind (about 2-3 ms"1) and some of the outliers of the built-up areas are excluded from the heat island. The breaking up of the heat island peak in the old city into two is a remarkable feature of this type.3. Gentle-moderate breeze clear sky type: As shown in Fig. 4, the pattern o’f isotherms is drastically different from those in Fig. 2 and Fig. 3. Whenever wind speed reaches 3ms""1 or even higher, the urban temperature is only slighly higher than the rural temperature, and within the urban heat island there are many small peaks near the anthropogenic heat sources.4. Cloudy type: Whenever the sky is overcast, the heat island is very weak. The pattern of the isotherms, as shown in Fig. 5 is different from that in Fig. 4, which is also a pattern of weak heat island but d.ue to windy weather. The outstanding feature of this type is the lack of correspondence between the pattern of isotherms and the urban morphology.