Study of the thermal structure of a town in a narrow valley

Abstract

This study examines the influence of urban and topoclimatic factors on the temperature field of Stolberg, Germany, a densely built up town in a valley, on the basis of stationary and mobile measurements during cloudless and nearly calm weather conditions. Qualitative and quantitative statements are made about the extent of influence by invariable parameters (percentage of sealed area, height) and by variable conditions (wind velocity, time, temperature amplitude) on thermal conditions in the investigated area. An observed influence of cold air on the temperature field near the ground required further study of wind field influences due to topographic conditions and of an analysis of intensity and frequency of valley inversions. Regarding clear and calm weather conditions, results show a significant relationship between thermal conditions and the percentage of sealed area, as well as topographical height. As a result of roughness of the built up area, the nocturnal urban excess temperature is not reduced by cold air drainage until the second half of the night. The high production of cold air causes the nocturnal component of a mountain and valley wind regime:, which explains the accelerated cold air transport from above the urban canopy layer as well as the frequency of valley inversions. While ground level inversions exist in the rural area of the valley, the urban heat island effect causes an inversion at a higher level above the developed valley area.