RECOMMENDATIONS FOR PLANNING
6.2 Securing the Local Air Exchange

Surfaces with strong nightly cooling (dependent upon the type of soil, plant growth, and extent of built uses) or with large "relief energy" (dependent upon slope inclination, slope form, and surface layout) contribute to the production of local thermally-induced wind systems. In connection with the local air exchange, the topographical conditions do not merely exert a passive effect on wind flow through braking, diversion, or canalization. Much more so, under low-wind weather conditions they take a substantially more active role. Therefore it is proper to speak of "climatic surfaces" in view of their associated balancing effects on climate and ecology.

The term "climatically active surfaces" refers to both the thermal and the topographical requirements of the local air exchange and thus refers to the entire system of cold air production areas and fresh air corridors. The resultant air exchange processes are based on the typically nightly temperature differentials between neighboring areas. According to the spatial size, these are termed as "cold air flows", "slope winds", or "mountain winds." "Corridor winds" are also referred to where they occur at the edge of large cities (KUTTLER, 1993) (cf. Chapter 4.3.2).