The representation of the climate of a region by the frequency and characteristics of the air masses under which it lies; basically, a type of synoptic climatology. It is a development of the representation of the weather associated with winds of different directions (thermal wind roses, etc. ) by taking account of the source and trajectory of the air, and it gives a more dynamic picture of the climate than do monthly averages. The first detailed study was by E. Dinies (1932). Dinies gave tables of average temperature, humidity, and cloudiness in Germany associated with eight classes of air in winter and summer (Durst 1951). Similar tables have since been constructed for many parts of the world.