In the course of the year, the rain belt caused by the intra- tropical convergence (ITC) shifts following the zenith of the sun between the two tropics, within which there are two rainy seasons per year near the equator. With increasing distance from the equator, the time interval between these two rainy seasons decreases, because the first takes place on the way to the zenith and the ITC to the tropic and the second on the way back. In the wet savannah there are still two clearly separated rainy seasons. In the dry savannah they are connected in a rainy season. In the thorn savannah they merge into a relatively short rainy season. In the vicinity of the tropics , the melded rainy season is so short and brings so little rainfall that there are tropical deserts here . The tropical deserts within the tropics lie under the descending hot, drying air masses of the Passatin version for most of the year and therefore cannot contribute anything to evaporation or the development of the ITC under the zenith of the sun . The subtropical deserts beyond the tropics are even permanently below the subtropical high pressure belt . Both deserts inside and outside the tropics are known as tropic deserts , in which only very short or no rainy seasons take place.
The areas in the temperate zone beyond the 42nd parallel come under the influence of the westerly wind zone in the winter months . Here you can find the winter rainy climate of the west sides . This winter rain no longer falls under the concept of rainy seasons in the narrower sense, although the summer months are arid and in summer only heat thunderstorms bring some precipitation. Factors such as the wind relationships, the origin of the wind from sea or land, the height above sea level and the vegetation influence rainfall advent here stronger than the seasonal sunlight. Where forested mountains favor precipitation in the form of incline rain , it will rain more at altitude than in valleys or in the rain shadow of mountains.