This chapter examines the controls on mountain weather and climate from the standpoint of the geographical determinants of the meteorological elements – radiation, temperature, air pressure, vapor pressure and wind. The geographical factors that most strongly influence these elements and hence mountain climates are latitude, continentality, altitude, and the topography.

LATITUDE

The influence of latitude on the climate of different mountain systems shows up in a variety of ways. First, solar and net radiation and temperature broadly decrease with increasing latitude and, as a result, the elevations of the tree line and of the snow line decrease polewards. This means that the belt of alpine vegetation (above tree line) and the nival belt of permanent snow and ice are represented on much lower mountains in high latitudes than in the tropics (see Figure 1.1, p. 3). Second, the latitude factor is apparent in the relative importance of seasonal and diurnal climatic rhythms. This is determined by the seasonal trend in the daily Sun path at different latitudes (Figure 2.1). Seasonal changes of solar radiation, day length and temperature are basically small in low latitudes, whereas the diurnal amplitude of temperature, for example, is relatively large. Thus, Hedberg (1964) characterizes the equatorial mountains of East Africa as experiencing “summer every day and winter every night.”