The climatic snow line is the boundary between a snow-covered and snow-free surface. The actual snow line may adjust seasonally, and be either significantly higher in elevation, or lower. The permanent snow line is the level above which snow will lie all year. Background Snow line is an umbrella term for different interpretations of the boundary between snow-covered surface and snow-free surface. The definitions of the snow line may have different temporal and spatial focus. In many regions the changing snow line reflect seasonal dynamics. The final height of the snow line in a mountain environment at the end of the melting season is subject to climatic variability, and therefore may be different from year to year. The snow line is measured using automatic cameras, aerial photographs, or satellite images. Because the snow line can be established without on-the-ground measurements, it can be measured in remote and difficult to access areas. Therefore, the snow line has become an important variable in hydrological models. The average elevation of a transient snow line is called the "climatic snow line" and is used as a parameter to classify regions according to climatic conditions. The boundary between the accumulation zone and the ablation zone on glaciers is called the "annual snow line". The glacier region below this snow line was subject to melting in the previous season. The term "orographic snow line" is used to describe the snow boundary on surfaces other than glaciers. The term "regional snow line" is used to describe large areas. The "permanent snow line" is the level above which snow will lie all year. Snow lines of global regions The interplay of elevation and latitude affects the precise placement of the snow line at a particular location. At or near the equator, it is typically situated at approximately above sea level. As one moves towards the Tropic of Cancer and Tropic of Capricorn, the parameter at first increases: in the Himalayas the permanent snow line can be as high as , whilst on the Tropic of Capricorn, no permanent snow exists at all in the Andes, because of the extreme aridity. Beyond the Tropics, the snow line becomes progressively lower as the latitude increases, to just below in the Alps and falling all the way to sea level itself at the ice caps near the poles. In addition, the relative location to the nearest coastline can influence the elevation