ABSTRACT
Most of the weather changes take place in the lower layer of the atmosphere which is known as the troposphere. This layer extends about 11 miles high over the equatorial regions and about 5 miles high over the polar regions. The layer above the troposphere is known as the stratosphere, where there is little water vapour and the lower part appears to be isothermal. There is a rise in temperature towards its upper limit. The boundary between the troposphere and the stratosphere is known as the tropopause. About 20 miles above the Earth the stratosphere gives way to the ozonosphere, where there is a high concentration of ozone which absorbs ultraviolet radiation. The ionosphere starts about 50 miles above the Earth and this is the layer that contains the various radio wave reflecting areas known as the Kennelly-Heaviside (55 miles) and Appleton (150 miles) layers. See Figure 14.
