The atmosphere is divided up into a number of layers as follows:

1. The Troposphere. This layer stretches from the surface of the earth up to 18 kilometers above the earth. Most of the weather changes occur in this layer.
2. Stratosphere. This layer stretches from 18 to 32 kilometers above the earth. Very little water vapour is found in this layer.
3. Ozonosphere. This layer lies between 32 and 80 kilometers above the earth. A high concentration of ozone is found in this layer which absorbs ultra violet radiation from the sun. Ozone is an unstable form of oxygen formed by electrical discharges.
4. Ionosphere. This layer lies between 80 and 300 kilometers above the earth. It contains gas particles which have been ionised by the sun’s radiation. This layer is responsible for the reflection/refraction of radio waves. Ionised particles are particles that have either had an electron removed or added to its mass.

Heating of the atmosphere.

Since most of the weather changes occur in the troposphere, temperature changes in this layer are most important. The sun is the principle source of light and heat for the earth. Heat travels in the form of short wave radiation (ultra violet) which passes through the atmosphere without noticeably warming it. When it reaches the earth’s surface some of the heat is absorbed by the surface. The heat received by the earth from the sun is known as “insolation”. The amount of “insolation” per unit area varies with the latitude. The higher the latitude, the less this amount. The increase in temperature is dependent on the amount of “insolation” and the specific heat of the earth.

The specific heat of a substance is defined as the amount of heat required to raise the temperature of a specified quantity of the substance by 1° (C). If we assume a constant “insolation”, a surface with a high specific heat warms and cools less quickly than a surface with a low specific heat. The sea temperature in non-tidal waters changes very little over a period of 24 hours. As a general rule, sea temperatures are less than the temperatures of adjacent land by day and greater at night. In addition to receiving heat, the earth, being a warm body, also radiates heat and when the amount of radiation exceeds the ”insolation”, it cools, ie at night. The heat transferred to the atmosphere has a very profound effect on the weather.

How is it transferred?

1. By radiation. Whilst the earth’s surface is heated by the short wave (UV) radiation of the sun, it in turn, radiates heat in long wave form (infra red). This warms the lower layers of the air. On a cloudless night, most of the heat is radiated into outer space. When there is cloud cover, most of the heat will be reflected back to earth. The clouds act as a sort of blanket.
2. Conduction. Air in contact with the earth is warmed during the day and cooled at night.
3. Convection. Air which is warmed expands and its density decreases. Since this makes it lighter than the cooler air around it, the warm air rises. Convection takes large amounts of warm air and water vapour from the surface to the upper levels. When the water vapour condenses into water droplets and precipitation occurs, the latent heat remains. Most of the atmospheric heating takes place this way.
4. Turbulence. Air which flows over a rough surface tends to be reflected upwards, ie the mountains and hills will deflect the heat upwards. The rising air will be replaced by air from levels up to 600 metres. The rising air carries it’s warmth with it and the falling air brings its coolness.