Weather is the condition of the atmosphere at a particular place over a short period of time. Climate is the average weather conditions of a place over a long period of time, of at least over 30 years.

Atmosphere

Atmosphere is the layer of air surrounding Earth, held on by the pull of Earth’s gravity. As the pull of gravity decreases with an increase of vertical distance, most of the Earth’s atmosphere is concentrated near the Earth’s surface.

The atmosphere is made up of dust particles, water and gases. Three important gases in the atmosphere are ozone, water vapour and carbon dioxide.

The ozone layer absorbs harmful ultraviolet radiation and shield people against its effects. Water vapour helps to regulate the amount of heat Earth receives. It prevents overheating by reflecting, scattering and absorbing solar radiation and prevents excessive cooling through absorption of terrestrial radiation.

The atmosphere is divided into four layers, as described below:

1. Troposphere: the layer nearest to Earth’s surface, extending an average of 10 km vertically above the Earth’s surface.

This layer experiences weather changes as most of the atmosphere’s mass, water vapour and dust particles are found there. In this layer, temperature drops as height increases with an average rate of 6.4° C per 1000 m.

2. Stratosphere: the layer above troposphere, where temperature increases with height due to the abundance of ozone, which absorbs ultraviolet radiation from the sun.

3. Mesosphere: The next layer above stratosphere, where temperature decreases with height and it extends from about 50 km to 80 km above sea level.

4. Thermosphere: the fourth layer of the atmosphere, where temperature increases quickly with height and it is of a distance of 80 km to 480 km from the Earth’s surface.

The top three layers do not experience changes in weather as they contain little atmospheric materials.

Solar Radiation (Insolation)

All living things on Earth depend on the sun for energy. Solar energy travels to Earth via space in the form of solar radiation.

But, Earth absorbs only about 45% of this incoming solar radiation as the some of the energy is scattered and reflected back into space and the rest is absorbed by the atmosphere.

The solar radiation that reaches the Earth’s surface is converted into heat energy.

Terrestrial Radiation

The warm ground then radiates the energy back into space in the form of terrestrial radiation, and water vapour and carbon dioxide in the atmosphere absorbs part of it as it passes through the atmosphere.

Insolation and terrestrial radiation provide the energy to keep the atmosphere in constant motion, thus causing varying weather conditions. These weather conditions can be described by the major elements of weather.

These major elements are temperature, precipitation, humidity, winds, pressure and clouds.