The atmosphere is divided into five layers - exosphere, thermosphere, mesosphere, stratosphere, troposphere. Each layer has different properties but the most important for weather purposes is the troposphere which contains about 80% of the total atmosphere by weight and on average 2-4% water vapour. The troposphere is the part of the atmosphere closest to the Earth and its depth varies from about 16 km near the equator to about 9 km (5.5 miles) near poles. The temperature in this layer gets colder with height, but the rate at which it falls (the lapse rate) varies considerably. Sometimes, especially at night near to the ground, the temperature actually rises with height - this is called a temperature inversion. Air is in constant motion - the result of inequalities in temperature and pressure between different parts of the troposphere which has a natural tendency to redress the imbalances.

The upper boundary of the troposphere is called the tropopause and immediately above lies the stratosphere. The tops of storm clouds can penetrate a kilometer or so into the stratosphere as they can reach heights of 15 km (9 miles. Belts of strong winds, known as jet streams, often occur in its lowest reaches and just below the tropopause. Some of these winds can reach speeds of up to 320 km/h (200 mph). Long-distance sub-sonic aircraft fly close to the tropopause above any adverse weather, taking advantage where possible of helpful tailwinds. Concorde actually flies in the lower reaches of the stratosphere.