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Decreases in temperature with altitude

As altitude increases, temperature decreases. Various factors are responsible for this, including air pressure and water-vapour content.


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With every 100 metres, the temperature drops by an average of 0.65°C. Where the air is very dry, such as in an area of high pressure, the air can cool by almost 1°C per 100 metres. This process depends on the air pressure, heat radiation and water-vapour content of the air.

Lower air pressure at altitude

Temperature is usually dependent on air pressure. The higher the pressure, the higher the temperature. Since atmospheric pressure is greatest at sea level, the highest temperatures are generally observed at sea level under comparable weather conditions. The higher one climbs, the further the temperature sinks, due to the decreasing air pressure.

Aside from air pressure, another determining factor in how temperature changes with altitude is the way in which the atmosphere is heated. The atmosphere is mostly warmed by the Earth’s surface. The incoming short-wave solar radiation warms the Earth’s surface, which in turn emits long-wave thermal radiation to the atmosphere above.

Lower water vapour content

The more water vapour the atmosphere contains (see humidity), the more heat radiation it can absorb. When a layer of atmosphere is warmed, it becomes a heat radiator itself, i.e. it re-emits the heat. A large part of the heat from the atmosphere is radiated back to the Earth’s surface. This is called long-wave atmospheric counter-radiation. Counter-radiation also takes place at night. This process with incoming short-wave radiation and long-wave atmospheric counter-radiation constitutes the natural greenhouse effect.

The water vapour content of the atmosphere depends on the air pressure, and decreases as altitude increases and pressure decreases. So, as altitude increases, the ability of the atmosphere to absorb thermal radiation and radiate it back to the Earth’s surface lessens. Consequently, with increasing altitude, the atmosphere becomes more permeable to heat radiated from the Earth’s surface. The heat that is not absorbed leaves the atmosphere and dissipates in space.

Rising warm air cools down

When warm air rises, it expands with altitude due to the decrease in pressure. The expansion of the air requires energy, which is drawn from the heat that the air is carrying with it. This means that as it expands with increasing altitude, rising air becomes cooler and cooler.