Why do stratospheric conditions differ from tropospheric ones?

Stratospheric conditions differ from tropospheric ones due to variations in temperature, composition, and atmospheric processes.

The stratosphere and the troposphere are two distinct layers of the Earth's atmosphere, each with its unique characteristics. The troposphere is the lowest layer, extending from the Earth's surface to about 8 to 15 kilometres high. This is where weather phenomena occur, and it contains about 75% of the atmosphere's mass. The stratosphere lies above the troposphere, stretching from about 15 to 50 kilometres above the Earth's surface. It's home to the ozone layer, which absorbs and scatters the solar ultraviolet radiation.

One of the primary differences between the two layers is the temperature gradient. In the troposphere, the temperature generally decreases with altitude. This is because the Earth's surface absorbs most of the Sun's energy, which then heats the air above it. Conversely, in the stratosphere, the temperature increases with altitude. This is due to the absorption of solar radiation by the ozone layer, which warms the stratosphere.

The composition of the two layers also varies. The troposphere contains a higher concentration of water vapour, which is virtually absent in the stratosphere. This is because the tropopause, the boundary between the troposphere and the stratosphere, acts as a barrier, preventing the upward movement of water vapour. The stratosphere, on the other hand, contains a higher concentration of ozone.

Atmospheric processes also differ between the two layers. The troposphere is characterised by turbulent air movement, driven by the heating and cooling of the Earth's surface. This results in weather phenomena such as wind, rain, and storms. In contrast, the stratosphere is relatively stable, with little vertical mixing. This stability is due to the temperature inversion, where the temperature increases with altitude, reducing the tendency for convection.

In summary, the stratosphere and the troposphere are distinct atmospheric layers with different temperatures, compositions, and atmospheric processes. These differences are primarily due to the absorption of solar radiation by the ozone layer in the stratosphere and the heating of the Earth's surface, which primarily affects the troposphere.