The Atmosphere

Meteorology is the study of the Earth’s atmosphere and the physical processes that occur within it. Flight academies teach Meteorology since it is extremely important for student pilots because the atmosphere is the medium through which the aircraft moves. It is essential to know what conditions are present along a route, and knowledge of the processes in which weather forms is useful for predicting what conditions may occur during flight

Atmosphere refers to the gaseous envelope that surrounds the Earth. It is held to the Earth by the force of gravity. This gaseous envelope moves with the rotation of the Earth and extends from the surface of the planet up to the boundary of space. It acts as a fluid, is a poor conductor of head and only supports life in the lower levels.

Due to the changing volume of air in different levels of the atmosphere, variations are found both horizontally and vertically in the following properties:

• Pressure
• Temperature
• Density
• Humidity

A big part of flight training focuses entirely on aviation meteorology with all its aspects by breaking down the atmosphere into layers of specific dimensions and analyzing the weather phenomena that exist within each level.

Composition of the atmosphere

The density of the atmosphere decreases with altitude. This does not affect the composition of the atmosphere. The meaning composition is the ratios at which gases exist in the atmosphere. As the altitude increases, the ratios of gases in the air remain the same but the quantity of the gas decreases with altitude due to the decreasing air temperature. The gas ratios in the atmosphere are as follows:

• Nitrogen 78%
• Oxygen 21%
• Argon 0.9%
• Carbon Dioxide 0.1%

The Structure of the Atmosphere

There are five layers in the atmosphere starting from the surface of Earth upwards and they are named as follows:

• Troposphere
• Stratosphere
• Mesosphere
• ionosphere
• Exosphere

The troposphere extends from the surface up to average height of 11 km. within this layer, temperature decreases 2 degrees Celsius per 1,000 feet and pressure drops by 1 inch of mercury per 1,000 feet. This layer is of an extreme importance to everyone involved in the aviation world due to it holding all the water vapor in the atmosphere and being the layer where most flying occurs.

The Troposphere

In the troposphere, air masses are constantly moving around from high pressure to low pressure areas which causes major weather phenomena from different types of clouds and storms to drastic changes in temperature which makes it an essential part of the meteorological studies a student pilot has to complete in his/her respective flight academy.

The Tropopause is the upper boundary of the troposphere which separates the troposphere from the stratosphere. At the tropopause, the temperature ceases to decrease with decreasing height and it is also the height which the ozone layer exists. The height of the tropopause varies between 26,000 feet and 52,000 feet depending on the location on the planet and the time of the year.

The stratosphere

The stratosphere extends from the tropopause to approximately 50 km above the surface of the Earth. Some flying occurs in the lower parts of the stratosphere, so the combination of the troposphere and lower parts of the stratosphere is therefore often referred to as the aviation atmosphere.

This layer is relatively stable. Initially, the temperature remains constant and then starts to increase so that is around 0 degrees Celsius at the top of the layer. This is due to the absorption of ultra violet radiation by ozone in the lower layers of the stratosphere and the retransmission of this radiation as infra-red heat. The concentration of ozone varies with latitude, being greater over the poles than the equator. This layer has very little vertical movement concerning cloud formation but very strong horizontal winds than can very beneficial to pilots.

The remaining layers carry very little to no weather, and are not usable at all by any commercial aviation aircrafts except for the traveling of GPS transmission and that will be covered at a later stage.

Please refer to figure 01 below which serves as a summary to the structure of atmosphere.