What is the Atmosphere?

The Earths atmosphere is made up of many different gases and is defined by several different layers.

The layers that comprise our earth atmosphere are determined by the temperature changes that occur throughout the layers.

Although the air above is closer to the sun, it does not absorb the suns heat as one would think. In fact, the earths atmosphere is heated predominantly from the surface! This means the surface of the earth will always be warmer than the air above. We all know this because we understand that if we were to climb a tall mountain, the temperature would become colder the further we climbed.

Temperatures have been recorded from all around the world and at all different altitudes. From these measurements global averages of temperature, pressure and air density have been provided. These figures are used as a 'yard stick' in the study of meteorology and aircraft performance. Meaning they can be used as a starting point to compare current conditions.

It is called the "International Standard Atmosphere" or ISA for short. Details of ISA will be covered in another course but what you must know for now is this:

• Temperature decreases with altitude i.e. the further you climb into the sky the colder it will get
• There are altitudes where temperature STOPS decreasing or PAUSES (this is called an isotherm). i.e. continue to climb pass this altitude and the temperature will remain the same.
• These PAUSES are only temporary and mark the boundary layers within our atmosphere.

The layers of the Atmosphere

The Troposphere

The Troposphere is the layer that touches the ground. This is where the majority of our weather happens, where we live and where we fly many of our aircraft. The top of the troposphere is marked by a pause in the reduction of temperature (an isotherm) - this first isotherm is called the Tropopause.

The Stratosphere

Above The Troposphere and Tropopause is the Stratosphere. Very few aircraft fly in the stratosphere - it used to see spaceships only or fancy hi-tech military aircraft however nowadays many commercial airliners will fly in the lower stratosphere to avoid weather and turbulence. The top of the stratosphere is again marked with a pause in temperature called the Stratopause.

The Mesosphere

No cloud, no aircraft, maybe the odd spaceship. ;)

The Thermosphere

No cloud, no aircraft.

The Exosphere

Finally there is the Exosphere, which we might as well call space as there is very little up there and it is quite hard to determine where the exosphere stops and space starts.

Pilots are expected to be able to name the atmospheric layers and pauses in the correct order as well as have a basic understanding of temperature changes throughout each layer.

Grab a pen and paper and watch the following video prepared for you. Recommended that you make a copy of this in your study notes.

Ozone Layer

An ozone is a gas made up of 3 oxygen atoms (O3). It is created through a chemical reaction, where oxygen atoms are split by the suns radiation and then rejoined into three atoms of oxygen.

From the previous video, you can identify two layers which make up the ozone layer, however, 99% of the ozone layer is found in the Stratosphere.

The ozone layer helps reduce suns ultra-violet light from reaching the earth surface. It is an essential part of the atmosphere, as it prevents our skin from burning and many other harmful medical conditions that can affect animals and plants. The earths surface would become sterilised without the layer of ozone protecting it from above.

We live in a world seemingly balanced by the uneven heat of the sun, heating during the day and cooling during the night. This natural balance is what provides us with seasons and 'almost' predictable weather patterns.