Layers of Atmosphere
The Different Layers of The Atmosphere
The atmosphere can be divided into layers based on its temperature, as shown in the figure below. These layers are the troposphere, the stratosphere, the mesosphere and the thermosphere. A further region, beginning about 500 km above the Earth’s surface, is called the exosphere.
The red line in the figure below shows how temperature varies with height (the temperature scale is given at the bottom of the diagram). The scale on the right shows the pressure. For example, at a height of 50 km, the pressure is only about one-thousandth of the pressure at the ground.
Earth’s atmosphere has a series of layers, each with its own specific traits. Moving upward from ground level, these layers are named the troposphere, stratosphere, mesosphere, thermosphere and exosphere. The exosphere gradually fades away into the realm of interplanetary space.
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The troposphere is the lowest layer of our atmosphere. Starting at ground level, it extends upward to about 10 km (6.2 miles or about 33,000 feet) above sea level. We humans live in the troposphere, and nearly all weather occurs in this lowest layer. Most clouds appear here, mainly because 99% of the water vapour in the atmosphere is found in the troposphere. Air pressure drops, and temperatures get colder, as you climb higher in the troposphere. Layers Of Atmosphere
The next layer up is called the stratosphere. The stratosphere extends from the top of the troposphere to about 50 km (31 miles) above the ground. The infamous ozone layer is found within the stratosphere. Ozone molecules in this layer absorb high-energy ultraviolet (UV) light from the Sun, converting the UV energy into heat. Unlike the troposphere, the stratosphere actually gets warmer the higher you go. Layers Of Atmosphere
That trend of rising temperatures with altitude means that air in the stratosphere lacks the turbulence and updrafts of the troposphere beneath. Commercial passenger jets fly in the lower stratosphere, partly because this less-turbulent layer provides a smoother ride. The jet stream flows near the border between the troposphere and the stratosphere.
Above the stratosphere is the mesosphere. It extends upward to a height of about 85 km (53 miles) above our planet. Most meteors burn up in the mesosphere. Unlike the stratosphere, temperatures once again grow colder as you rise up through the mesosphere. The coldest temperatures in Earth’s atmosphere, about -90° C (-130° F), are found near the top of this layer. The air in the mesosphere is far too thin to breathe; air pressure at the bottom of the layer is well below 1% of the pressure at sea level and continues dropping as you go higher. Layers Of Atmosphere
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The layer of very rare air above the mesosphere is called the thermosphere. High-energy X-rays and UV radiation from the Sun are absorbed in the thermosphere, raising its temperature to hundreds or at times thousands of degrees. However, the air in this layer is so thin that it would feel freezing cold to us! In many ways, the thermosphere is more like outer space than a part of the atmosphere.
Many satellites actually orbit Earth within the thermosphere! Variations in the amount of energy coming from the Sun exert a powerful influence on both the height of the top of this layer and the temperature within it. Because of this, the top of the thermosphere can be found anywhere between 500 and 1,000 km (311 to 621 miles) above the ground.
Temperatures in the upper thermosphere can range from about 500° C (932° F) to 2,000° C (3,632° F) or higher. The aurora, the Northern Lights and Southern Lights occur in the thermosphere.
The ionosphere is not a distinct layer like the others mentioned above. Instead, the ionosphere is a series of regions in parts of the mesosphere and thermosphere where high-energy radiation from the Sun has knocked electrons loose from their parent atoms and molecules. The electrically charged atoms and molecules that are formed in this way are called ions, giving the ionosphere its name and endowing this region with some special properties.
Although some experts consider the thermosphere to be the uppermost layer of our atmosphere, others consider the exosphere to be the actual “final frontier” of Earth’s gaseous envelope. As you might imagine, the “air” in the exosphere is very, very, very thin, making this layer even more space-like than the thermosphere. In fact, the air in the exosphere is constantly – though very gradually – “leaking” out of Earth’s atmosphere into outer space. There is no clear-cut upper boundary where the exosphere finally fades away into space.
Different definitions place the top of the exosphere somewhere between 100,000 km (62,000 miles) and 190,000 km (120,000 miles) above the surface of the Earth. The latter value is about halfway to the Moon!
The exosphere is almost a vacuum. The “air” is very, very thin there. When air is thin, it doesn’t transfer much heat to objects in the air, even if the air is very, very hot.
One definition scientists use for temperature is the average speed of the molecules or atoms in a gas. When the particles are moving very fast, the temperature is hot. When particles are bouncing around more slowly, the temperature is cooler. The particles in the exosphere are moving very quickly, so the temperature there is quite hot. However, the exosphere would feel quite cold to us. How can that be? Since the “air” is so thin in the exosphere – it is almost a vacuum – there are very, very few particles. We feel warmth when particles hit our skin and transfer heat energy to us. There are too few particles in the exosphere to transfer much energy, even though each particle is quite “hot” itself. layers of atmosphere
Objects in the exosphere are hot if lots of sunlight shines on them. Sunlight is very, very bright up there, so objects in the sunshine heat up quickly. However, objects in the shade can get really, really cold. For example, one side (the sunny side) of a satellite might be very hot, while the other side (in the shade) might be freezing cold.
The earth behaves like a huge magnet. It traps electrons (negative charge) and protons (positive), concentrating them in two bands about 3,000 and 16,000 km above the globe – the Van Allen “radiation” belts. This outer region surrounding the earth, where charged particles spiral along the magnetic field lines, is called the magnetosphere.