Earth’s atmosphere has five major layers. These are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The stratosphere is next to the troposphere and extends up to 50 kilometers. In this region, the temperature rises gradually up to minus two degrees Celcius. The presence of ozone in this region is responsible for temperature rise.
What happens in the stratosphere?
The stratosphere is the second layer in the atmosphere, stretching from about 10 kilometers to 50 kilometers. There’s no large-scale vertical movement of air masses in the stratosphere. The name stratosphere comes from the fact that it has many different air layers on top of one another that don’t communicate.
For this reason, commercial airliners typically fly in the lower stratosphere. They’re flying above the storms of the troposphere and getting a boost from the strong winds. Because of all of this, the stratosphere is quite quiescent.
Temperature: The temperature is -56°C to -2°C. It is due to the absorption of ultraviolet radiation by ozone. When ozone absorbs this ultraviolet radiation, it increases the temperatures. It differed from the troposphere because of its temperature profile. How did the temperature change with height?
In the troposphere, temperatures decrease with altitude, whereas temperatures increase without altitude in the stratosphere. If an object’s thermal energy increases, its temperature must also increase. This happens when the amount of energy flowing into an object is greater than the energy flowing.
In this case, that form of energy is thermal energy. If the amount of energy flowing out of an object is greater than the amount of energy flowing into it, its temperature must decrease. The energy imbalance in the flow in and out must be converted into a change in another energy form. That change of form of energy is a decrease in thermal energy.
Height: Its height is 11 km to 50 km above the troposphere.
Pressure: 1 millibar (approximately equal to 0.75 mm of mercury at 0 °C, or 0.03 inch of mercury at 32 °F).
Airflow: An inevitable stratospheric warming begins 50 kilometers above the surface in the very high-altitude jet stream. A wavy light disturbance begins to disrupt the jet stream. As the wave grows, it reaches a point where it turns over and breaks, like a wave hitting a beach. At this point, the wave to the jet stream pushes the jet stream in the opposite sense. So it pushes the air against the jet stream’s flow, and it weakens the jet stream.
At this point, the air starts to fall into the Arctic. Also, It’s all falling into the Arctic and getting squashed. So there’s no heating going on. Winds from the east at high altitudes from the lower atmosphere can no longer propagate into that part of the atmosphere.
It turns out that waves can only propagate when the winds are from the West. So they see this easterly region at a high altitude. They push the air from the east, and the whole thing moves slightly downwards. The next bunch of waves comes up. They break on the bottom side of this easterly wind, bringing it down even further. The weather is occurring in the lower atmosphere.
Composition: The ozone is the main component of the stratosphere. The quantity of ozone is maximum at 30 km. When the height increases, then the concentration of ozone increases. When molecular oxygen absorbs ultraviolet radiation, it produces atomic oxygen.
Atomic oxygen immediately reacted with molecular oxygen to produce ozone. Therefore, it is also known as the ozonosphere. All the ozone (90%) in the atmosphere is found in the stratosphere. It is formed when sunlight breaks down molecular oxygen into oxygen atoms (O) in the stratosphere.
Ozone depletion in the stratosphere: In the atmosphere, the ozone exists in two forms: good and harmful ozone. Bad ozone is formed in the troposphere that harms plants and animals. There is good ozone that surgeon is found in the upper part of the atmosphere called the stratosphere.
It acts as a shield absorbing ultraviolet radiation from the Sun. UV rays are highly harmful to live organisms. Since DNA and proteins of living organisms preferentially absorb easy rays. It is high-energy and breaks the chemical bonds within these molecules.
Dobson units measure the ozone’s thickness in a column of air from the ground to the atmosphere’s top. Ozone gas is continuously formed by UV rays on molecular oxygen and degraded into molecular oxygen in the stratosphere. There should be a balance between the production and degradation of ozone in the stratosphere.
The balance has been disrupted due to the enhancement of ozone degradation by chlorofluorocarbons (CFCs). CFCs find wide use as refrigerants. It discharges in the lower part of the atmosphere, moves upward, and reaches the stratosphere.
The ozone layer is created by the Chapman cycle.
Step 1: An oxygen molecule is photolyzed by solar radiation, creating two oxygen radicals:
hν + O2→ 2O
Step 2: Oxygen radicals then react with molecular oxygen to produce ozone:
O2 + O.→ O3
Step 3: Ozone then reacts with additional oxygen radicals to form molecular oxygen:
O3 + O.→ 2O2
Step 4: Ozone can also be recycled into molecular oxygen by reacting with a photon:
O3 + hν→ O2 + O
In the stratosphere, easy rays act on them, releasing chlorine atoms. Chlorine degrades ozone releasing molecular oxygen with these atoms acting merely as catalysts. Chlorine atoms are not consumed in the reaction. Hence whatever CFCs are added to the stratosphere, they have permanent and continuing effects on ozone levels.
The depletion is particularly marked over the Antarctic region. This has resulted in forming a large thin ozone layer called the ozone hole. UV radiation of wavelengths shorter than UVB is almost entirely absorbed by Earth’s atmosphere.
The ozone layer is intact, but UVB damages DNA and mutation may occur. It causes skin aging, skin cell damage, and various skin cancers. In the human eye, the cornea absorbs UVB radiation, and a high dose of UVB causes inflammation of Konya called snow blindness cataract.
The stratosphere is a relatively predictable part of the Earth’s atmosphere. We can predict what the stratosphere will be doing relatively far into the future, with few exceptions. Weather forecasts can predict future weather by generating stratospheric data and applying it to the surface.