The stratosphere is an atmospheric layer made up of stratified temperature layers, with warm layers of air high in the sky and cool layers of air low in the sky, close to the Earth's planetary surface. The stratosphere is the second layer of the Earth's atmosphere, located above the troposphere and below the mesosphere. Ozone, an unusual type of oxygen molecule that is relatively abundant in the stratosphere, heats this layer by absorbing energy from the Sun's incoming ultraviolet radiation. In this article, you will read about the stratosphere in detail which is important for the IAS exam preparation.

Stratosphere

• The stratosphere lies slightly above the troposphere and below the mesosphere, which is the second primary layer of the Earth's atmosphere.
• The lower edge of the stratosphere can reach 20 km near the equator, 10 km at midlatitudes, and 7 km at the poles. As a result, the stratosphere is closest to the poles in terms of altitude.
• The height of the bottom of the stratosphere varies with latitude and with the seasons.
• It holds a large portion of the ozone in the atmosphere.

Temperature Stratification in the Stratosphere

• The temperature of the stratosphere is stratified, with warmer layers rising up and cooler layers lowering down.
• The temperature at the top of the stratosphere is around 3°C, just below the freezing point of water.
• The summer pole has the greatest temperature, while the winter pole has the lowest.
• The temperature has a tendency to rise in the stratosphere because of the presence of the Ozone.
• The air is extremely rarefied, with only eight ozone molecules per million.
• Temperatures at the stratopause (another boundary between troposphere and stratosphere), which is about 50 km above Earth, are about the same edge temperature found on Earth's surface, although little of the heat can be transferred because the air is so thin.

Why are there no Vertical Winds in the Stratosphere?

• In the stratosphere, the temperature rises with altitude, it is a fairly stable environment where the air does not tend to overturn vertically. Therefore, in the stratosphere, vertical winds are nearly non-existent.
• In comparison to the atmosphere, where vertical wind speeds can reach several metres per second, vertical wind speeds in the stratosphere rarely exceed a few millimetres per second.
• As a result, air transfer from the bottom of the stratosphere takes a long time unless there is a thrust of gases, such as during highly explosive volcanic eruptions.
• Materials that get into the stratosphere can stay there for a long period due to the lack of vertical convection in the stratosphere for example CFCs (chlorofluorocarbons), or ozone-depleting compounds.
• Large volcanic eruptions and large meteorite impacts can throw aerosol particles into the stratosphere, where they might remain for months or years, causing global climate change. Rocket launches inject exhaust gases into the stratosphere, producing uncertain consequences.

Aviation & Jet Streams in Stratosphere

• The severe weather changes that occur below in the Troposphere do not affect the Stratosphere.
• Hence, aircraft are flown in the lower stratosphere, just above the tropopause, during the cruise phase of their flights; in this region, clouds and significant weather perturbations are usually absent.
• Jetliners, on the other hand, must contend with another threat in the stratosphere i.e., jet streams.
• Jet streams are horizontal air currents with high velocity. The primary jet streams are located in the tropopause.
• For aviation, the location of the jet stream is critical. Jet streams aren't necessarily bad for flying. They are advantageous and commercially employed because they cut travel time and fuel consumption.

Ozone Layer in Stratosphere

• The Ozone layer is contained within the stratosphere.
• Ozone concentrations in this layer range from 2 to 8 parts per million, which is substantially higher than in the lower atmosphere but still quite low when compared to the primary atmospheric constituents.
• It is mostly found in the lower stratosphere, between 15 and 35 kilometres. However, the thickness varies seasonally and geographically.
• The stratosphere contains approximately 90% of the ozone in our atmosphere.
• The ozone in this area absorbs high-intensity ultraviolet energy waves from the Sun and breaks them down into oxygen and diatomic oxygen.
• Due to UV light bombardment and destruction of both ozone and diatomic oxygen, atomic oxygen is found in abundance in the high stratosphere.
• The sun's UV light is absorbed by the ozone layer, which transforms it into heat and chemical energy. It is this activity that is causing the temperature to rise.
• The layer does not have a consistent thickness. The equator has the highest elevation, while the poles have the lowest.
• Ozone in the stratosphere protects humans from skin cancer and other health problems by absorbing harmful UV rays.
• However, chemicals (such as CFCs, freons, and halons) that are used in refrigerators, spray cans, and fire extinguishers have lowered the amount of ozone in the stratosphere, resulting in the so-called "Antarctic ozone hole."

Influence of Waves and Tides in Stratosphere

• The stratosphere is influenced by various types of waves and tides in the atmosphere.
• Some waves and tides transport energy from the troposphere to the stratosphere, while others transport energy from the stratosphere to the mesosphere.
• The movement of air in the stratosphere is influenced by waves and tides, and this layer of the atmosphere can also be heated regionally.

Conclusion

The stratosphere stands as a critical layer of Earth's atmosphere, characterized by its stratified temperature structure and the presence of the vital ozone layer. Understanding the dynamics of the stratosphere—from the variation in temperature and the absence of vertical winds to the influence of waves and tides—is essential for various fields, including aviation and environmental studies. The role of the stratosphere in filtering ultraviolet radiation through the ozone layer highlights its significance in protecting life on Earth, despite the threats posed by human-made pollutants like CFCs.

FAQs

Question. What is the stratosphere?

Question. What are the key features of the stratosphere?

Question. Why is the ozone layer important in the stratosphere?

Question. How does the stratosphere differ from the troposphere?

Question. What is the significance of the stratosphere for aviation?

MCQs

1. Which of the following is found in the stratosphere?

A) Weather systems

B) Ozone layer

C) Clouds and rain

D) Water vapor

2. At what altitude does the stratosphere begin?

A) 5 km

B) 10 km

C) 20 km

D) 50 km

3. In which layer of the atmosphere does temperature increase with altitude?

A) Troposphere

B) Mesosphere

C) Stratosphere

D) Thermosphere

4. Which atmospheric layer is directly above the stratosphere?

A) Troposphere

B) Mesosphere

C) Thermosphere

D) Exosphere

5. Why do aircrafts typically fly in the lower stratosphere?

A) The air is denser

B) The temperature is lower

C) There is less turbulence

D) Weather systems are stronger

GS Mains Questions and Model Answers

Q1: Explain the role of the stratosphere in regulating Earth's climate.

Answer: The stratosphere plays a key role in regulating Earth's climate by absorbing ultraviolet radiation from the Sun through the ozone layer. This absorption helps to warm the stratosphere, and it also protects living organisms from harmful UV rays. Changes in the stratosphere, such as ozone depletion, can lead to significant climate disruptions, affecting weather patterns and ecosystems.

Q2: Discuss the environmental challenges posed by the depletion of the ozone layer in the stratosphere.

Answer: Ozone depletion in the stratosphere allows more ultraviolet radiation to reach Earth's surface, which can cause skin cancer, cataracts, and weaken immune systems in humans, as well as disrupt plant and marine ecosystems. It also leads to environmental changes like crop damage, ecosystem imbalances, and threats to biodiversity. The Montreal Protocol has been instrumental in reducing the use of ozone-depleting substances.

Q3: How does the stratosphere interact with other atmospheric layers in terms of weather systems?

Answer: The stratosphere and troposphere are separated by the tropopause, a boundary where the weather systems occur, such as clouds and storms, within the troposphere. The stratosphere's stable and temperature-increasing nature means it has little to no role in weather patterns, but it influences jet streams and atmospheric circulation patterns, which can affect surface weather. Moreover, disruptions in the stratosphere, like sudden stratospheric warming, can impact weather in the lower atmosphere.

Previous Year Questions on the Stratosphere

1. UPSC CSE 2017

Question: "Explain the role of ozone in the stratosphere and its impact on human health and the environment."

Answer: Ozone in the stratosphere absorbs the majority of the Sun's harmful ultraviolet radiation, preventing it from reaching the Earth's surface. This protective layer is essential for human health, as increased exposure to UV radiation can cause skin cancer and cataracts. It also affects plant growth and marine life. The depletion of the ozone layer due to human activity has led to increased UV radiation, impacting both human health and ecosystems.

2. UPSC CSE 2020

Question: "What is the importance of studying the different layers of Earth's atmosphere for understanding climate change?"

Answer: Understanding the different layers of the atmosphere, including the stratosphere, is crucial for studying climate change. The stratosphere regulates the Earth's temperature by absorbing UV radiation. Disruptions in the stratosphere, such as ozone depletion, can alter weather patterns and contribute to climate change. Studying atmospheric layers allows scientists to predict long-term climate trends and understand the effects of human activities like pollution and deforestation on global weather patterns.