Mesosphere
Why in News?
It is recently in the news due to its role as a "sentinel" for climate change and new experimental technologies designed to explore it. The Mesosphere (the "middle sphere") is the third layer of Earth's atmosphere, situated between the stratosphere and the thermosphere.
Physical Characteristics
- Altitude: Extends from about 50 km to 85–100 km above the Earth's surface.
- Temperature: It is the coldest place on Earth. Temperatures decrease with height, reaching as low as -90°C to -143°C at the "mesopause" (the upper boundary).
- Pressure: The air is extremely thin; pressure at the top is only 1/100,000th of the pressure at sea level.
Key Phenomena
- Meteor Shield: This is the layer where most meteors burn up. The friction with gas molecules creates enough heat to incinerate space debris, appearing as "shooting stars".
- Noctilucent Clouds (NLCs): These are the highest clouds in the atmosphere, made of ice crystals that form around meteoric dust. They "glow" electric blue at twilight because they are high enough to reflect sunlight even after the sun has set on the ground.
- Transient Luminous Events (TLEs): The mesosphere hosts exotic electrical discharges like Red Sprites and ELVES, which occur above massive thunderstorms in the troposphere.
Composition & Dynamics
- Meteoric Smoke: The disintegration of meteors leaves behind a layer of metal atoms like sodium, iron, and potassium.
- Atmospheric Waves: Strong winds and "gravity waves" transfer energy from the lower atmosphere to the mesosphere, influencing global circulation and weather patterns.
- Chemical Transition: It is a transition zone where the air stops being a uniform mixture and begins to separate into layers based on molecular mass.
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