Temperature Inversion: Causes, Types and Effects

Temperature inversion is a curious atmospheric occurrence that flips our usual understanding of temperature changes with altitude. Normally, as we go higher, it gets cooler, but in certain conditions, like on a still, clear winter night, this trend reverses. During such nights, the Earth loses heat absorbed during the day, causing the ground to become cooler than the air above it by dawn. In polar regions, temperature inversion happens regularly throughout the year.

Phenomenon of Temperature Inversion

• Definition: It is a reversal of the normal behaviour of temperature (temperature drops as altitude increases) in the troposphere, in which a layer of cool air at the surface is overlain by a layer of warmer air.
• Ideal Conditions for Temperature Inversion:
  • Long winter night (outgoing radiation is greater than the incoming radiation);
  • Clear and cloudless sky;
  • Still air (no/slow horizontal movement of air) which avoids mixing of air;
  • Dry air near the ground surface
  • In polar regions, temperature inversion is normal throughout the year.
• Effects of Surface Temperature Inversion: 
  • The lower atmosphere becomes stable; causing smoke, dust, and other particles to get trapped beneath the inversion layer, leading to formation of dense fog.
  • In hilly and mountainous terrains, inversion is due to a process called air drainage (downward flow of cold air from mountain slopes to valleys during night). 
  • It acts as a protective shield for plants, saving them from frost damage.

Types of Temperature Inversion

• Surface Temperature Inversion: Takes place on the layers in contact with the surface through the process of conduction. 
  • Fog formation is possible if the temperature of surface air drops below its dew point. 
  • Common in the higher latitudes; In lower & middle latitudes it occurs during cold nights and gets destroyed during the daytime.
• Valley Inversion: Takes place in hills and mountains due to air drainage. 
  • Cold air (heavy and dense) produced during the night, flows under the influence of gravity and moves down the slope to pile up in valley bottoms with warm air above. 
  • This is called air drainage. 
  • Protects plants from frost damages
• Frontal Inversion (Advectional type): Occurs when a cold air mass undercuts a warm air mass and lifts it aloft. 
  • It is unstable and is destroyed as the weather changes.

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Effects of Temperature Inversion

• Surface temperature inversions can have significant effects on the atmosphere and the environment, leading to phenomena like fog and frost protection in certain terrains. 
• Stability of the Lower Atmosphere: Lower Layer Trap in Inversions
  • During a surface temperature inversion, the lower atmosphere becomes stable. 
  • This stability is due to a layer of warmer air being overlaid by a layer of cooler air near the Earth’s surface.
  • This stable condition traps smoke, dust, and other airborne particles beneath the inversion layer.
• Airborne Particle Trapping: 
  • Particles like smoke, dust, and pollutants are confined to the lower atmosphere and cannot rise through the inversion layer.
  • This results in the spread of these particles throughout the lower atmosphere.
• Dense Fog Formation: Surface temperature inversions are often associated with the formation of dense fog, especially on winter mornings.
  • Fog forms as the moisture in the trapped, cool air condenses, creating reduced visibility and high humidity at the surface.
• Dispersal as the Sun Rises: With the arrival of daylight and solar heating, the inversion layer typically disperses.
  • As the Earth’s surface warms, the trapped cold air rises, mixing with the warmer air above.
• Air Drainage in Hilly and Mountainous Terrains: In hilly and mountainous areas, surface temperature inversions can also occur due to a process called air drainage.
  • At night, cold air forms over the slopes of hills and mountains. 
  • This dense, cold air behaves like a liquid, flowing downward into valleys and low-lying areas.
  • Above this cold layer, warmer air remains.
• Frost Protection: The downward flow of cold air, known as air drainage, acts as a protective shield for plants in valleys and low areas.
  • This downward movement of cold air can help protect plants from frost damage, as the cold air prevents the radiational cooling of the ground.

Conclusion

Temperature inversions can lead to stable atmospheric conditions, the trapping of airborne particles, fog formation, and protective effects like frost protection in specific terrains. The dispersal of the inversion typically occurs as the sun rises and warms the Earth’s surface, promoting air mixing.

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