What is Temperature Inversion?

• Normally, as altitude increases, temperature decreases at a rate of 1 degree for every 165 meters
• This is called normal lapse rate
• However, sometimes the temperature can increase with height instead of decreasing, known as temperature inversion
• Environmental lapse rate varies depending on location and time, especially in the lowest few hundred meters of the troposphere
• On average, temperature decreases by 6.5°C per 1000 meters (or 3.6°F per 1000 feet) in the troposphere
• This average temperature change rate is known as the average lapse rate or the average vertical temperature gradient within the troposphere.
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• A layer of warm air lies over the cold air layer during temperature inversion
• Temperature inversion can be caused by stagnant atmospheric conditions or by horizontal or vertical movement of air
• Temperature inversion is usually short-lived but common.

Effects of temperature inversion

• Temperature inversion has adverse effects on the society and economy of the region where it occurs
• Fog develops due to clouds in contact with the ground, and smog is formed in urban areas, which is a health hazard
• Reduced visibility due to the accumulation of dust and smoke particles can lead to road, railway, and air accidents
• Winter crops, orchards, and sugarcane crops can be seriously damaged due to temperature inversion
• In regions with a pronounced low-level inversion, convective clouds cannot grow high enough to produce showers
• Temperature inversions also affect diurnal variations in temperature, which tend to be very small.

Ideal Conditions For Temperature Inversion

1. Long nights, so that the outgoing radiation is greater than the incoming radiation.
2. Clear skies, which allow unobstructed escape of radiation.
3. Calm and stable air, so that there is no vertical mixing at lower levels.

Types of Temperature Inversion

• Frontal inversion:
  • It is caused by horizontal and vertical movement of air
  • Temperate cyclones are formed by the convergence of warm westerlies and cold polar air
  • Warm air overlies cold air, causing inversion of temperature and reversing the normal lapse rate
  • This type of inversion has a considerable slope, with high humidity and clouds present above it
  • This inversion is unstable and can be destroyed as the weather changes.
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• Temperature Inversion in Intermontane Valley (Air Drainage Type of Inversion):
  • Temperature inversion can occur when the temperature in lower layers of air increases instead of decreasing with elevation
  • This commonly occurs along a sloping surface, where the surface radiates heat back to space rapidly and cools down faster than upper layers
  • The lower cold layers become heavy and move towards the bottom, settling as a zone of low temperature, while upper layers remain warmer
  • This condition is opposite to the normal vertical distribution of temperature and is known as Temperature Inversion
  • In other words, the vertical temperature gets inverted during temperature inversion
  • This type of temperature inversion is strong in the middle and higher latitudes and can occur in regions with high mountains or deep valleys.
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• Ground Inversion (Surface Temperature Inversion):
  • Ground inversion occurs when surface air is cooled by contact with a colder surface until it becomes cooler than the overlying atmosphere.
  • This often happens on clear nights when the ground cools off rapidly by radiation.
  • If the temperature of surface air drops below its dew point, fog may result.
  • This kind of temperature inversion is very common in higher latitudes.
  • A surface temperature inversion in lower and middle latitudes occurs during cold nights and gets destroyed during the daytime.
  • This inversion disappears with sunrise.
  • The duration and height of surface inversion increase polewards.
  • Conditions required for ground surface inversion are long winter nights, cloudless calm skies, dry air and low relative humidity, calm atmosphere or slow movement of air, and snow-covered surface.
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• Subsidence Inversion (Upper Surface Temperature Inversion):
  • A subsidence inversion occurs when a widespread layer of air descends.
  • The compressed and heated layer of air results in an increase in atmospheric pressure and a reduction in the lapse rate of temperature.
  • If the air mass sinks low enough, a temperature inversion occurs where the air at higher altitudes becomes warmer than at lower altitudes.
  • Subsidence inversions are common over the northern continents in winter and over the subtropical oceans.
  • These regions generally have subsiding air because they are located under large high-pressure centers.
  • This temperature inversion is called upper surface temperature inversion because it takes place in the upper parts of the atmosphere.
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• Marine Inversion:
  • Cool, moist air from the ocean is blown onto land by prevailing westerly winds.
  • The cool air is denser and flows underneath the warmer, drier air over the basin, creating an inversion.
  • Marine inversions occur in places near large bodies of water, especially in the spring.
  • Air passing over large bodies of water is cooled by heat conduction to the water.
  • The cold air is blown inland and creates an inversion under the warmer air over the land.
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Economic Implications of Temperature Inversion

• The temperature at the valley bottom may reach below freezing point while the air at higher altitude is relatively warm.
• Frost can occur on trees at lower slopes due to the inversion of temperature.
• Air pollutants such as dust particles and smoke do not disperse in the valley bottoms due to the inversion of temperature.
• Houses and farms in intermontane valleys are usually situated along the upper slopes to avoid the cold and foggy valley bottoms.
• Coffee growers of Brazil and apple growers and hoteliers of mountain states of the Himalayas in India avoid lower slopes due to the inversion of temperature.
• Fog lowers visibility, affecting vegetation and human settlements.
• There is less rainfall due to stable conditions caused by the inversion of temperature.