Under normal conditions, temperature usually decreases with increase in altitude in the troposphere at a rate of 1 degree for every 165 metres. This is called normal lapse rate. But on some occasions, the situation gets reversed and temperature starts increasing with height rather than decreasing. This is called temperature inversion.

Favourable Conditions for Temperature Inversion

1. Long winter nights: Loss of heat by terrestrial radiation from the ground surface during night may exceed the amount of incoming solar radiation.
2. Cloudless and clear sky: Loss of heat through terrestrial radiation proceeds more rapidly without any obstruction.
3. Dry air near the ground surface: It limits the absorption of the radiated heat from the Earth’s surface.
4. Slow movement of air: It results in no transfer or mixing of heat in the lower layers of the atmosphere.
5. Snow covered ground surface: It results in maximum loss of heat through reflection of incoming solar radiation.

Types of Temperature Inversion

Temperature inversion occurs in several conditions ranging from ground surface to great heights. Thus there are several kinds of temperature inversions. The following are classified on the basis of relative heights from the earth’s surface at which it occurs and the type of air circulation:

1. Non-Advectional
2.   Radiation Inversion (Surface Temperature Inversion)
3.           Occurs during clear and calm nights when the ground loses heat rapidly by radiation.
4.           The air in contact with the cold surface becomes cooler than the air above it.

                                          iii.            Common in higher latitudes and during winter nights in middle and lower latitudes.

1.           If surface temperature falls below dew point, fog or frost may form.
2. Subsidence Inversion (Upper Surface Temperature Inversion)
3.           Develops when air descends over a wide area, gets compressed and warms adiabatically.
4.           Upper air becomes warmer than the air below, creating an inversion.

                                          iii.            Common over subtropical oceans and continental interiors in winter, associated with high-pressure systems.

1.           It is also called upper surface temperature inversion because it takes place in the upper parts of the atmosphere.
2. Advectional
3.   Valley inversion in intermontane valley
4.           Occurs in mountain valleys and intermontane basins.
5.           Cold, dense air flows downslope at night and accumulates at valley floors.

                                          iii.            Results in colder air below and warmer air above, producing inversion conditions.

1. Frontal or Cyclonic inversion
2.           Forms when warm and cold air masses meet at a front.
3.           Warm air rises over denser cold air, creating an inversion with a steep slope.

                                          iii.            Common in temperate regions and associated with cyclonic activity and precipitation.

1.           A frontal inversion is unstable and is destroyed as the weather changes.

Temperature Inversion Significance

1. Weather phenomena: Temperature Inversions can lead to the formation of fog, frost, and dew, affecting visibility and daily weather conditions. (Eg – Formation of fog in valleys like California’s San Joaquin Valley)
2. Air pollution: These inversions act as a lid on vertical air movement, trapping pollutants and smoke near the surface, causing smog in urban and industrial regions (Eg – In cities like Los Angeles and Beijing). This can worsen respiratory and heart-related health problems.
3. Agriculture: Radiation inversions may cause frost damage to crops, though in some cases they can protect crops by limiting air mixing. (Eg – Vineyards in Napa Valley affected by this)
4. Aviation: Creates turbulence, poor visibility and altered aircraft performance, posing risks to flight operations.
5. Climate and energy use:
6.   By changing temperature distribution near the ground, inversions influence heating and cooling requirements, affecting energy consumption patterns.
7.   Studying inversions is essential for understanding regional climate, especially in valleys or basins where persistent inversions are common.
8. Disaster management: It helps to trap wildfire smoke, worsening air quality and complicating firefighting efforts. (Eg – As seen in California and Australia wildfire seasons)
9. Atmospheric stability: Suppresses convection, reduces cloud formation and may prolong dry or stagnant weather conditions. (Eg – in arctic and antarctic regions)

Temperature inversion is a significant atmospheric phenomenon marked by a reversal of the normal lapse rate, leading to stable air conditions. While it plays a role in local weather processes, its broader implications for air quality, agriculture, aviation and human health make it an important concept in climatology and environmental studies.