Temperature Inversion | 29 Aug 2020

Meaning

• 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 situations get reversed and temperature starts increasing with height rather than decreasing. This is called temperature inversion.
• Temperature inversion: It is a reversal of the normal behavior of temperature in the troposphere. Under this meteorological phenomenon a layer of warm air lies over the cold air layer.
  
  • It is caused in stac atmospheric conditions while some times, it occurs due to horizontal or vertical movement of air.
  • Temperature inversion is usually of short duration but quite common nonetheless.

Favourable Conditions for Temperature Inversion

• Long winter nights: Loss of heat by terrestrial radiation from the ground surface during night may exceed the amount of incoming solar radiation.
• Cloudless and clear sky: Loss of heat through terrestrial radiation proceeds more rapidly without any obstruction.
• Dry air near the ground surface: It limits the absorption of the radiated heat from the Earth’s surface.
• Slow movement of air: It results in no transfer or mixing of heat in the lower layers of the atmosphere.
• 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:
• Non-Advectional
  
  • Radiation Inversion (Surface Temperature Inversion)
    
    • Surface temperature inversion develops when air is cooled by contact with a colder surface until it becomes cooler than the overlying atmosphere; this occurs most often 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.
    • It is very common in the higher latitudes. In lower and middle latitudes, it occurs during cold nights and gets destroyed during day time.
  • Subsidence Inversion (Upper Surface Temperature Inversion)
    
    • When a widespread layer of air descends, it is compressed and heated by the resulting increase in atmospheric pressure, and as a result the lapse rate of temperature is reduced.
    • The air at higher altitudes becomes warmer than at lower altitudes, producing a temperature inversion. This type of temperature inversion is called subsidence inversion.
    • It is very common over the northern continents in winter (dry atmosphere) and over the subtropical oceans; these regions generally have subsiding air because they are located under large high-pressure centers.
    • It is also called upper surface temperature inversion because it takes place in the upper parts of the atmosphere.

• Advectional
  
  • Valley inversion in intermontane valley
    
    • In high mountains or deep valleys, sometimes, the temperature of the lower layers of air increases instead of decreasing with elevation along a sloping surface.
    • Here, the surface radiates heat back to space rapidly and cools down at a faster rate than the upper layers. As a result the lower cold layers get condensed and become heavy.
    • The sloping surface underneath makes them move towards the bottom where the cold layer settles down as a zone of low temperature while the upper layers are relatively warmer.
    • This condition, opposite to normal vertical distribution of temperature, is known as Temperature Inversion.
  • Frontal or Cyclonic inversion
    
    • When the warm and cold fronts meet, then the warm front rises up and being heavier the cold front sinks down. It results in formation of Frontal Inversion.
    • It has considerable slope, whereas other inversions are nearly horizontal. It often takes place in the temperate zone and causes cyclonic conditions which result in the precipitation in different forms.
    • A frontal inversion is unstable and is destroyed as the weather changes.

Effect

• Temperature inversion determines the precipitation, forms of clouds, and also causes frost due to condensation of warm air due to its cooling.
  
  • Dust particles hanging in the air: Due to inversion of temperature, air pollutants such as dust particles and smoke do not disperse on the surface.
  • Stops the movement of air: It causes the stability of the atmosphere that stops the downward and upward movement of air.
  • Less rainfall: Convection clouds can not move high upwards so there is less rainfall and no showers. So, it causes a problem for agricultural productivity.
  • Lower visibility: Fog is formed due to the situation of warm air above and cold air below, and hence visibility is reduced which causes disturbance in transportation.
  • Thunderstorms and tornadoes: Intense thunderstorms and tornadoes are also associated with inversion of temperature because of the intense energy that is released after an inversion blocks an area’s normal convention patterns.
  • Diurnal variations in temperature tend to be very small.