What is Temperature Inversion?
The increase in air temperature with increasing altitude is called temperature inversion. On other hand, a temperature inversion occurs when a layer of warm air traps cool air near the Earth's surface.
This is exactly the opposite of what usually happens. Most of the time, the surface of the earth is warm during the day and as the altitude increases, the air temperature decreases, but in an inversion, the air becomes warmer with the increase in altitude.
Conditions for the formation of temperature inversion
1- Stable air
2- calm or light wind
3- Cool or cold night
4- clear sky
Types of temperature inversion
- Ground or radiation inversion(terrestrial radiation): This is the most common type of temperature inversion, which occurs over land and in cloudless and windless nights.
During the night, the earth loses its heat through terrestrial radiation and cools the surrounding air, as a result, the lower part of the atmosphere becomes colder than the upper air and causes a temperature inversion.
- Turbulence or vertical advection inversion: This type of inversion occurs when a layer of stagnant air sits atop a layer of turbulent air. The turbulent layer transports heat downward, cooling its upper layer through a process called vertical mixing. However, the layer of stagnant air remains unmixed and is therefore warmer than the air below it.
- Subsidence inversion: When a large layer of air descends due to high pressure, it warms up rapidly(adiabatically), while the air at lower altitudes remains cooler, creating a subsidence inversion.
- Frontal inversion: This type of inversion occurs when warm and cold air masses meet. The cold air is denser than the warm air, so it forces the warm air to rise. This can create a temperature inversion, with the warm air above the colder air.
The effect of temperature inversion in aviation
Temperature inversion is one of the important factors in the formation of low clouds, smog, fog, lack of precipitation and impaired visibility. Here's how temperature inversions affect aviation and our environment:
- Poor visibility: Due to the absence of wind and cold air being trapped under the warm air, the moisture in the air condenses and forms fog and low clouds. Also, due to the lack of air rising to higher altitudes, we see the accumulation of dust and air pollution at lower levels, and its combination with fog causes the formation of smog. All these cases reduce visibility, which is important in aviation.
- Rainfall: Temperature inversions can cause the formation of low clouds that are trapped at lower altitudes due to a lack of upward air movement. This prevents the clouds from rising to higher altitudes where they could release their moisture as precipitation. As a result, precipitation may not occur in areas affected by temperature inversions.
- Wind Shear: Temperature inversion may cause wind shear. Wind shear can be a significant hazard to aircraft, as it can cause a sudden change in wind speed and or direction horizontally or vertically at any level, so it can affect the stability and control of the aircraft. Wind shear can also cause turbulence, which can be uncomfortable for passengers and crew and can potentially causeÂ serious damage to the aircraft.
- Tornadoes and thunderstorms: Temperature inversions may cause severe thunderstorms and tornadoes due to energy trapped in the atmosphere.
- Air pollution: When a temperature inversion occurs, it can trap smoke, fog, dust, mist, and other particulate pollutants in the troposphere, reducing pilot's visibility. Also, trapped pollutants can also react with each other to form harmful chemicals such as smog. Smog is a mixture of air pollutants that can be harmful to human health if inhaled.
Effect of temperature inversion on aircraft performance
The temperature inversion is important on the performance of the aircraft during take-off and landing, and in this section we mention its most important effects.
- Reduced rate of climb and lift: In the take-off phase of the aircraft, temperature inversion reduces the rate of climb and the production of lift force by the wings, because after take-off the air becomes warmer than the surface of the earth, as a result, the density of the air decreases and this affects the performance of the aircraft.
- Increased drag: It can cause the air to be more turbulent, which can increase drag on the aircraft. This can make it more difficult for the aircraft to achieve and maintain the necessary airspeed for takeoff.
- Increased risk of wind shear: A temperature inversion can cause the wind to change direction or speed as it passes through the inversion layer. This can create wind shear, which can be a significant hazard to aircraft, as it can cause a sudden change in lift and drag.
- Increased rate of descend reduced aircraft performance: During landing, if the wind above the inversion layer is 25 knots or more and the wind below this layer is calm, it can cause the aircraft to lose its performance and lift force when passing through the inversion layer and cause the plane to sink severely.
Therefore, in order for the pilots to safely enter and pass through this layer, they must first increase the throttle and then enter this layer so that the performance of the aircraft does not decrease.
- Visibility: Usually in temperature inversions due to fog, haze and air pollution, we see reduced visibility for pilots, which can increase the risk of a missed approach or go-around.
- Glide Path: Temperature inversions can affect air density and cause the aircraft to deviate from its glide path, which may result in long or short landings.
- Turbulence: in a temperature inversion, the air close to the earth's surface is stable, which causes turbulence in the higher layers. so, the aircraft face difficult conditions during landing which is dangerous for the pilots to control the aircraft easily.
- Engine performance: Inversion can reduce the amount of oxygen available to the aircraft's engine and significantly affect engine performance and power during approach and landing. Therefore, consideration of engine power during landing in temperature inversion should be considered.Â (When there is an inversion layer, it can prevent the air from rising and mixing, which can result in a reduction of oxygen availability)