Temperature inversion or thermal inversion, as the name suggests, is the inversion or reversal of the normal tendency of temperature. This phenomenon occurs in the troposphere, the lowermost layer of the atmosphere. In normal circumstances, the temperature of the air decreases with increasing height in the troposphere. Temperature inversion happens when a layer of warm air goes above a layer of cool air within the troposphere.
Factors Affecting Temperature Inversion
1. Shape of the landscape
The shape of the landscape affects formation as well as the intensity of temperature inversion. In flat terrains, for example, temperature inversion gradually intensifies if the surface cools down. Cold air flows down the slope and settles under the layer of warm air thus intensifying temperature inversion over valleys.
2. Duration of day and night
Temperature Inversion may frequently develop during night as the amount of heat lost due to terrestrial radiation exceeds the incoming solar radiation at night. The long and cold winter nights thus are favorable for temperature inversion.
3. Amount of cloud cover
Clouds works as an obstruction for escaping terrestrial heat. So, a cloudless and clear sky intensifies the speed of loss of heat by terrestrial radiation thus favoring the occurrence of temperature inversion.
4. Humidity near the ground surface
Water vapor present in the air acts as an absorbent for the radiated terrestrial heat. Consequently, dry air near the earth’s surface limits the absorption of heat thus favoring temperature inversion.
5. Movement of air
Air works as a balancing force by transferring heat from one place to another. The slow movement of air, thus, hinders the transfer and mixing of heat at the lower level. This can result in temperature inversion at places where the surface is cool.
6. Type of surface
Different surfaces of the earth has differing albedo or reflectiveness and hence they affect the temperature differently. For example, the earth surface which is covered with snow loses maximum heat thus creating a zone of temperature inversion.
Types of Temperature Inversion
1. Frontal Temperature Inversion
The frontal temperature inversion occurs when a cold air mass undercuts a hot air mass. This is called frontal inversion because this occurs when warm and cold fronts meet. The front between the two air mass has a layer of warm air above it and a layer of cold air below it. Frontal inversion has a considerable slope whereas other types of inversions are horizontal. This inversion is very unstable and is easily destroyed by a change in the weather.
2. Vertical Advection
Vertical Advection can also be termed as valley inversion as this phenomenon is seen in intermontane valleys. As hotter air rises cold air flows down the slopes and settles beneath the layer of warm air. This type of temperature inversion is very intense in middle and higher latitudes. The regions of high mountains and deep valleys also have a strong vertical advection.
3. Radiation Inversion
Radiation inversion is also known as surface temperature inversion because it is caused due to the radiation of the earth’s surface. It mostly occurs on cold and clear nights when earth’s surface cools off rapidly due to terrestrial radiation. The air in contact with the ground cools until it gets colder than the layer of air above it thus inversing the temperature.
4. Subsidence Inversion
Subsidence temperature inversion is also known as upper surface temperature inversion as it occurs in the upper part of the atmosphere. When a mass of air descends, it gets compressed and heated due to increased atmospheric pressure. It creates a stable layer which reduces the lapse rate of temperature. This normally happens during an initial anticyclone.
Effects of Temperature Inversion
Temperature inversion is the reversal of the normal tendency of temperature to decrease with increasing altitude is a natural phenomenon. However, it can be intensified by air pollutants. Temperature inversion has some important functions like determining precipitation and formation of clouds and frosts. Furthermore, temperature inversion also has a significant impact on air quality. Here are the most common effects of temperature inversion.
- Sometimes temperature inversion occurs for a very short period. But, if the condition continues for a little longer, it traps air pollutants beneath the layer of the warm air and creates hazardous air quality near the earth’s surface. The strength, duration, and height of the thermal inversion determine the severity of pollution events, independent of the production of pollution. The longer the inversion more will be pollution built up and hence worse will be the air quality.
- Temperature inversion also affects the movement of air. It creates a stable layer thus preventing free upward and downward movements of air in the atmosphere.
- Temperature inversion hinders the upward movement of convection clouds. This means that convective clouds cannot rise high enough to produce a shower. A reduction in the amount of rain in an area can directly affect agricultural productivity.
- The layer of warm air above the layer of cold air results in the formation of fog which reduces visibility. When fog persists for a long while it causes disturbances in movement and transportation on earth. It can also become a reason for some fatal road accidents. In addition to fog, smoke and dust particles too get accumulated and restrict visibility.
- Thermal inversion, as we know, blocks normal convection patterns of an area. This releases intense energy which can cause thunderstorms and tornadoes. As temperature inversion is more intense during winter, the severity of thunderstorms and tornadoes too are higher.
- Temperature inversion reduces the diurnal variations in temperature. In other words, temperature inversion makes weather more stable and prevents large variation in minimum and maximum temperature during a day.
- The lower parts of valleys sometimes reach even below the freezing point while the air at higher altitudes remains comparatively warm due to thermal inversion. The trees and plants on the lower part of the slope thus get frostbitten due to the reversal in temperature pattern. The cap of warm air seals the cold air along with air pollutants at the base of the valley thus creating an extremely hazardous environment for the people and animals residing in intermontane valleys.
- Radio signals may be disturbed in the area with temperature inversion. This is because most of the rays would get refracted from the layer of warm air above the cold air.
- Thermal inversion can also limit the amount of sunlight reaching the earth’s surface by aiding in the formation of cumulus clouds.
- Blasting at quarries or any other type of explosions can prove to be extremely dangerous if a thermal inversion happens in that particular area. The capping effect of the thermal inversion reflects the blast waves towards the ground thus spreading the hazardous effect of blasting farther than intended. This hazardous effect can spread up to several miles away from the blast location.