What Are Contrails, Types, Formation, And Advantages?

The white color smoke line that is made by an aircraft during flying is known as a contrail or condensation trail. Aviation plays a significant role in global climate change, extending beyond carbon dioxide emissions. The operations of aircraft directly influence the climate through the formation of contrails, which are linear cloud formations visible behind aircraft on clear days. These contrails affect the absorption and reflection of solar radiation, thus impacting planet warming and cooling. 

Definition

The white elongated turbulence-shaped clouds formed on the path of the aircraft. It is mostly formed on the upper troposphere layer but can also be formed on the ground or any level depending on the temperature, humidity, and aircraft type.

Factors for the formation of Contrails

Contrails are formed when warm engine exhaust, containing water vapor and particles, is released into the cold ambient atmosphere. The vapour condenses into water droplets on the particles, which freeze if the temperature is sufficiently low. Contrails can evaporate within minutes or persist for hours, spreading to form cirrus clouds.

Two factors that determine the formation of contrails

1. Environmental factor
2. Aircraft parameter
3. Atmospheric Conditions
4. Atmospheric Dynamics
5. Fuel Composition

Environmental factors include

1. Pressure
2. Temperature
3. Humidity

Aircraft parameters

The aircraft’s wingspan, size, and propulsive efficiency contribute to the contrails’ characteristics. It is the ratio of water vapours to the heat injected into the wake for the jet aircraft; as compared with prop aircraft, almost the entire heat and water vapours are liberated while combustion goes into the wake.

Fuel Composition

The type and blend of fuel used to power jet engines impact contrail formation and properties.

Type of Contrails

Exhaust Trails

As we see also when we ignite the engine of a car or motorcycle, the water droplet will come out from the exhaust because fuel contains water particles, and the fuel contents are burned, and the water will come out from the exhaust. As far aircraft, the exhaust will increase the humidity of the air, and if the moisture level is high, the trail will remain for a longer time, even converted into clouds. This type of layer occurs when the air temperature falls below the critical level, 25 degrees C from sea level to -45 degrees C at 50 000.

Mintra level (Minimum trails): The critical temperature, which is only slightly affected by the type of aircraft, is known as Mintra temperature and applies to an aircraft rate with to ice is known as Mintra level. The contrail is expected to be formed above the Mintra level.

Aerodynamic Trails (wing-tip)

Aerodynamics forms these trails due to the reduction of pressure at the wing tips of an aircraft. The temperature decreases up to the dew point due to expansion. Such trails are seen during the mild damp weather at low altitudes. This effect also occurs on the blades of the propeller, i.e., wind tips and over the wing’s surface.

Operational advantages of Contrail

Radiative Effects of Contrails

During the day, contrails and cirrus clouds lead to shortwave solar radiation reflection back into space. While contrails reflect incoming solar radiation, cooling the atmosphere they also stop the outgoing long waves that end up warming the atmosphere. The net radiative impact of contrails is measured in terms of the radiative forcing metric.

• Contrails are very helpful for detecting aircraft, so; it gives an advantage to the defender to easily spot it and trace the attacker aircraft.
• By counting the contrail lines, the aircraft type could be determined.
• The contrail can form cirrus clouds that can hinder the visual contact for the operation.
• Because of all these, the military aircraft avoid going above the Mintra level; otherwise, they won’t be able to surprise the enemy.

Dissipation of the Contrails

suppose the contrail is formed in an environment where the air is near saturation. In that case, the contrail will remain for a longer period, even converted into cirrus clouds. But if the humidity level is low, then the period of contrail won’t be long enough. The exhaust trail is uncommon here in the stratosphere because of the low humidity. 

Conclusion

Contrails’ impact on climate change is a complex topic influenced by various factors. While contrails reflect incoming solar radiation, cooling the atmosphere they also stop the outgoing long waves that end up warming the atmosphere. Estimating radiative forcing caused by contrails is challenging due to the uncertainty involved. Further research and understanding of contrail formation and behavior are essential for developing effective strategies to mitigate aviation’s contribution to climate change.