You've probably wondered about it before, what are those white streaks left behind by airplanes? How do these airplane contrails form, and why can you sometimes not see them? Let me explain.
Interaction between airplane and atmosphere
Airplanes run on kerosene. Keep in mind that airplanes typically carry between 30.000 and 100.000 liters. When one liter of kerosene is burned, about 2.5 kilograms of CO2 and 1 kilogram of water vapor are produced.
The aircraft no longer needs these substances and releases them into the air. An airplane flying at cruising altitude is at a height of approximately 11 kilometers. At this altitude, the temperature is extremely cold, around -50 degrees Celsius.
When the emitted substances from the hot engine come into contact with the freezing environment outside the airplane, they condense and freeze. The thick white lines behind the airplane are nothing more than ice crystals formed by the emitted substances.
Why can you sometimes not see airplane contrails?
The formed airplane contrails are not always visible. This depends on various factors:
- Altitude: Airplane contrails form where the air is very cold, typically above 25,000 feet (or 7,500 meters). There, in that environment, the substances can quickly freeze and disperse.
- Humidity: The stretched cloud-shaped appearance forms more easily in humid air. On dry days, the formed water vapor may condense less rapidly and freeze less quickly.
- Aircraft type: Not all airplanes produce the same amount of contrails. Newer airplanes with more efficient engines and lower emissions tend to leave less noticeable contrails.
- Atmospheric conditions: If you are flying close to or through existing clouds, the air in that location is already saturated with ice crystals, making it difficult to distinguish the formed airplane contrails with the existing clouds.
Predicting the weather
So, airplane contrails are artificially formed clouds. They often disappear immediately, but sometimes they stick around for hours. But did you know that these contrails can help predicting the weather? How does that work?
- No contrail formation: This means that the atmosphere is too dry and warm to form contrails. This is usually an indication of prospective nice, calm weather. However, it could also mean that the airplane is flying below 25,000 feet. Predicting the weather without contrail formation is the most challenging cause the factors mentioned in the previous paragraph also play a role.
- Short contrail formation: During such times, the atmosphere contains some moisture, but not much. This can be an indication of fairly to very good weather.
- Long contrail formation: The upper atmosphere is very humid, which could mean changing weather is approaching. A sky full of airplane contrails can signify that the good weather is coming to an end.
Are airplane contrails harmful?
While airplane contrails are visually striking in the sky, they are generally not directly harmful. The formed contrails consist of minimal amounts of greenhouse gases that contribute to climate change.
Although they are primarily composed of water vapor, efforts are underway to develop more efficient engines and alternative fuels to reduce the environmental impact.
Conclusion
In short, remember that airplane contrails are born from condensation and freezing of water vapor and exhaust gases. They often disappear immediately, but sometimes they stick around for hours. Will you be able to predict the weather next time based on airplane contrails?
Good luck!
By: Rico Valkenborgh | November 8, 2023
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