What exactly is the white we see coming off an airplane in the sky. Sometimes in the summer you can lookup and see many streaks in the sky. They are much longer and last longer in the summer than winter. Please tell me what causes this and why they last longer in the summer.

The white streaks you see coming off airplanes are called contrails. That is short for condensation trail. Contrails are actually clouds made by the airplanes.

An airplane's exhaust has some water vapor in it, just like the air. Sometimes when the exhaust mixes with the air, it has so much water vapor that the air can't hold it all. The water vapor then turns into clouds. That's why you sometimes see contrails following jet airplanes.

The air has more water vapor in it during the summer. That means that it's more humid than during the winter. Contrails will last longer during the summer because the clouds won't evaporate very fast in the humid air.

What exactly is the white we see coming off an airplane in the sky. Sometimes in the summer you can lookup and see many streaks in the sky. They are much longer and last longer in the summer than winter. Please tell me what causes this and why they last longer in the summer.

The white streaks you see coming off airplanes are called contrails, which is short for condensation trail. Contrails are actually clouds made by the airplanes. There are two types of contrails.

Most contrails people see are caused by a jet's exhaust. The exhaust has some water vapor in it which mixes with the air when it leaves the jet's engine. Sometimes this mixture has too much water vapor for the air to hold and it condenses into a cloud. This is the most common kind of contrail and it lasts the longest.

The other kind of contrails are form by an airplane's wing. Air moves over the wings really fast and cools because of the low pressure. The cool air can't hold as much water so some of it has to condense. This kind of contrail isn't as long-lived as the other kind. The picture to the left is an example of this kind of contrail.

Contrails last longer when there is a greater amount of water in the air. During the summer, the air generally has more water vapor in it than during the winter. You might notice that it's usually more humid in the summer. Because it's more humid in the summer, contrails take longer to evaporate. That's why they last longer than in the winter.

What exactly is the white we see coming off an airplane in the sky. Sometimes in the summer you can lookup and see many streaks in the sky. They are much longer and last longer in the summer than winter. Please tell me what causes this and why they last longer in the summer.

The white streaks coming off jet aircraft are called contrails, which is short for condensation trail. Contrails are similar to clouds and are created by the aircraft. Contrails are formed two different ways.

The most common type of contrail is caused by a jet's exhaust. The exhaust adds water vapor to the air and may cause the air to become super-saturated. Because there is so much water some of it can condense and form the cloud you can see from the ground.

The other type of contrail is called an "aerodynamic contrail" and is caused by an aircraft's wings instead of its engine. When the air moves past a wing it creates a low pressure area (which is how planes fly). The lower pressure causes the air to cool and possibly reach saturation. This type of contrail (seen in the picture) doesn't last very long; it gets disrupted by the aircraft's wake.

Exhaust contrails are the ones you can see from the ground. They will last until the water in the clouds evaporates. During the summer the air is usually more humid than in winter. This means that evaporation will be slower and contrails will last longer.

Last modified prior to September, 2000 by the Windows Team

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