Rule 5b. Never use single quotation marks in sentences like the previous three. Incorrect: I had a visit from my 'friend' the tax man. The single quotation marks in the above sentence are intended to send a message to the reader that friend is being used in a special way: in this case, sarcastically. Avoid this invalid usage.
Why do jets leave a white trail in the sky? Jets leave white trails, or contrails, in their wakes for the same reason you can sometimes see your breath. The hot, humid exhaust from jet engines mixes with the atmosphere, which at high altitude is of much lower vapor pressure and temperature than the exhaust gas.
Jet streams do not usually move in straight paths; the path of a jet stream typically has a meandering shape. Each large curve or meander of the jet stream is known as a Rossby wave. Jet streams follow the boundaries between hot and cold air. Since the temperature changes in the atmosphere are greatest around 30Â° and around 50Â°â60Â° in the Northern and Southern Hemispheres, this is where the jet streams form.