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What are those long white "clouds" you see in the sky?
If you have ever looked up and noticed a long white line stretching across the sky, you may have wondered what exactly you were seeing.
The strange-looking trails have sparked plenty of questions, with some Malaysians wondering if they are linked to rain seeding, pesticides being released into the atmosphere, or exhaust fumes coming from aircraft passing overhead.
The answer is much less mysterious: They are usually contrails, short for "condensation trails", which are clouds formed behind aircraft.
These "clouds" are actually made from water vapour
When a plane flies at high altitude, its engines release hot exhaust gases that contain water vapour.
At cruising altitudes, the surrounding air is extremely cold. When the warm water vapour from the aircraft meets this cold air, it condenses and freezes into tiny ice crystals, creating the white streaks we see behind planes.
In other words, the line is not smoke from the aircraft. It is a type of cloud made up mostly of ice crystals.
Why do some lines disappear quickly while others stay for hours?
You may notice that some aircraft trails vanish within minutes, while others remain in the sky and slowly spread out.
This depends on the conditions in the upper atmosphere.
When the air is dry, the ice crystals quickly turn back into water vapour and disappear. But when the air is cold and humid, the crystals can remain for longer and expand, sometimes becoming thin cloud layers.
Are they caused by rain seeding?
Rain seeding, also known as cloud seeding, has been mentioned whenever unusual patterns appear in the sky, especially during periods of heavy rain or haze in Malaysia.
However, normal aircraft contrails are not the same as cloud seeding.
Cloud seeding is a weather modification technique that involves introducing substances such as silver iodide or salt particles into suitable clouds to encourage rainfall. It requires specific weather conditions and is usually carried out using specially equipped aircraft.
The white lines commonly seen behind passenger planes are simply a result of normal flight.
