Sine wave in the sky over Singapore
[23 Feb 2008]
I had a friend who was heavily into gliding. He would become very excited when he observed “wave” in the sky.
Gliders (aka sailplanes) don’t have engines, of course, so you spend all your time looking for lift.
The lift comes from thermals (rising hot air, usually over dark-colored ground) or waves that are the result of wind blowing over mountains. When airflow is lifted by a mountain range, it is called ‘orographic uplift’.
[Image source, from Natural History of the White-Inyo Range, Eastern California.]
So in gliding, “wave” is a standing sine curve on the leeward side of a mountain.
I saw the following wave pattern over Singapore recently. The clouds are much higher than where gliders can reach, but there is evidence of alternating rise and fall of the moist airmass. In this case, the wave could be the result of air passing over mountains in Indonesia (there are no mountains in Singapore).