Contrails

Patterns in the sky - living between several busy airports, you get to see a lot of contrails. They don't occur right near airports, because the planes have to be high enough to hit cold air.

These contrails are over Florida -

Rainbow contrails (new to me!) -

Admittedly, that's an extreme example, with conditions just right - see more here. The rainbow effect comes from the different optical properties of different sized ice crystals. They are more common with warmer weather and moister air.

A moist environment makes contrails longer-lived (pic from here), and as the wind blows them along they spread out -

Condensation trails first began to appear in skies over Britain in 1940, says this site, and became part of Paul Nash's image of the Battle of Britain -

While researching contrails, I came across some videos of flight patterns, compiled from airline data. These have fascinated me since seeing one in a "digital futures" exhibition at the V&A a couple of years ago. (So many planes in the air at one time - one estimate is a million people on planes at any time, but I don't know where I heard that...)

The most dramatic is the shutdown of US airspace on 9/11, which you can see here  - and the air traffic patterns over Europe during the Iceland volcano eruption are dramatic too - see them here (is the swelling music Tchaikovsky?).

What is worrying is the effect of aviation on climate change - currently jet planes are responsible for 5% of CO2 emissions, and this amount is set to increase. Contrail clouds trap the planet's heat. "Further research is needed..."

Finally, skywriting - call me cynical, but it all looks photoshopped these days...

...though "sky writer trailed by sky editor" (from here) did make me laugh (ruefully) ...