That 7 second video of a small rocket shot into a cloud to induce a lightning strike (about half way down the article) is incredible.

https://www.youtube.com/watch?v=5BJIiX9_c_M

Any ideas why the lightning strike appears mostly green (and momentarily purple and orange)?

I'm imagining it's something related to the copper wire.

I always wanted to replicate this with a helium balloon and a long, wet string coated with copper filings.

You'd probably need a very large balloon to overcome the weight of the string

Maybe just salt water and skip the filings?

So, nothing new?

The cosmic ray hypothesis has been dominant for a few years now.

This magazine…

Tl;dr lightings may be caused by electrons/positrons from outer space hitting a cloud and initiating an "avalanche" of electrons.

Cosmic rays are mostly protons, not electrons or positrons. You're mixing up to separate theories in the article.

just in case you missed it, all matter carrys a charge, and all space(and matter) has energy radiating through it, making the universe an energy gradient.

sometimes you can see it happening.