Hi guys, I am trying to imitate an aurora glow for 2d games.

I don't know if this is the right name, but it is used everywhere in Blizzard's Hearthstone card game

even on its homepage http://us.battle.net/hearthstone/en/, you can find 3 kind of aurora effect on its main banner

the banner is a movie file http://media.blizzard.com/hearthstone/videos/home-header-bg-video.webm, so its impossible to diagnose it

Here are some static screenshot

[attachment=19824:20130821031822a0dk4p1d7ree6n2m.jpg]

[attachment=19825:hearthstone-crafting-disenchant-alert-4-first-disenchant-earns-95-dust (1).jpg]

[attachment=19826:hsnewyear.jpg]

I've tried to do this with particle system, however, not satisfied with the result, and it is expensive too

[attachment=19823:auroraparticle.jpg]

any direction on how to generate this effect in real time?