Thanks! .. this challenge is a real challenge to me because I haven't been making skies with Bryce for ages, I really prefer to paint my own skies and import the image in bryce.

Actually I'm working on an other sky image, much better than this one (IMO) using volumetric mats with lights inside... big big render time. This image could be named "night flight over storm". I hope to upload it soon.

Cheers!