Well. People will probably ask how i managed to get this effect. The honest answer is i haven't got a clue. Most of the settings, especially the cloud settings are standard. I think i just got really lucky with the placing of the clouds in this piece which gives it the huge difference between the left and right side. There certainly doesn't seem to be anything else which could explain it.
I just mucked about with the atmosphere a wee bit then did some postwork on the colours in photoshop. I'm in two minds as to whether the original colours are actually better than the version that you can all see here.
I had massive problems rendering it in this size ration of 1:1.5. It wouldn't do a 3000 x 4500 render without leaving chunks missing at the top or bottom. I even tried the 180 degree bank technique to fill in the blanks but that didn't help. I ended up rendering it at 2000 x 3000 instead, even though i had spent about 32 hours in failed renders before that.
Anyway, i hope you enjoy.
[EDIT] added the world and terrain files for people to peruse and dissect.