Hmmm...now I have really no idea what you want or don't want
Disabling terrain rendering logically removes the incoming bounced light from the terrain.So it would be better to have the terrain rendering enabled so that your tests give the results you eventually want as this is now biased.
Apart from that this looks a bit bright, may be, I don't see anything problematic.
So if you want to reduce brightness then simply decrease cloud colour a bit (0.05 - 0.1 increments).
But, again, I don't know what you want?
Can you post a version with the terrain and then point us what it is you're looking for or want to have removed?