Experimental atmosphere bloom is pretty nice, it doesn't really glow the clouds though, but with other things would probably help with realism. Like for city light glows talked about recently.
I wonder if you used unclamped PFs for your glow, you could clamp it in for the ground glow raising black point, and in for the clouds glow, you could use negative black values, and a smoothing function to possibly get some faked glow spread. You can always convert the PFs to grayscale, and use a constant colour with add multiplied colour, and then a multiply colour to get a more diffused constant colour.