Both examples come from a contraction of two words into one evolving from Middle High German:

draußen - mhd. dār ūʒen^Duden

or, in your other example from

droben - dort oben^Duden

Both examples come from a contraction of two words into one evolving from Middle High German:

draußen - mhd. dār ūʒen^Duden

or, in your other example from

droben - dort oben^Duden

Examples where both variants coexist are

dran - daran, drüber - darüber, drum - darum, drauf - darauf [...]