Melody in the atmosphere (3)
I believe the answer is:
air
I believe this clue is a double definition.
'melody' is the first definition.
(air can mean a tune or melody)
'the atmosphere' is the second definition.
(synonyms)
'in' acts as a link.
(Other definitions for air that I've seen before include "character" , "Broadcast - song" , "Broadcast j" , "Gas mix surrounding the earth" , "piece of music" .)