The PM arose to change prevailing mood (10)

I believe the answer is:

atmosphere

'prevailing mood' is the definition.
(atmosphere can mean a mood or air)

'the pm arose to change' is the wordplay.
'to change' is an anagram indicator.
'the'+'pm'+'arose'='thepmarose'
'thepmarose' anagrammed gives 'ATMOSPHERE'.

(Other definitions for atmosphere that I've seen before include "Pervading tone or mood" , "Gas surrounding a planet" , "prevailing mood" , "blue?" , "character" .)

I've seen this clue in The Independent and The Times.

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