Temperature in the atmosphere (4)
I believe the answer is:
heat
'temperature' is the definition.
(heat is a kind of temperature)
'in the atmosphere' is the wordplay.
'in' says the answer is hidden in the clue.
'HEAT' is hidden in the letters of 'the atmosphere'.
(Other definitions for heat that I've seen before include "Get agitated" , "Warmth - passion" , "Provide warmth" , "early round" , "Preliminary race to qualify finalists" .)