Striking atmospheric phenomena (13)
I believe the answer is:
thunderstorms
'striking atmospheric phenomena' is the definition.
'thunderstorms' can be an answer for 'phenomena' (thunderstorm is a kind of phenomenon). I am not sure about the 'striking atmospheric' bit.
'atmospheric phenomena' is the wordplay.
'atmospheric' becomes 'thunder' (I can't justify this - if you can you should give a lot more credence to this answer).
'phenomena' becomes 'storms' (storm is a kind of phenomenon).
'thunder'+'storms'='THUNDERSTORMS'
(Another definition for thunderstorms that I've seen is " weather".)