Drizzle all over Iran (4)

I believe the answer is:

rain

I'm a little stuck... Click here to teach me more about this clue!

'drizzle' is the definition.
(I've seen this in another clue)

'all over iran' is the wordplay.
'iran' can be anagrammed to 'RAIN'.
But, I'm unsure how this is indicated.

Can you help me to learn more?

(Other definitions for rain that I've seen before include "Storm" , "Weather - shower" , "previous rule?" , "Falling moisture" , "Wet weather" .)

I've seen this clue in The Mirror.

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