August, and current's rising in force (8)
I believe the answer is:
'august' is the definition.
'current's rising in force' is the wordplay.
'current' becomes 'air' (a current of air).
'rising' is a reversal indicator (going up in a down clue).
'in' is an insertion indicator.
'force' becomes 'impel' (synonyms).
'air' in reverse letter order is 'ria'.
'ria' put within 'impel' is 'IMPERIAL'.
'and' is the link.
(Other definitions for imperial that I've seen before include "I prime Al to describe the rule of great territories" , "Majestic, like UK gallon" , "Of UK weights and measures" , "Magnificent; small pointed beard" , "Relating to empire" .)