It's currently in circulation (4)
I believe the answer is:
eddy
'circulation' is the definition.
The answer and definition can be both related to natural events as well as being singular nouns.
Maybe there's an association between them I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for eddy that I've seen before include "Swirl; Duane -, US guitarist" , "Whirling current" , "movement going round in circles" , "Water circulating" , "Swirling current" .)