What broke the darkness at the Siege of Minas Tirith?

[Mnemosyne]

I always thought it was the same wind from the Sea that hastened Aragorn's arrival upriver, and that later on dispelled the clouds of Mordor enough to let Sam and Frodo get their glimpse of light.

Elrond's power (which is supposed to be associated with wind) seems pretty localized. Galadriel's, too, unless you want to credit F&S's speaking in tongues to osanwe with her (which I'm not willing to do). And Gandalf is not really in the position at this point to oversee or foresee anything so far as drumming up a wind from the sea so that it'll reach the battle exactly when he confronts the WK.

I would attribute it to one of the higher Powers, as you suggest, who are rarely mentioned in LotR itself:

Originally Posted by The Land of Shadow, RotK

There was battle far above in the high spaces of the air. The billowing clouds of Mordor were being driven back, their edges tattering out as a wind out of the living world came up and swept the fumes and smokes towards the dark land of their home. Under the lifting skirts of the dreary canopy dim light leaked into Mordor like pale morning through the grimed window of a prison.

"Look at it, Mr. Frodo!" said Sam. "Look at it! The wind's changed. Something's happening. He's not having it all his own way. His darkness is breaking up out in the world there. I wish I could see what is going on!"

I think the imagery here and elsewhere suggests that something conscious is going on (i.e., it's not just coincidence), and whatever it is is much more removed from events than such figures as the bearers of the Three.

And this just became XXX-posting.