https://s3-eu-west-1.amazonaws.com/itma.dl.printmaterial/joyce_microsite/pdfs/oldirishpart2.pdf

if that link doesn't work for you try https://www.itma.ie/joyce/book/old-irish-folk-music-and-songs-part-2 and click on "view pdf"

The Winter it is Past is song #427 in "Old Irish Folk Music and Songs: The Joyce Collection Part II" (published 1909)
It was also published in Dr. George Petrie's "Ancient Music of Ireland".
Patrick Weston Joyce writes that he collected this version of The Curragh of Kildare from Kate Cudmore of Co. Limerick circa 1852.

Christy Moore has written that he found the song in the Joyce collection and that, as far as he recalls, he passed it on to Mick Maloney who was a member of The Johnstons group. So it looks like Joe Offer is probably right in surmising that Christy Moore - or one of "The Johnstons" - is responsible for adding a chorus to the song. Incidently, the next song, #428, in the Joyce Collection is "Arthur McBride".