hibernal vs hyperborean

hibernal

adj
  • Of or pertaining to winter; brumal or hiemal 

hyperborean

adj
  • Pertaining to the extreme north of the earth, or (usually jocular) to a specific northern country or area. 

noun
  • Any person living in a northern country, or to the north. 

  • One of a race of people living in the extreme north, beyond the north wind. 

How often have the words hibernal and hyperborean occurred in a corpus of books? (source: Google Ngram Viewer )