graupel vs hailstone

graupel

noun
  • A precipitation that forms when supercooled droplets of water condense on a snowflake. 

  • The result of this process, a small ball of rime. 

hailstone

noun
  • A single ball of hail, or solid precipitation 

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