Putonghua vs Standard Mandarin

Putonghua

name
  • Standard Mandarin, the official language of the People's Republic of China; the state-designated national speech of the Han nationality using Beijing pronunciation as the standard pronunciation, Beijing speech as the basic dialect, and the model writing of the modern vernacular prose as the norm for grammar. 

Standard Mandarin

noun
  • The official language of the People's Republic of China and the Republic of China, based on the Beijing dialect of Mandarin and accepted as a lingua franca for Han communities worldwide. 

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