ahem vs clear one's throat

ahem

verb
  • To cough or clear one's throat so as to draw attention. 

intj
  • an exclamation or cough to get attention 

  • the sound of a quiet cough or of clearing one's throat 

  • an exclamation of disapproval or annoyance 

  • an exclamation to indicate sarcasm 

clear one's throat

verb
  • Forcibly, sometimes mutedly, expelling air from one's lungs, sometimes to clear mucus, sometimes to attract attention to something; less vigorous than coughing. 

How often have the words ahem and clear one's throat occurred in a corpus of books? (source: Google Ngram Viewer )