There are times when Japanese pronunciation really leaves me scratching my head. For example, the word 上半 is pronounced as じょうはん, and 上半身 is pronounced as じょうはんしん. So when I first saw the word 上半期, I thought it would be pronounced as じょうはんき. However when I looked up the dictionary, I found that the pronunciation is actually かみはんき. (Similarly, 下半期 is pronounced as しもはんき rather than かはんき.) Can someone please explain to me why the two different pronunciations for 上半. For example, how should 上半年, 上半月 and 上半部 be pronounced? Thanks!