This 嗚呼. I don't know if you ever seen it – combination of weep and call. It has an exceptional reading ああ. And the meaning is: well, there is no meaning. Literally meaningless. It is 'aa' you sometimes put into song lyrics, when you want to sing 'aa' in order keep rhythm, or just make the song pretty. (I am no language expert, maybe in other context it actually has some meaning, but in those songs i have seen it, it works like this).
Yes, (some?) Japanese decided to make singing "aa" a word worth encrypting with Kanji. Nothing will surprise me anymore.
by Player_One_1