According to the urbandictionary.com: “[t]his is a phrase used to start off your day. Similar to “good morning” but without the negative connotations. Words are vibrations that carry meaning, and “morning” sounds too similar to “mourning” while “mourning” has a negative connotation, rising instead has a positive one. You are rising from bed, the sun is rising in the sky. There is no sadness/mourning involved, we are instead grateful for another day.”
A mug is available at the Urban Dictionary Store. Really.
I first heard “grand rising” from someone from the Caribbean. It is also a reminder to rise up against oppression.
It is a spiritual affirmation.
And the response to “grand rising”? of course, saying it back and then whatever you used to say after “good morning”.
And so it is.