Does a creature have to be directly in contact with the ground to be affected by the Destructive Wave spell?


My character just got the destructive wave spell, which is a great AOE for close quarters combat (you designate who it affects). However, the other spell I use for that (spirit guardians) says it affects “Self (15-foot sphere)”, while Destructive Wave says it affects “Self (30-foot radius)”. The damage type is both Thunder and Radiant, both of which might be able to travel through the air. It says the wave “ripples” away from me, but again that could be in the air. It says it can knock opponents prone, making me wonder if they have to be standing.

Does a creature have to be directly in contact with the ground to be affected by the destructive wave spell? If so, does sitting in a tree, standing on a bar/table, or in a windowsill count as being in contact with the ground (as they would hopefully transmit the wave from the ground to the target)?