Frost Atronachs have "AbAtronachFrostEffect "Atronach Frost" [SPEL:0008DAA6]" made for them, but it isn't assigned. I thought maybe this was cut content, but Storm and Flame atronachs have their effects assigned and UOP also assigns Frost Damage the correct frost sound effects, so I am still reporting this just in case.
If this is a bug, then the effect should be added to: 0001ff22, 0007be5c, 0007be5d, 0007be5e, 0007be64, 000c8bca, and 01003435 (added by UOP).
There is also a Test Frost Atronach, but this one probably only appears in test cells, so that one can be ignored.