Bc the ground is ~the same temp all year so there are no seasons down there just consistency.
Your ground water remains constant, as in a pump and dump. A closed loop does not remain constant. To answer the original question.... I ave had it explained to me a half dozen times and it allways involves a equation for conversion. Way above my pay grade.
Think of it this way on a heat pump COP is how efficient it is at a given temperature(47degrees for air source) and HSPF is the seasonal average. So if a system has an HSPF of 9 divide by 3.413 and it has an average COP of 2.63
SEER and EER are a but more difficult. EER is still an efficiency at a given temperature if I remember correctly its about 82 degrees outdoor with 78 indoor temps and 1 EER means 1 watt of energy removes 1 BTU of heat.
So back to your question, air source could have the same EER but with geo systems rated up to 41 EER and air source having up to 14 or 15 EER there is a long way to go.
It's actually a complicated issue since any heat pump, water or air source loses capacity and efficiency as the temperature drops or flow is reduced on the source cooling fluid...whether air or water.
If we're talking dual fuel for example, a air source heat pump above 45F can have COP's up around 4.... not far from geothermal. Similarly, EER at 60F on a higher effciency air soruce unit can approach 20.
So it's one of those "it depends" answers. The more research I do, the more I realize that delivered efficincy on both system can vary widely. That's why a good installer is so, so improtant, and absolutely critical on geothermal.
A EER or 41 is a COP of 12. That's just crazy. Non inverter water ot water cna get pretty high too under the right conditions.