Possible Incorrect Rejection of OFFLINE_CHILD_MP_PHYSICS from GPUWM Offline Downscale

[yongsua1989]

Environment
gpuwm: 2.5.2
Source: editable checkout
Python: 3.12
WRF parent domain: 9 km
Child domain: 3 km
Downscale ratio: 3
Parent microphysics: mp_physics = 6 (WSM6)

The parent namelist contains:

mp_physics = 6

The source defines:

OFFLINE_CHILD_MP_PHYSICS = frozenset({6, 8, 10, 18, 28})

and:

if source_mp_physics not in OFFLINE_CHILD_MP_PHYSICS:
    raise OfflineChildContractError(
        f"unsupported parent mp_physics={source_mp_physics}"
    )

However, _transported_source_fields(6) Line 1236 still reaches:

elif source_mp != 0:
    raise OfflineChildContractError(
        f"unsupported parent mp_physics={source_mp}")

because the function does not include 6 in its explicit field mapping.

I am unsure if this is intentional or bug, but anyway changing the code to:

elif source_mp not in {0, 6, 8, 10, 18, 28}:
    raise OfflineChildContractError(
        f"unsupported parent mp_physics={source_mp}")

removes the restriction or error for me.

Thank You.

[FahrenheitResearch]

Confirmed, and thank you for the precise report, this is a bug. OFFLINE_CHILD_MP_PHYSICS admits mp=6 but _transported_source_fields never terminates its chain for it, so WSM6 falls into the catch-all refusal. Your change produces the correct transported set for WSM6 (single-moment: qv/qc/qr/qi/qs/qg, no number fields). The fix plus a regression test that forces the declared set and the transport mapping to agree will be in the next release.