URUANA DE MINAS — EMM2017 HIGH-DEGREE RESOLUTION-LADDER AUDIT

Uploaded package: EMM2017 spherical-harmonic Linux package.
Implementation validation:
- The bundled NOAA/NCEI GeomagnetismLibrary.c was compiled locally.
- Full EMM2017 at the official test coordinate (2017.0, lat 0°, lon 123.7°, ellipsoid height 0 km) reproduces the package test values:
  X = 39126.87 nT, Y = 399.49 nT, Z = -11120.06 nT, H = 39128.91 nT, F = 40678.34 nT.
This validates the evaluator against the archive's own reference output.

MODEL SPLIT
- Degrees 16-133: retained as a coarse static crustal block.
- Degrees 16-790: retained as the full static crustal block.
- Degrees 134-790: isolated exactly by linear subtraction / coefficient masking.
- No 2017 core field or secular variation is used from EMM in the 2026 sensitivity hybrid.
- Sensitivity hybrid = official WMMHR-2025 field evaluated for 2026.61644 + static EMM2017 degrees 134-790.
This hybrid is NOT an official NOAA 2026 model. It is a controlled scale-addition experiment.

PRIMARY FROZEN CORRIDOR
Center = -16.0593, -46.2585
N-S fit = -8 to +8 km about the city.

SCALAR TOTAL-FIELD GRADIENT
WMM main:                         +1.141745 nT/km
WMMHR:                            +1.321468 nT/km
WMMHR + EMM(134-790) hybrid:      +0.808092 nT/km

Coarse WMMHR-WMM F increment:     +0.179723 nT/km
Finer hybrid-WMM F increment:     -0.333653 nT/km

KEY RESULT
The sign of the modeled crustal contribution to the scalar F gradient changes with added smaller-scale content:
coarse WMMHR increment = positive;
after adding degrees 134-790 = negative.
The total field itself remains positive northward, so this is NOT a complete 2026 modeled total-field inversion.

The finer hybrid suppresses the WMM main-field gradient by 29.2%.
Descriptive competition ratio |G_crust|/G_main = 0.292 (<1), so the modeled fine-scale crustal opposition is not large enough to reverse total F at this model scale.

VECTOR GRADIENTS
WMM:       (+3.267230, -1.274038, +3.298705) nT/km
WMMHR:     (+3.172795, -1.501568, +2.970453) nT/km
Hybrid:    (+2.764817, -1.003285, +3.043463) nT/km

WMMHR-WMM increment:
(-0.094434, -0.227530, -0.328252) nT/km

Added EMM degrees 134-790:
(-0.407978, +0.498284, +0.073010) nT/km

Hybrid-WMM total increment:
(-0.502412, +0.270754, -0.255242) nT/km

INCLINATION-GRADIENT RESULT
WMMHR-WMM:                  -2.354 arcsec/km
Added degrees 134-790:      -2.188 arcsec/km
Hybrid-WMM total:           -4.542 arcsec/km

Thus the signed inclination-gradient perturbation keeps the SAME upward-directional sense and approximately doubles in magnitude when the smaller-scale degrees are added.

GRADIENT ROTATION / RADIAL-TANGENTIAL
Angle WMM -> WMMHR gradient: 4.249 deg
Angle WMMHR -> hybrid gradient: 6.952 deg
Angle WMM -> hybrid gradient: 2.897 deg

Coarse increment tangential-energy fraction: 81.0%
Added high-degree increment tangential-energy fraction: 36.6%
Hybrid-WMM total tangential-energy fraction: 70.9%

LONGITUDE ROBUSTNESS
Across the four supported N-S tracks from ~20 km west to ~10 km east:
- hybrid-minus-WMM F-gradient is negative in 4/4 tracks;
- hybrid-minus-WMM inclination-gradient is negative in 4/4 tracks.
This means the scale-emergent opposition is not restricted to the exact city longitude.

IMPORTANT HISTORICAL CONCORDANCE
At the central track the fine-scale hybrid crustal F-gradient is -0.334 nT/km.
The independently reconstructed 1971-72 CGBA residual had previously been estimated at about -0.356 to -0.233 nT/km.
The numerical overlap is striking, but it must NOT be counted as independent replication because EMM/EMAG2 can inherit legacy aeromagnetic compilations.

VERDICT
PASS for resolution-emergent crustal opposition:
Adding degrees 134-790 changes the modeled crustal scalar-gradient contribution from reinforcing the main field to opposing it, while strengthening the signed inclination-gradient perturbation in the same direction already seen in WMMHR-vs-WMM.

FAIL for a complete modeled 2026 total-field inversion:
the hybrid total F gradient remains positive.

STATUS
Corroborative/model-sensitivity evidence only. The direct proof of local scalar-gradient inversion remains the 2011 raw same-line result. Direct local vector-Z/inclination proof remains reserved for measured fX/fY/fZ.