Comprehensive analysis of 83k records across 11 model types.
Key finding: physical variables (lat, day_of_year) explain the correct
seasonal-latitude interaction pattern, but the heterogeneous dataset has
a 3.3 degree noise floor from incompatible measurement methodologies.
Recommended DPC formula (Medium-9):
f(abs_lat, day_of_year) -> angle
9 terms: intercept + abs_lat + 4 seasonal harmonics + 4 lat*season interactions
Mandatory args: abs(latitude), day_of_year
Optional: elevation_m (+0.0007 deg/m)
Not needed: longitude (data artifact, not physics)
See analysis_results.md for full formulas with coefficients.
