openifs-radiation-torch — Bit-exact differentiable OpenIFS radiation parameterization (GMD submission version)

A bit-exact differentiable PyTorch port of the ECMWF OpenIFS 48r1 broadband radiation parameterization (6-band shortwave + RRTM-G longwave), accompanying the manuscript "A bit-exact differentiable reformulation of the OpenIFS broadband radiation parameterization" submitted to Geoscientific Model Development.This archive contains the complete source code, Fortran reference library build scripts, all experiment drivers, and all figure-generating data for the manuscript.

The reformulation achieves bit-exact agreement with the Fortran reference (max absolute difference below 1e-14 across all 12 shortwave stages) and enables automatic differentiation through the full radiation chain.Key features:- Bit-exact verification (12 stages, max |Δ| < 1e-14)- Global SW+LW sensitivity fields on ERA5 0.5° grid- Cloud radiative effect (CRE) analysis with real cloud fields- Gradient-based parameter calibration (surface albedo, cloud fraction)- All figures and scripts included for reproducibilityRelease tag: v0.1-submissionGitHub: github.com/yangjinhui11/openifs-radiation-torch