Temporal denoising of GRACE Level-2 Greenland mass anomalies

Monthly satellite-gravity records provide an observational measure of Greenland ice-sheet mass change but exhibit 9 degree-dependent correlated errors. This study assesses first-order Tikhonov regularization of regional equivalent 10 water height (EWH) reconstructed from GRACE Level-2 spherical harmonics truncated at degrees 60 and 96 over 11 2003–2016. Three regularization-parameter strategies—generalized cross-validation (GCV), L-curve analysis, and 12 variance-component estimation (VCE)—are examined, together with a covariance-aware adaptive first-difference 13 formulation. The EWH estimates are evaluated against GSFC mascon observations using RMSE, normalized 14 RMSE, coefficients of determination, Nash–Sutcliffe efficiency, percentage bias, temporal cross-validation, and 15 retention of the seasonal and long-term components. GCV reduces RMSE from 0.45 to 0.08 m (degree 60) and 16 from 1.20 to 0.25 m (degree 96), corresponding to reductions of 82.2% and 79.2%. The L-curve solutions yield 17 RMSE values of 0.05 and 0.18 m, respectively. The GCV solutions attain R2 values of 0.97 and 0.93, while 99% 18 and 98% of the respective long-term trend components are retained. These findings indicate that regularization 19 improves agreement with regional mascon mass anomalies while preserving major geophysical variability; 20 performance remains sensitive to harmonic truncation and parameter choice. 21