Unveiling North–South stripe patterns in the GRACE gravity field using dimensionality reduction

SUMMARY The spherical harmonic coefficient Level-2 products of the Gravity Recovery and Climate Experiment (GRACE) mission are affected by north–south stripe noise. Toward this end, we proposed a new filter named Variational Mode Decomposition spatial (VMDS) filter that transforms an equivalent water height (EWH) map derived from GRACE Level-2 product into a 1-D sequence, which is then filtered by using variational mode decomposition. This approach overcomes the limitations of the singular spectrum analysis spatial (SSAS) filter, which performs well in the medium-frequency band but omits the high-frequency NSS noise. Integrating the strengths of both, we developed a combined filter termed SV by placing the VMDS filter behind the SSAS filter. A closed-loop simulation demonstrates the better ability of SV to suppress NSS noise and preserve signal at the grid scale compared to the SSAS filter. In the real-world scenario, the SV solution achieves a noise level (46.68 mm of EWH) below that for SSAS and DDK7 solutions (53.52 and 53.68 mm of EWH, respectively) over the ocean at low latitudes. Moreover, the well-documented water level of Lake Victoria and the well-modelled coseismic gravity change of the Mw9.2 2004 Sumatra-Andaman earthquake demonstrate that the SV filter efficiently preserves localized mass evolutions while suppressing north–south stripe noise. Such short-wavelength signals are usually missed in highly filtered spherical harmonics (e.g. DDK5 and DDK6) solutions or are significantly inconsistent for various mass concentration solutions.