A decade of temporal gravity observed by the ESA Swarm satellites

The ESA Swarm constellation’s dual‑frequency GPS observations provide high-low satellite‑to‑satellite tracking (hl‑SST) with sufficient fidelity to estimate monthly global gravity field variations at low degree and order (spatial half‑wavelength ≳1,500 km; SH degree ≈12–13). Since late 2013, these solutions have formed an uninterrupted time series that bridges the gap between GRACE and GRACE-FO, complementing the short interruptions in their records. Independent gravity inversions - Celestial Mechanics, Decorrelated Acceleration Approach, Short‑Arcs, and Improved Energy‑Balance - are generated by a consortium comprising AIUB (Switzerland), ASU (Czechia), TU Delft (the Netherlands), TU Graz (Austria), and Ohio State University (USA). The solutions are combined at the level of normal equations using Variance Component Estimation (COST‑G), yielding consolidated monthly products that are largely unbiased with respect to any single strategy.We publish the models quarterly via ESA’s Swarm Data Access and ICGEM, ensuring traceable, community-ready datasets for geophysical applications. Cross-validation against GRACE/GRACE‑FO demonstrates that Swarm recovers large-scale hydrological and cryospheric mass changes, with typical basin-scale agreement characterised by temporal correlations around ~0.75 and trend consistency within ~1 cm/yr in Equivalent Water Height (EWH). Advances in kinematic orbits processing since early 2020 have tightened the nominal EWH accuracy from ~4 cm to ~3 cm. A persistent feature of the Swarm-derived fields is elevated noise over deep-ocean regions, which is 30–50% larger than over land.These hl-SST models are estimated independently of ll-SST data, enabling the validation of those gravity field solutions, providing continuity during past and prospective gaps (including the GRACE-FO to GRACE-C/MAGIC transition), and supporting low-latency monitoring of large-scale mass transport. The robust Swarm platform’s health and refined GPS processing during periods of heightened solar activity ensure the sustained delivery of high-quality monthly time-variable gravity fields.