PolyU2025 SLA: a global 0.25°  ×  0.25° monthly sea-level anomaly dataset (1993–2024) determined from satellite altimetry for sea-level and climate change research

Abstract. Long-term and spatially consistent sea-level anomaly (SLA) products derived from satellite altimetry are fundamental for sea-level and climate change studies. In this study, we develop the PolyU2025 SLA (The Hong Kong Polytechnic University 2025 sea-level anomaly), a new global monthly gridded SLA product generated using a fully independent data-processing framework. This product is provided on a regular 0.25°×0.25° grid and spans the period from January 1993 to December 2024 and is intended to be updated regularly. The PolyU2025 SLA is evaluated through systematic intercomparisons with the Copernicus Climate Change Service (C3S) gridded SLA product as well as with independent tide gauge observations. The results demonstrate a high level of consistency between PolyU2025 and C3S at global and basin scales, characterized by near-zero differences in global-mean SLA and statistically indistinguishable estimates of global mean sea-level trends and accelerations, indicating that both products are suitable for long-term sea-level change studies. At regional and short time scales, differences between the two products become more pronounced, particularly in dynamically active regions, and are mainly associated with differences in the representation of short-term and mesoscale variability. These differences reflect methodological trade-offs in data processing and spatial mapping rather than systematic biases. Overall, the PolyU2025 SLA provides a robust and consistent characterization of sea-level change from regional to global scales and serves as a complementary dataset to existing gridded SLA products, especially for long-term and climate-oriented sea-level studies and multi-product assessments of regional sea-level variability and uncertainty. The PolyU2025 SLA product is openly available at https://doi.org/10.5281/zenodo.17810525 (Yuan et al., 2025).