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

The PolyU2025 Sea Level Anomaly (PolyU2025 SLA) dataset is a global monthly gridded sea level anomaly product developed at The Hong Kong Polytechnic University (PolyU). This product spans the period from January 1993 to December 2024 and is intended to be updated regularly. By providing monthly SLA fields on a 0.25° × 0.25° global grid, PolyU2025 SLA constitutes a long-term and internally consistent observational resource for studies of climate variability and sea-level change. To ensure temporal stability and adequate spatial sampling, PolyU2025 SLA is constructed using a consistent two-satellite combined constellation strategy, with a minimum of two concurrent altimetry missions adopted for each month. At each monthly time step, one primary reference mission—TOPEX/Poseidon, the Jason series (Jason-1/2/3), or Sentinel-6A—serves as the backbone of the record, ensuring long-term temporal continuity. In parallel, a second mission, which varies over time (CryoSat-2, SARAL/AltiKa, ERS-1/2, Envisat, or Sentinel-3A), is incorporated to enhance spatial coverage, improve the representation of mesoscale sea-level variability, and extend observations into high-latitude regions. This constellation design enables PolyU2025 SLA to capture sea-level variability from global to regional scales with improved spatial detail while preserving the temporal stability required for multi-decadal climate analysis. The PolyU2025 SLA product is distributed as annual NetCDF files following the standardized naming convention "dt_global_L4_yYYYY_m01–m12.nc (e.g., dt_global_L4_y1993_m01–m12.nc)". Each annual file contains three core variables: monthly SLA fields for January to December (months 1–12) of the corresponding year, longitude, and latitude, all defined on a consistent global grid to facilitate seamless analysis across the full 32-year record from January 1993 to December 2024. To facilitate temporal visualization, an animation file (dt_global_L4_y1993–2024_m01–12.gif) is provided, illustrating monthly global SLA variability throughout the 32-year record. The animation reveals spatially coherent features and temporal fluctuations linked to major climate variability and long-term oceanographic processes. Acknowledgements: This work was supported by the National Natural Science Foundation of China (grant no. 42394132 and 42394131), Hong Kong RGC Collaborative Research Fund (C5013-23G), and the Otto Poon Climate-Resilient Infrastructure Research Scheme (Project ID: ZH8Y) and State Key Laboratory of Climate Resilience for Coastal Cities at The Hong Kong Polytechnic University.