CRA-LICOM: A global high-frequency atmospheric and oceanic temporal gravity field product (2002-2024)

The sub-daily high-frequency Earth gravity signal, dominated by atmospheric and oceanic mass change, is essential for understanding weather and climate change. It also serves as a fundamental data set for almost all existing terrestrial or space-borne geodetic observations, enabling the separation of desired signals. In particular, it provides unique input for satellite gravimetry such as GRACE, and GRACE-FO, to prevent the aliasing error, which is deemed the largest error source of existing missions and future next-generation gravity missions as well. Therefore, it is also called a de-aliasing product.

However, since establishing a global observation network to monitor/capture the high-frequency gravity signal is impractical, ongoing efforts are made to simulate such signals by driving the atmosphere/oceanic numerical model with a specific climate forcing field and assimilating observational data. By using the recently released CRA-40 (the 40-year global reanalysis dataset released by China Meteorological Administration) as the forcing field, we managed to drive the in-house 3-D atmospheric integration model and the LASG/IAP Climate System Ocean Model 3.0 (LICOM3.0) to reproduce a new high-frequency atmospheric and oceanic gravity de-aliasing product, called CRA-LICOM. It has a resolution of 6-hourly@50 km and covers the global domain from 2002 to 2024.

Due to the new data source and numerical models, CRA-LICOM can be deemed completely independent from the official product for GRACE, which helps in understanding the realistic uncertainty of high-frequency gravity signals. The atmospheric tidal and non-tidal components from CRA-LICOM show high consistency with the GFZ product, and ocean bottom pressure biases are minimal in most global ocean regions, with notable exceptions in the marginal seas near continental shelves. Furthermore, CRA-LICOM demonstrates a high correlation (>0.8) in Stokes coefficients with the GFZ official product until degree 20. Temporal gravity field recovery from GRACE using CRA-LICOM also aligns well with GRACE official products. Scientific applications that aim to understand the fast-changing global water cycle, as well as mission design of future satellite gravimetry that seeks accurate gravity de-aliasing, would benefit from our product. The data will be freely available at https://data.tpdc.ac.cn/.