Yonghong Zhou

With the increasing demands for global development, deep space exploration missions are taking place more frequently, rendering the traditional 24‐hr Polar Motion (PM) predictions inadequate for supporting the frequent operations of spacecraft. Therefore, this study utilized the mainstream EOP C04 and EOP C04 spliced with the final.daily series to evaluate the performance of interpolating PM to 6‐hr and then forecasting, under both ideal and real‐world environments. Interpolation is performed using the Stable Ultra‐high‐Precision‐Radial‐Basis‐Function (SURBF) and the Seasonal‐Trend‐Residual decomposition with adaptive interpolation (STR). Prediction is carried out using the Least Squares and Autoregressive (LS + AR). Our findings indicate that the two input formats, namely interpolating prior to column assignment in the idealized case and direct column assignment before interpolation in the real‐world environments, greatly affect prediction results. The former takes full advantage of the disclosed subsequent information, achieving a first‐day MAE of less than 0.1mas. The latter adheres to the actual conditions, resulting in a first‐day MAE above 0.2mas and performing worse than traditional forecasting. Additionally, we evaluated the forecasting performance using 6‐hr International GNSS Service Ultra‐rapid (IGU) inputs and found that it not only surpasses traditional methods but also outperforms USNO forecasts over the 1–10 days. Therefore, we do not recommend interpolating 24‐hr to 6‐hr, as interpolation is essentially a guess and does not provide meaningful information. This study only recommends using IGU‐6h derived from real observational data to obtain 6‐hr PM predictions. These findings can assist practical deep space exploration projects in making informed decisions when selecting 6‐hr PM predictions.

Geophysical sources and processes that excite the Earth’s Chandler wobble (CW) have long been debated. Significant discrepancies remain at times between geophysical fluid models, especially regarding inaccurate hydrological and cryospheric estimates, and observed CW series. Recently, the CW experienced anomalous behavior after 2015, with a disappearance and a re-excitation. Understanding hydrological and cryospheric effects on the CW and their contributions to this anomaly requires urgent investigation. Utilizing the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) measurements, we reconstruct the CW series contributed from the hydrology and cryosphere for the GRACE period (April 2002 to December 2015) and GFO period (June 2018 to December 2024), respectively. We find that GRACE/GFO measurements can capture more accurate hydrological and cryospheric forcing CW signals than models. For the first time, our reconstructed results successfully account for the recent observed disappearing and re-excited CW phenomenon. Considering global mass conservation associated with barystatic sea-level changes, the GRACE/GFO-derived hydrological and cryospheric effects agree well with geodetic CW observations. The absence of hydrological and cryospheric contributions on the reconstructed CW would lead to the unmanifested CW re-excitation phenomenon. Additionally, the relative contributions of the hydrology and cryosphere to CW amplitudes exhibit temporal variability, with ratios of approximately 3 to 1 and 2 to 1 during the GRACE and GFO periods, respectively. These findings improve our understanding of the Earth’s rotational dynamics under climate change in relation to the effects of hydrological and cryospheric processes.

The findings from the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC) suggest that integrating effective angular momentum (EAM) is vital for enhancing the accuracy of polar motion (PM) predictions. Building on Dill et al. (2021), https://doi.org/10.1029/2021ea002070, who identified systematic errors in the motion terms of atmospheric angular momentum (AAM), we discovered additional systematic errors in mass and motion terms of forecasts for the AAM, oceanic angular momentum (OAM) and hydrologic angular momentum (HAM), and promptly implemented corrections following their updates. During the hindcast experiment period from 20/5/2021 to 31/12/2023, and in the first three days in the X and Y directions, the proposed method showed advantages over the Helmholtz‐Centre Potsdam—German Research Centre for Geosciences (GFZ) and Eidgenössische Technische Hochschule Zürich (ETH Zürich). Then, the corrected EAM forecasts and reference values were used in the PM forecasting experiments, which showed no improvement, likely due to the existing PM forecasting system and overcompensation. However, when employing the perfect analysis of GEAM (the difference between geodesic angular momentum (GAM) and EAM), the proposed method herein achieves a maximum improvement of 30.0% and 55.5% in the X direction and 8.4% and 48.4% in the Y direction, compared to the official EAM forecasts of GFZ and ETH Zürich. This fully demonstrates that improvements in both EAM and GEAM are essential for enhancing PM predictions, and the EAM forecasts corrected by the proposed method are more competitive than those of GFZ and ETH Zürich.

Barystatic sea level stores excess water mass from the atmosphere and land to maintain global mass conservations within the Earth system. Besides the secular contribution to global sea‐level rise, changes in barystatic sea level also play an important role in mass‐induced length‐of‐day (LOD) variations over a few years or shorter periods. Compared to barystatic sea level changes deduced from the geophysical models, Gravity Recovery and Climate Experiment and GRACE follow‐on (GRACE/GFO) measurements provide actual observed ocean mass changes. Here, we investigate short‐term both seasonal (annual and semiannual) and non‐seasonal LOD variations caused by mass redistribution using GRACE/GFO mass estimates and effective angular momentum (EAM) products, particularly quantitatively assessing the excitation from the barystatic sea level. Note that correcting the problem of global mass non‐conservation is necessary for GRACE/GFO mass estimates in both spherical harmonic and mascon solutions to calculate the LOD excitation accurately. LOD mass term contributions derived from GRACE/GFO mass estimates considering global mass conservation show high consistency with satellite laser ranging results and are much closer to geodetic LOD observations than EAM products at seasonal and non‐seasonal time scales. The barystatic sea level exhibits the most significant amplitude in mass‐induced LOD variations, compensating for most land hydrological excitation, but shows no clear correlation with the atmosphere. Due to slight fluctuations in cryospheric effects and the substantial compensatory action of the barystatic sea level, differences in the land hydrological excitation do not lead to significant deviations in the total LOD mass term between EAM products and GRACE/GFO mass estimates.