We analyze the impact of large earthquakes on the estimation of the global mean ocean mass (GMOM) change rate over the 13-year period (January 2003 to December 2015) using the Gravity Recovery and Climate Experiment (GRACE) Release-06 (RL06) monthly gravity solutions released by the Center for Space Research (CSR). We take into account the effects of the December 2004 Mw9.1 and April 2012 Mw8.6 Sumatra earthquakes, the March 2011 Mw9.0 Tohoku-Oki earthquake, and the February 2010 Mw8.8 Chile earthquake. After removing the co- and post-seismic effects of these earthquakes in the oceanic areas by least squares fitting, we estimate the GMOM rate from GRACE monthly observations. Results show that GRACE-observed GMOM rate before the seismic correction is 2.12 ± 0.30 mm/year, while after correction the rate is 2.05 ± 0.30 mm/year. Even though the −0.07 ± 0.02 mm/year seismic influence on GRACE GMOM rate is small on a global scale, it is a systematic bias and should be considered for improved quantification and understanding of the global sea level change.

The Earth's shape is much closer to an ellipsoid than a sphere. The commonly used spherical approximation in mass change inversion is expected to cause bias by the spherical harmonic (SH) solutions from Gravity Recovery and Climate Experiment (GRACE), especially in high‐latitude regions where significant present‐day ice losses occur. This bias, or ellipsoidal correction, reaches up to 8% from the evaluation by simulations based on synthetic mass change rate models. Further evaluation using 14 plus years of GRACE monthly SH solutions (from April 2002 to December 2016) indicates that the ellipsoidal correction is also noticeable in the total mass change time series over polar regions. Before and after the ellipsoidal correction, the estimated linear rates from mass change time series differ by 4.3%, 4.7%, 5.2%, 5.7%, and 6.6% for five selected regions over Greenland, Antarctic Peninsula, Amundsen Sea Embayment, Alaska glacier, and Svalbard Islands, respectively. Although with amplitudes likely below the current GRACE's uncertainty level, these differences are consistently negative over the five regions. This indicates that the spherical approximation leads to systematic underestimation for polar mass change rates. Thus, the ellipsoidal correction needs to be considered for more precise mass recovery with GRACE SH solutions. It also depends on spatial scales of mass change signals (the smaller the spatial scale, the larger the correction). To more reliably estimate high‐latitude surface mass changes by GRACE SH solutions, the ellipsoidal correction is recommended, especially for ice‐loss signals over polar regions.

We examine vertical load deformation at four continuous Global Positioning System (GPS) sites in southern Greenland relative to Gravity Recovery and Climate Experiment (GRACE) predictions of vertical deformation over the period 2002–2016. With limited spatial resolution, GRACE predictions require adjustment before they can be compared with GPS height time series. Without adjustment, both GRACE spherical harmonic (SH) and mascon solutions predict significant vertical displacement rate differences relative to GPS. We use a scaling factor method to adjust GRACE results, based on a long-term mass rate model derived from GRACE measurements, glacial geography, and ice flow data. Adjusted GRACE estimates show significantly improved agreement with GPS, both in terms of long-term rates and interannual variations. A deceleration of mass loss is observed in southern Greenland since early 2013. The success at reconciling GPS and GRACE observations with a more detailed mass rate model demonstrates the high sensitivity to load distribution in regions surrounding GPS stations. Conversely, the value of GPS observations in constraining mass changes in surrounding regions is also demonstrated. In addition, our results are consistent with recent estimates of GIA uplift (∼4.4 mm yr⁻¹) at the KULU site.

We compute the vertical displacements in the Amazon Basin using the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) observations, including both the gravity spherical harmonic (SH) solutions from the Center for Space Research (CSR), GeoForschungsZentrum (GFZ) and Jet Propulsion Laboratory (JPL) and mascons from CSR, JPL and Goddard Space Flight Center (GSFC). The correlation coefficients, annual amplitude and root mean squares (RMS) reductions are calculated to assess the agreements between the GRACE/GRACE-FO and Global Navigation Satellite System (GNSS) vertical displacements at 22 selected GNSS stations. For the six GRACE/GRACE-FO products (i.e., CSR SH, GFZ SH, JPL SH, CSR mascon, GSFC mascon and JPL mascon), the mean annual amplitude reductions are 77.6%, 76.4%, 76.3%, 78.6%, 78.5% and 76.6%, respectively, the corresponding mean RMS reductions are 63.2%, 61.7%, 62.3%, 64.9%, 65.3% and 63.8%, respectively, and the mean correlation coefficients are all over 0.93. On the whole, mascon solutions agree slightly better with GNSS solutions than SH solutions do. The CSR SH and the GSFC mascon solutions show the best agreements with the GNSS solution among the 3 SH and 3 mascon products, respectively. We estimate GRACE/GRACE-FO noises using the three-cornered hat (TCH) method and find that the CSR SH and GSFC mascons also have the smallest noise variances among the SH and mascon products, respectively. By analyzing the GNSS stations from the central and southern Amazon Basin, we find that: (1) the RMS reductions when the mascon solutions are removed from GNSS height series are slightly larger than those using the SH solutions in the center, while in south all the RMS reductions are fairly close; (2) for both SH solutions and mascon solutions, the correlation coefficients in the center are slightly larger than those in the south, but conversely, the mean annual amplitude reductions in the center are much smaller than those in the south.

We carry out synthetic experiments of mass load inversion using Global Navigation Satellite System (GNSS) vertical and horizontal displacements in Central China. Using two synthetic mass load models from a checkerboard mass distribution and a more realistic distribution derived from the Gravity Recovery and Climate Experiment (GRACE) observations, the inverted mass changes are determined based on the load theory and then compared with the known mass‐change inputs. We find that the combination of horizontal displacements with the commonly used vertical displacements significantly improves the inversion results when the number of sites is larger than one third of the number of total grids with relatively uniform distribution over the region. Synthetic tests demonstrate that data from the Crustal Movement Observation Network of China, including the total number of GNSS sites, spatial distribution, and precision, are sufficient to infer the annual amplitudes of mass changes in the region with comparable spatial resolution as that of GRACE observations. For the current precision level of the GNSS surface displacements (3.0 mm in the vertical and 1.0 mm in the horizontal components), including horizontal displacements leads to ∼10% improvement in mass inversion, compared to using vertical displacements only. With a higher precision level of 0.50 and 0.17 mm (for vertical and horizontal components, respectively), an improvement of ∼20% can be achieved.

We analyze satellite altimeter observed Caspian Sea level (CSL) changes over the period January 1993 to December 2021 using the lake level series from the Hydroweb project and global sea level anomalies (SLA) grids provided by the Copernicus Marine Environment Monitoring Service (CMEMS). The two altimeter-based CSL series agree well at interannual and longer time scales, but show significantly large discrepancies at seasonal and shorter time scales. The large discrepancies are found to be introduced by the approximately inverted barometer (IB) correction applied to the CMEMS SLA over the Caspian Sea. The IB correction over the Caspian Sea or any enclosed lakes needs to be treated separately from the ocean by using the correct reference mean pressure. The actual IB effects over the Caspian Sea are significantly smaller than those applied in the CMEMS SLA grids. After applying an improved IB correction using the global mean sea level pressure fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis atmospheric model, the two CSL series agree remarkably well. Altimeter observed CSL series show a significant decreasing trend on top of strong seasonal variations. The estimated linear trends for the Hydroweb and CMEMS CSL series are −5.37 ± 0.11 and −5.40 ± 0.11 cm/yr, respectively. Annual amplitudes are 17.03 ± 1.33 vs. 15.79 ± 1.30 cm, with nearly the same phases. The CSL change shows notable acceleration in the decreasing trend since around 2005, and the estimated trends have increased to −8.86 ± 0.10 and −8.81 ± 0.10 cm/yr, respectively for the two-altimeter CSL series.