Journal metrics

Journal metrics

  • IF value: 4.165 IF 4.165
  • IF 5-year value: 4.075 IF 5-year 4.075
  • CiteScore value: 4.28 CiteScore 4.28
  • SNIP value: 1.501 SNIP 1.501
  • SJR value: 1.060 SJR 1.060
  • IPP value: 4.21 IPP 4.21
  • h5-index value: 29 h5-index 29
  • Scimago H index value: 27 Scimago H index 27
Volume 9, issue 2 | Copyright

Special issue: Dynamics and interaction of processes in the Earth and its...

Solid Earth, 9, 323-339, 2018
https://doi.org/10.5194/se-9-323-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 23 Mar 2018

Research article | 23 Mar 2018

Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits

Christina Lück, Jürgen Kusche, Roelof Rietbroek, and Anno Löcher Christina Lück et al.
  • Institute of Geodesy and Geoinformation, University of Bonn, Bonn, Germany

Abstract. Measuring the spatiotemporal variation of ocean mass allows for partitioning of volumetric sea level change, sampled by radar altimeters, into mass-driven and steric parts. The latter is related to ocean heat change and the current Earth's energy imbalance. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has provided monthly snapshots of the Earth's time-variable gravity field, from which one can derive ocean mass variability. However, GRACE has reached the end of its lifetime with data degradation and several gaps occurred during the last years, and there will be a prolonged gap until the launch of the follow-on mission GRACE-FO. Therefore, efforts focus on generating a long and consistent ocean mass time series by analyzing kinematic orbits from other low-flying satellites, i.e. extending the GRACE time series.

Here we utilize data from the European Space Agency's (ESA) Swarm Earth Explorer satellites to derive and investigate ocean mass variations. For this aim, we use the integral equation approach with short arcs (Mayer-Gürr, 2006) to compute more than 500 time-variable gravity fields with different parameterizations from kinematic orbits. We investigate the potential to bridge the gap between the GRACE and the GRACE-FO mission and to substitute missing monthly solutions with Swarm results of significantly lower resolution. Our monthly Swarm solutions have a root mean square error (RMSE) of 4.0mm with respect to GRACE, whereas directly estimating constant, trend, annual, and semiannual (CTAS) signal terms leads to an RMSE of only 1.7mm. Concerning monthly gaps, our CTAS Swarm solution appears better than interpolating existing GRACE data in 13.5% of all cases, when artificially removing one solution. In the case of an 18-month artificial gap, 80.0% of all CTAS Swarm solutions were found closer to the observed GRACE data compared to interpolated GRACE data. Furthermore, we show that precise modeling of non-gravitational forces acting on the Swarm satellites is the key for reaching these accuracies. Our results have implications for sea level budget studies, but they may also guide further research in gravity field analysis schemes, including satellites not dedicated to gravity field studies.

Download & links
Publications Copernicus
Special issue
Download
Short summary
Since 2002, the GRACE mission provides estimates of the Earth's time-variable gravity field, from which one can derive ocean mass variability. Now that the GRACE mission has come to an end, it is especially important to find alternative ways for deriving ocean mass changes. For the first time, we use kinematic orbits of Swarm for computing ocean mass time series. We compute monthly solutions, but also show an alternative way of directly estimating time-variable spherical harmonic coefficients.
Since 2002, the GRACE mission provides estimates of the Earth's time-variable gravity field,...
Citation
Share