1. Determination of Gravity Variations in Northern Europe from GRACE Jürgen Müller, Matthias Neumann-Redlin Institut für Erdmessung, University of Hannover, Germany (mueller@ife.uni-hannover.de)mueller@ife.uni-hannover.de Meeting of NKG Geodynamics WG, March 2006, AS, Norway

2. Introduction GRACE Results Conclusions Contents

3. Observation of GIA-Induced Effects Land uplift (1 cm / year) Observed by - GPS - GRACE - terrestrial gravimetry  g = ± 2  Gal Scherneck et al., 2003

4. Difference Between Terrestrial and GRACE Data Absolute gravimetry - point-wise observations - also local and regional effects - high-frequency signals GRACE - spatial solution (spherical harmonics) - long spatial wavelengths - more low-frequency temporal signals appropriate reductions required as well as temporal and spatial filtering

5. GRACE Launch: March 2002 1cm-geoid with a spatial resolution of 200 km and temporal variations

6. Spectral Characteristics of Temporal Effects GRACE error curves compared to various signal curves Spectra provided by GFZ Potsdam GRACE

7. GRACE Monthly Solutions atmospheric and oceanic effects and tides already reduced using models

8. GRACE: Temporal Gravity Changes (L/2 = 1500 km) Residual signal (hydrology) [units:  Gal] Ocean, atmosphere Gravity differences of GRACE monthly solutions July – Sept. 2003 From CSR Solutions

9. Analysis of Monthly GRACE Solutions secular and periodic variations Least-squares adjustment t = months ω1 = 2π/6 = semi-annual period ω2 = 2π/12 = annual period A, B, C, D, E, F = unknowns Amp_6 = Amp_12 = Phase_12 = Trend = B Errors 13 nm/s² for gravity anomalies (Gauss filter 800 or 500 km) 4 nm/s²/yr for secular variations 3 nm/s² for amplitudes

10. Temporal Gravity Variations in Northern Europe Secular gravity variations (trend/year) as derived from GRACE data (Gauss filter 500 km) Bild Landhebung CSR (04/2002 – 03/2005)GFZ (02/2003 – 11/2005) -15 0 15 5 10 -5 -10 [μGal /year]

11. JPLGFZ Secular variations [μGal/a] CSR Period: 02/2003 – 03/2005 (21 months) Gaussian Filter: 500 km Comparison of Latest Releases

12. Different Gaussian Radii 500 km 600 km 700 km800 km GFZ (02/2003 – 11/2005)

13. Periodic Gravity Variations in Northern Europe [μGal] [nm/s²] Amplitudes semi-annual annual 500 km 800 km

14. annual phases Periodic Gravity Variations in Northern Europe (2) Months related to January

15. Contribution of Hydrology amplitudes semi-annual GRACE WGHM Amplitudes annual [nm/s²] 0 10 20 0 10 20 8 0 5 2 8 0 5 2

16. Contribution of Hydrology (2) GRACE Secular gravity variations per year WGHMGRACE-WGHM (period: April 2002 – June 2004) Both data show trend at the same location Signal is not in agreement with expected land uplift signal Further effects have to be considered -15 0 15 5 10 -5 -10 [nm/s² /year]

17. Comparison with further Hydrological Models WGHMGLDASLaDWorld GRACE-WGHM GRACE-LaDWorldGRACE-GLDAS [nm/s² /year] -15 0 15 5 10 -5 -10 -15 0 15 5 10 -5 -10 Secular gravity variations per year

18. Comparison with further Hydrological Models (2)

19. Absolute Gravity Results - Example Vaasa Onsala

20. Comparison with Absolute Gravity Data Absolute Gravity measurements with FG5-220 (IfE) Preliminary results, similar behaviour Further computations and investigations required VaasaOnsala

21. Determination of land uplift signal from GRACE data Procedure - Filtering of monthly GRACE solutions - Errors of reduction models - Models of further mass variations - Spatial and temporal analyses of residuals - Comparison with uplift models and independent data - Extension of test area and generalisation of results New Funding Project in Germany

22. Monthly solutions: January 2003 Different Representations of Gravity Gravity anomalies Gravity gradients [1/s²][m/s²]

23. Difference: January 2004 - 2003 anomalies gradients Different Representations of Gravity (2) [1/s²] [m/s²] Difference: 0.2 mE

24. Trend: Grace_Tzz (Gauss 500 km), [1/s 2 /year] Different Representations of Gravity (3) Difference: 0.06 mE/year

25. Secular Mass Variations Siberia WGHM_500_23GRACE_500_32 Trend caused by hydrological effects [water column in cm/a]

26. Determination of land uplift signal from GRACE data is very challenging – also from ground. Better GRACE models helpful Dedicated filtering and processing required Independent observations needed Inter-disciplinary cooperations indispensable Conclusions

27. Trend caused by hydrological effects [water column in cm/a] Secular Mass Variations in Eurasia GRACE_500_32 WGHM_500_23

28. GRACE_500_32 σ max ≈ 1,2 cm Annual amplitudes caused by hydrological effects [water column in cm/a] Annual Mass Variations Siberia