Estimation of Ocean Mass Redistribution by Means of Altimetry and Circulation Models and its Impact on the Gravity Field
With the upcoming new satellite missions CHAMP and GRACE, it will be possible for the first time to observe the time variable gravity field. Besides other sources, ocean mass redistribution is one of the major factors contributing to the overall time varying gravity signal. For estimating this time variable gravity signal, simulation studies with altimeter, sea surface temperature and ocean circulation data have been performed.
Monthly mean sea surface height models were computed over a period of three years combining altimetry and the corresponding mean sea surface temperature fields, which were used to remove the thermal water expansion. Based on these models monthly mass redistributions were computed in terms of water heights. The attraction of these water masses was computed and transformed into gravity field coefficients by spherical harmonic analysis with a resolution of up to degree 100 (corresponding to 400 km wavelength). By analyzing the complete monthly time series, amplitudes and phase lags for each of the spherical harmonic coefficients can be detected. Another method is the analysis of spherical harmonic coefficients derived from bottom pressure fields from the Parallel Ocean Circulation Model (POCM) up to degree and order 6 (provided by T. JOHNSON, CSR) for an 8 years period. Annual, semiannual and third annual amplitudes of variation of the Stokes coefficients are determined by Fourier analysis. The paper shows results of both simulation methods, their intercomparison, as well as comparisons with the expected error budget for both new gravity field missions.
KeywordsGravity Field Spherical Harmonic Coefficient Mass Redistribution Time Variable Gravity Gravity Field Solution
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- Colombo O.: Numerical methods for harmonic analysis on the sphere; The Ohio State University, Department of Geodetic Science, Report No. 310, Columbus/Ohio, 1981Google Scholar
- Reigber Ch., Lühr H., Kang Z., Schwintzer P.: The CHAMP mission and its role in observing temporal variations of the geopotential fields; Supplement to EOS Transactions of the American Geophysical Union, 78 (46), F163, 1997Google Scholar
- Tapley B.D.: The gravity recovery and climate experiment (GRACE); Supplement to EOS Transactions of the American Geophysical Union, 78 (46), F163, 1997Google Scholar