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Time-depending validation of ocean mass anomalies from GRACE by means of satellite altimetry and numerical models Henryk Dobslaw and Maik Thomas GeoForschungsZentrum.

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Presentation on theme: "Time-depending validation of ocean mass anomalies from GRACE by means of satellite altimetry and numerical models Henryk Dobslaw and Maik Thomas GeoForschungsZentrum."— Presentation transcript:

1 Time-depending validation of ocean mass anomalies from GRACE by means of satellite altimetry and numerical models Henryk Dobslaw and Maik Thomas GeoForschungsZentrum Potsdam Department 1 Geodesy and Remote Sensing Section 1.5 Earth System Modeling

2 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Motivation Comparison of GRACE gravity field time-series from indivdual processing centers with independent results from satellite altimetry and numerical modeling. reliability of GRACE observations homogeneity of the GRACE time-series accuracy at 500 km regional averages

3 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Method Jason 1OMCT Dobslaw & Thomas, JGR, 2007 GRACE observed mass anomalies observed sea surface height anomalies = mass anomalies + steric anomalies simulated mass anomalies GFZJPL CSRITG

4 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Monthly mean mass anomalies from GRACE Latest GRACE data available: GFZ Potsdam RL04JPL Pasadena RL04 CSR Austin RL04Univ. of Bonn ITG03p All GRACE data sets identically processed: - GAC product (atmosphere and ocean) added back - correlated error filter (Swenson and Wahr, GRL, 2006) - geocenter variations added (annual sine; Eanes, 2000) - continental leakage reduced according to Wahr et al., 1998 - Gaussian averaging filter: 500 km GFZJPL CSRITG

5 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Ocean Model for Circulation and Tides continental discharge runoff, drainage Ocean (OMCT) Atmosphere (ECMWF analyses) Continental surface (Land-Surface Scheme) River system (Hydrological Discharge Model) Sea-ice model wind stress, surface pressure, 2m-temperatures, precipitation, evaporation 2m-temperatures, precipitation Monthly mean ocean mass anomalies are simulated with OMCT. No additional smoothing has been applied.

6 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Monthly mean mass anomalies from Jason 1 Monthly mean sea surface height anomalies from Jason 1 processed at GFZ Potsdam (S. Esselborn). OMCT based steric anomalies have been subtracted. Transformation from sea surface height anomalies to mass anomalies by assuming a constant density of sea water (1031 kg/m 3 ). Spatial resolution has been assessed used autocorrelation function: Gaussian average filter 400 km have been applied. Data is currently available until June 2005 only.

7 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Data overview JanFebMarAprMayJunJulAugSepOctNovDec 2003xxxxxxxxxx 2004xxxxxxxxxxx 2005xxxxxx Jason 1OMCT GFZJPL CSRITG 27 monthly solutions from each data source corresponding means over all 27 months have been removed

8 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Rms differences – a first look GFZJPLCSRITG rms differences [hPa] Jason 1 - GFZJPL CSRITG

9 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Rms differences – a first look GFZJPL CSRITG Jason 1 rms differences [hPa] OMCT Aug – Oct 2004: increased rms differences for GFZ and JPL May 2003: increased rms differences for ITG rms differences [hPa]

10 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Mass anomalies [hPa] May 2003 Jason 1 GRACE SDS Newsletter Aug 2007: quality of accelerometer data degraded in June 2003 and only limited data available in May 2003 JPL OMCT GFZITGCSR

11 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Mass anomalies [hPa] September 2004 Jason 1 JPL OMCT GFZ ITGCSR GRACE SDS Newsletter Aug 2007: satellites temporarily in repeat orbit during Aug – Oct 2004

12 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Data overview JanFebMarAprMayJunJulAugSepOctNovDec 2003xxxxxxxxx 2004xxxxxxxx 2005xxxxxx Jason 1OMCT GFZJPL CSRITG 23 monthly solutions from each data source corresponding means over all 23 months have been removed

13 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE OMCT rms differences [hPa] Jason 1 rms differences [hPa] GFZJPL CSRITG March 2004: lowest rms differences Rms differences

14 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Mass anomalies [hPa] March 2004 Jason 1 JPL OMCT GFZ ITGCSR good correspondence in Southern Ocean tropics affected by correlated errors and uncertainties in steric correction applied to Jason 1

15 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Rms differences GFZJPL CSR rms differences [hPa] Jason 1 - GFZJPL CSRITG

16 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Correlation coefficients GFZJPL CSR ITG correlation coefficients Jason 1 - GFZJPL CSRITG

17 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE global non-tropics rmsGFZCSRJPLITG Jason 11.972.011.841.91 OMCT1.942.031.691.81 non-tropics and 500 km away from continents corr.GFZCSRJPLITG Jason 10.39 0.420.40 OMCT0.42 0.510.47 rmsGFZCSRJPLITG Jason 12.652.602.532.52 OMCT2.312.302.052.06 corr.GFZCSRJPLITG Jason 10.190.220.190.18 OMCT0.300.320.370.36 rmsGFZCSRJPLITG Jason 12.162.192.062.13 OMCT2.222.301.982.10 corr.GFZCSRJPLITG Jason 10.35 0.360.34 OMCT0.370.360.440.39 Overall statistics

18 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Conclusions For certain time-spans, the quality of GRACE observations is significantly degraded due to, e.g., accelerometer data problems or repeat orbit characteristics. The impact of these problems on the final gravity field solutions is considerable different depending on the processing scheme applied by the individual centers. Quality-degraded monthly fields have to be sorted out or have to be replaced by alternative (i.e. constrained) solutions. Regional ocean mass anomalies of 500 km averaging radius have been reliably obtained from all GRACE gravity field series, with JPL RL04 solutions generally performing best in this study.

19 Dobslaw and Thomas: Time-depending validation of ocean mass anomalies from GRACE Autocorrelation function

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