Detection and modeling of nontidal oceanic effects on earth's rotation rate

Science

Volumn 281, Issue 5383, 1998, Pages 1656-1659

  Marcus, Steven L ^a   Chao, Yi ^a   Dickey, Jean O ^a   Gegout, Pascal ^a  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EARTH ROTATION; OCEANIC CIRCULATION; OCEANIC GENERAL CIRCULATION MODEL;

ARTICLE; ASTRONOMY; GLOBAL CLIMATE; OCEANIC REGIONS; PRIORITY JOURNAL; ROTATION; SEASONAL VARIATION; TEMPERATURE;

EID: 0032508539     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.281.5383.1656     Document Type: Article

References (32)

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4. Significant coherence between time series of LOD and AAM extends to periods as short as about 10 days, with loss of coherence at higher frequencies resulting from declining signal-to-noise ratios in both data types [J. O. Dickey, S. L Marcus, J. A. Steppe, R. Hide, Science 255, 321 (1992)].
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17. The OAM variation was calculated by assuming the spurious mass change to be distributed uniformly over the oceanic surface layer, following R. J. Greatbatch, J. Geophys. Res. 99, 12767 (1994). The results obtained by assuming the spurious mass change to be distributed uniformly over the oceanic interior are similar.
18. J. C. McWilliams, Annu. Rev. Fluid Mech. 28, 215 (1996); for a general discussion of Earth rotation excitation by geophysical fluids see R. T. H. Barnes, R. Hide, A. A. White, C. A. Wilson, Proc. R. Soc. London, Ser. A 387, 31 (1983). We found that the barotropic component of the MOM model produces OAM variations, which are very similar to the full MOM results, indicating a dominant role for barotropic dynamics in seasonal and shorter OAM variations. The rapid adjustment time of the barotropic modes [R. M. Ponte, J. Geophys. Res. 95, 11369 (1990)] enables the OGCMs to produce realistic OAM variations in spite of the incomplete equilibration of the model fields evident in Fig. 1, A and B.
19. J. C. McWilliams, Annu. Rev. Fluid Mech. 28, 215 (1996); for a general discussion of Earth rotation excitation by geophysical fluids see R. T. H. Barnes, R. Hide, A. A. White, C. A. Wilson, Proc. R. Soc. London, Ser. A 387, 31 (1983). We found that the barotropic component of the MOM model produces OAM variations, which are very similar to the full MOM results, indicating a dominant role for barotropic dynamics in seasonal and shorter OAM variations. The rapid adjustment time of the barotropic modes [R. M. Ponte, J. Geophys. Res. 95, 11369 (1990)] enables the OGCMs to produce realistic OAM variations in spite of the incomplete equilibration of the model fields evident in Fig. 1, A and B.
20. J. C. McWilliams, Annu. Rev. Fluid Mech. 28, 215 (1996); for a general discussion of Earth rotation excitation by geophysical fluids see R. T. H. Barnes, R. Hide, A. A. White, C. A. Wilson, Proc. R. Soc. London, Ser. A 387, 31 (1983). We found that the barotropic component of the MOM model produces OAM variations, which are very similar to the full MOM results, indicating a dominant role for barotropic dynamics in seasonal and shorter OAM variations. The rapid adjustment time of the barotropic modes [R. M. Ponte, J. Geophys. Res. 95, 11369 (1990)] enables the OGCMs to produce realistic OAM variations in spite of the incomplete equilibration of the model fields evident in Fig. 1, A and B.
21. R. S. Gross, in 1996 IERS Annual Report, M. Feissel, Ed. (Observatoire de Paris, France, 1997), p. 1129.
22. S. D. Desai, thesis, University of Colorado (1996).
23. AAM values were provided by the Sub-Bureau for Atmospheric Angular Momentum of the International Earth Rotation Service [D. A. Salstein, D. M. Kann, A. J. Miller, R. D. Rosen, Bull. Am. Meteorol. Soc. 74, 67 (1993)], based on operational analyses from ECMWF and JMA. Data from the NCEP/NCAR 40-Year Reanalysis Project were used to calculate the NCEP AAM series; see D. A. Salstein and R. D. Rosen, in 7th Conference on Climate Variations (American Meteorological Society, Boston, MA, 1997), p. 344. AAM values above 10 hPa were computed from gridded wind data taken from the UK Meteorological Office's Assimilated Data for Upper Atmosphere Research Satellite files and provided by the BADC; for details, see R. Swinbank and A. O'Neill, Mon. Weather Rev. 122, 686 (1994).
24. AAM values were provided by the Sub-Bureau for Atmospheric Angular Momentum of the International Earth Rotation Service [D. A. Salstein, D. M. Kann, A. J. Miller, R. D. Rosen, Bull. Am. Meteorol. Soc. 74, 67 (1993)], based on operational analyses from ECMWF and JMA. Data from the NCEP/NCAR 40-Year Reanalysis Project were used to calculate the NCEP AAM series; see D. A. Salstein and R. D. Rosen, in 7th Conference on Climate Variations (American Meteorological Society, Boston, MA, 1997), p. 344. AAM values above 10 hPa were computed from gridded wind data taken from the UK Meteorological Office's Assimilated Data for Upper Atmosphere Research Satellite files and provided by the BADC; for details, see R. Swinbank and A. O'Neill, Mon. Weather Rev. 122, 686 (1994).
25. AAM values were provided by the Sub-Bureau for Atmospheric Angular Momentum of the International Earth Rotation Service [D. A. Salstein, D. M. Kann, A. J. Miller, R. D. Rosen, Bull. Am. Meteorol. Soc. 74, 67 (1993)], based on operational analyses from ECMWF and JMA. Data from the NCEP/NCAR 40-Year Reanalysis Project were used to calculate the NCEP AAM series; see D. A. Salstein and R. D. Rosen, in 7th Conference on Climate Variations (American Meteorological Society, Boston, MA, 1997), p. 344. AAM values above 10 hPa were computed from gridded wind data taken from the UK Meteorological Office's Assimilated Data for Upper Atmosphere Research Satellite files and provided by the BADC; for details, see R. Swinbank and A. O'Neill, Mon. Weather Rev. 122, 686 (1994).
26. For the atmosphere, variations in axial angular momentum arising from moment-of-inertia changes are about an order of magnitude smaller than those driven by zonal winds (1) and involve mass fluctuations due to water vapor. Although these effects are large enough to significantly affect closure of the global budget, their consistent treatment requires full consideration of the hydrological cycle and is beyond the scope of this study.
27. R. Hide, in Dynamics of Earth's Deep Interior and Earth Rotation, J.-L. Le Mouel, D. E. Smylie, T. Herring, Eds. (American Geophysical Union, Washington, DC, 1993), pp. 109-112.
28. R. S. Gross, S. L. Marcus, T. M. Eubanks, J. O. Dickey, C. L. Keppenne, Geophys. Res. Lett. 23, 3373 (1996).
29. R. M. Ponte and R. D. Rosen, J. Phys. Oceanogr. 24, 1966 (1994); F. O. Bryan, Dyn. Atmos. Oceans 25, 191 (1997). Both of these studies found sizable annual signals in 1-year samples of OAM taken from OGCM runs forced by monthly mean climatological winds; however, no comparisons using synoptic geodetic or atmospheric data were made.
30. R. M. Ponte and R. D. Rosen, J. Phys. Oceanogr. 24, 1966 (1994); F. O. Bryan, Dyn. Atmos. Oceans 25, 191 (1997). Both of these studies found sizable annual signals in 1-year samples of OAM taken from OGCM runs forced by monthly mean climatological winds; however, no comparisons using synoptic geodetic or atmospheric data were made.
31. D. Hu and Y. Chao, Mon. Weather Rev., in press.
32. We thank M. Ghil, R. Gross, R. Hide, and two anonymous reviewers for useful comments on the manuscript. We are very grateful to D. Hu, who helped with the MICOM integration, and to D. Dong for the OAM calculation. Computations were performed on the Cray J-90 computer through the JPL Supercomputing project. The work of the authors was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.