메뉴 건너뛰기




Volumn 274, Issue 5294, 1996, Pages 1883-1887

Planet within a planet: Rotation of the inner core of earth

Author keywords

[No Author keywords available]

Indexed keywords

ANISOTROPY; ARTICLE; ASTRONOMY; MAGNETIC FIELD; PRIORITY JOURNAL; ROTATION; TIME;

EID: 0030448620     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.274.5294.1883     Document Type: Article
Times cited : (158)

References (49)
  • 10
    • 0027788306 scopus 로고
    • J. Tromp, ibid. 366, 678 (1993).
    • (1993) Nature , vol.366 , pp. 678
    • Tromp, J.1
  • 12
    • 0028869396 scopus 로고
    • _, J. Geophys. Res. 100, 9805 (1995).
    • (1995) J. Geophys. Res. , vol.100 , pp. 9805
  • 14
    • 0028830608 scopus 로고
    • o equation presented where δ, and φ, are the coordinates of the ith CAS average. The CAS approach enhances the effect of anisotropy with respect to, for example, random reading errors or any signal that might result from lateral heterogeneity in the inner core. The PKIKP or DF branch, which defines the rays entering the inner core (Fig. 1A), is used to measure the inner-core anisotropy. Because of the interference of travel times belonging to different branches of the core phases (Fig. 1, A and B), the DF branch arrivals cannot be reliably measured in the full distance range of interest. At large distances (approaching 180°), there are few measurements because of the small area at Earth's surface where observations can be made.
    • (1995) J. Geophys. Res. , vol.100 , pp. 9831
    • Su, W.-J.1    Dziewonski, A.M.2
  • 17
    • 0027753732 scopus 로고
    • S. Karato, Science 262, 1708 (1993).
    • (1993) Science , vol.262 , pp. 1708
    • Karato, S.1
  • 21
    • 12644269175 scopus 로고    scopus 로고
    • note
    • -1.
  • 22
    • 12644290231 scopus 로고    scopus 로고
    • note
    • tm are fully normalized associated Legendre polynomials. We formulate a nonlinear least-squares problem in which we find the coefficients Xt1 and Blm and the frequency ω for which the best variance reduction is achieved. Using the coefficients derived from the data shown in Fig. 2. we find that this formulation is not appropriate: The maximum variance reduction is obtained for ω = 0. This means that, in addition to the variable part (only m ≠ 0 terms are involved), there must be also be a part of the rotation (off-)axis velocity pattern that does not depend on time.
  • 24
    • 12644250054 scopus 로고    scopus 로고
    • note
    • 1, We inverted for the magnitude of anisotropy in the present study.
  • 25
    • 12644303173 scopus 로고    scopus 로고
    • note
    • 1, whose sum has a maximum at -60°N. Thus, observations at corresponding values of the angle ζ, the angle that a ray forms with the axis of symmetry, should be the best for monitoring the rotation of the inner core. This is confirmed in Fig. 4D, which shows the time derivative of Fig. 4C (the relatively large effects predicted for low latitudes may be contaminated by noise, because the CAS coverage below 30° has had large gaps during the early time intervals; Fig. 2). The predicted solutions for the earliest and latest time periods compare well with the data (Fig. 4, E and F) as well as with the spherical-harmonic expansion for the same time periods (Fig. 2, A and F).
  • 27
    • 0003756159 scopus 로고
    • Oxford Univ. Press, New York
    • K. Lambeck, The Earth's Variable Rotation: Geophysical Causes and Consequences (Cambridge Univ. Press, New York, 1980); Geophysical Geodesy: The Slow Deformations of the Earth (Oxford Univ. Press, New York, 1988).
    • (1988) Geophysical Geodesy: The Slow Deformations of the Earth
  • 28
    • 12644284475 scopus 로고    scopus 로고
    • note
    • 2, is an average for the past 2 millennia and has varied by <50% over this time period (26). Because of the need for a large backward extrapolation in time, however, its uncertainty for the present application is difficult to evaluate.
  • 31
    • 0023509059 scopus 로고
    • J. A. Jacobs, Ed. Academic Press, Orlando, FL
    • D. Gubbins and P. H. Roberts, in Geomagnetism, J. A. Jacobs, Ed. (Academic Press, Orlando, FL, 1987), vol. 2, pp. 1-23.
    • (1987) Geomagnetism , vol.2 , pp. 1-23
    • Gubbins, D.1    Roberts, P.H.2
  • 32
    • 12644266305 scopus 로고    scopus 로고
    • note
    • 1 imply unacceptably small values for the magnetic field in the core (20, 29, 31).
  • 34
    • 0029505490 scopus 로고
    • G. A. Glatzmaier and P. H. Roberts, Nature 377, 203 (1995); Phys. Earth Planet. Inter. 91, 63 (1995).
    • (1995) Phys. Earth Planet. Inter. , vol.91 , pp. 63
  • 36
    • 12644291151 scopus 로고    scopus 로고
    • note
    • In the Glatzmaier-Roberts model (31), the eastward rotation of the inner core relative to the mantle is maintained by magnetic coupling between the solid inner core and the fluid just above it, which is flowing eastward because of a thermal-wind effect (G. A. Glatzmaier, personal communication). As in their original simulation, their latest results show an east-ward rotation of the inner core that varies in magnitude between 2° and 3° year 1 relative to the mantle.
  • 37
    • 0019923573 scopus 로고
    • S. R. C. Malin and B, M. Hodder, Nature 296, 726 (1982): M. G. McLeod, J. Geophys. Res. 90, 4597 (1985)
    • (1982) Nature , vol.296 , pp. 726
    • Malin, S.R.C.1    Hodder, B.M.2
  • 38
    • 0008376515 scopus 로고
    • S. R. C. Malin and B, M. Hodder, Nature 296, 726 (1982): M. G. McLeod, J. Geophys. Res. 90, 4597 (1985)
    • (1985) J. Geophys. Res. , vol.90 , pp. 4597
    • McLeod, M.G.1
  • 39
    • 0027795092 scopus 로고
    • 4 m into the inner core within a century (20, 29, 38); see also R. Hollerbach and C. A. Jones, Nature 385, 541 (1993).
    • (1993) Nature , vol.385 , pp. 541
    • Hollerbach, R.1    Jones, C.A.2
  • 40
    • 12644311233 scopus 로고    scopus 로고
    • note
    • Scaling analysis between the core and atmosphere shows that a few years' seismological monitoring of the inner-core motion corresponds to hourly observations of the weather.
  • 46
    • 0000451621 scopus 로고
    • E. R. Benton and A. Clark Jr., Annu. Rev. Fluid Mech. 6, 257 (1974): see also D, E. Loper, Phys. Fluids 13, 2995 (1970); R. G. Davis, Geophys. Res. Lett. 21, 1815 (1994).
    • (1974) Annu. Rev. Fluid Mech. , vol.6 , pp. 257
    • Benton, E.R.1    Clark Jr., A.2
  • 47
    • 0005550211 scopus 로고
    • E. R. Benton and A. Clark Jr., Annu. Rev. Fluid Mech. 6, 257 (1974): see also D, E. Loper, Phys. Fluids 13, 2995 (1970); R. G. Davis, Geophys. Res. Lett. 21, 1815 (1994).
    • (1970) Phys. Fluids , vol.13 , pp. 2995
    • Loper, D.E.1
  • 48
    • 0028668846 scopus 로고
    • E. R. Benton and A. Clark Jr., Annu. Rev. Fluid Mech. 6, 257 (1974): see also D, E. Loper, Phys. Fluids 13, 2995 (1970); R. G. Davis, Geophys. Res. Lett. 21, 1815 (1994).
    • (1994) Geophys. Res. Lett. , vol.21 , pp. 1815
    • Davis, R.G.1
  • 49
    • 12644262344 scopus 로고    scopus 로고
    • note
    • We thank G. Glatzmaier, D. Loper, M. Manga, P, Olson, P, H. Roberts, B. Romanowicz, L. Stixrude, J, Tromp. and G. Ekström for helpful discussions, as well as X.-D. Song and P. G. Richards for sending us a copy of their paper before publication and for subsequent discussions. This work was initiated while A.M. D. was a visiting professor in the Miller Institute for Basic Research in Science (March 1995) and was supported by NSF and NASA.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.