-
10
-
-
0027788306
-
-
J. Tromp, ibid. 366, 678 (1993).
-
(1993)
Nature
, vol.366
, pp. 678
-
-
Tromp, J.1
-
12
-
-
0028869396
-
-
_, J. Geophys. Res. 100, 9805 (1995).
-
(1995)
J. Geophys. Res.
, vol.100
, pp. 9805
-
-
-
13
-
-
0028604743
-
-
L. Vinnik, B. Romanowicz, L, Berger, Geophys. Res. Lett. 21, 1671 (1994).
-
(1994)
Geophys. Res. Lett.
, vol.21
, pp. 1671
-
-
Vinnik, L.1
Romanowicz, B.2
Berger, L.3
-
14
-
-
0028830608
-
-
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
-
-
S. Karato, Science 262, 1708 (1993).
-
(1993)
Science
, vol.262
, pp. 1708
-
-
Karato, S.1
-
21
-
-
12644269175
-
-
note
-
-1.
-
-
-
-
22
-
-
12644290231
-
-
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
-
-
note
-
1, We inverted for the magnitude of anisotropy in the present study.
-
-
-
-
25
-
-
12644303173
-
-
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
-
-
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
-
-
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
-
-
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
-
-
note
-
1 imply unacceptably small values for the magnetic field in the core (20, 29, 31).
-
-
-
-
34
-
-
0029505490
-
-
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
-
-
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
-
-
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
-
-
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
-
-
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
-
-
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
-
-
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
-
-
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
-
-
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
-
-
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.
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