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  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic analysis of global tide gauge sea level data (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 100 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Yearly and monthly tide gauge sea level data from around the globe are fitted to numerically generated tidal data to search for the 18.6-yr lunar nodal tide and 14-month pole tide. Both tides are clearly evident in the results, with amplitudes and phases that are consistent with a global equilibrium response. Global atmospheric pressure data are fitted to global, monthly sea level data to study the response of the ocean to pressure fluctuations. The global response of sea level to pressure is found to be inverted barometer at periods greater than 2 months.A large coherence at 437 days between pressure and sea level data is found for the north Sea, Baltic Sea and the Gulf of Bothnia. The results are not entirely conclusive, but they tend to support O'Connor's (1986) suggestion that the apparent enhanced pole tide in these basins may be due to meteorological forcing rather than to a basin-scale resonance.Finally, global averages of tide gauge data, after correcting for the effects of post glacial rebound on individual station records, reveal an increase in sea level over the last 80 yr of between 1.1 and 1.9 mm yr−1. As part of the process of removing the effects of post-glacial rebound, we fit those effects to the global tide gauge data and obtain very good agreement with results predicted from post-glacial rebound models. This tends to support the post-glacial model results and it suggests that the global tide gauge data are, indeed, capable of resolving changes in sea level at the mm yr−1 level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb00697.x
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  • 2
    Electronic Resource
    Electronic Resource
    Aliasing and noise in core-surface flow inversions (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The potential pitfall that core flow inversions may be aliased as a result of model underparametrization is considered. Synthetic tests involving randomly generated flows with differing energy spectra have been used to explore this problem. If underparametrizing neglects terms comparable to the largest of those already modelled, only a poor representation (not an average in space or time) of the actual flow that generated the data is obtained. It is found that the key aspects of the flow that determine whether an underparametrized inversion of the field produced by that flow will be successful are its temporal and spatial energy spectra: when the spectra fall off as (degree)−2, or faster, underparametrized inversions yield accurate results, but if the decrease is slower, the spatial and/or temporal aliasing is severe enough to corrupt the solution at all degrees. Damping does not appear 10 remedy this difficulty but in fact obscures it by forcing the flow to converge upon a single, but possibly still aliased, solution. Guided by this analysis, the ‘ufm1’ radial field model of Bloxham & Jackson (1992) was inverted for core-surface flows between 1970 and 1990. Parametrizing the flow as steady in time leads to solutions that are highly sensitive to the model truncation level. It appears that temporal (but not spatial) underparametrization and the aliasing this induces is to blame. Relaxing the steady-motion constraint produces estimates displaying convergence in the temporal domain and greatly reduces sensitivity to spatial truncation level. The core flow shows significant temporal variation, even over an interval as short as 20 years. The resulting energy spectra, however, are still too flat to be those of the true flow without incurring severe spatial aliasing that is not observed. It appears that noise in the high-degree secular variation (SV) is responsible. Damping is effective in removing most of this noise, but only because aliasing is no longer a factor and noise is restricted to that part of the SV signal which makes only a small contribution to the flow solution. Finally, tests with synthetic fields, generated by known flows and perturbed with noise, reveal that the level of real noise present in the high-degree SV may be as much as 102 times larger than the ufm1 SV convariance estimates indicate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb05302.x
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  • 3
    Electronic Resource
    Electronic Resource
    Taking into account truncation problems and geomagnetic model accuracy in assessing computed flows at the core-mantle boundary (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 108 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: SUMMARYSince the time Roberts & Scott (1965) first expressed the key ‘frozen flux’ hypothesis relating the secular variation of the geomagnetic field (SV) to the flow at the core surface, a large number of studies have been devoted to building maps of the flow and inferring its fundamental properties from magnetic observations at the Earth's surface. There are some well-known difficulties in carrying out these studies, such as the one linked to the non-uniqueness of the flow solution [if no additional constraint is imposed on the flow (Backus 1968)] which has been thoroughly investigated. In contrast little investigation has been made up to now to estimate the exact importance of other difficulties, although the different authors are usually well aware of their existence. In this paper we intend to make as systematic as possible a study of the limitations linked to the use of truncated spherical harmonic expansions in the computation of the flow. Our approach does not rely on other assumptions than the frozen flux, the insulating mantle and the large-scale flow assumptions along with some simple statistical assumptions concerning the flow and the Main Field. Our conclusions therefore apply to any (toroidal, steady or tangentially geostrophic) of the flow models that have already been produced; they can be summarized in the following way: first, because of the unavoidable truncation of the spherical harmonic expansion of the Main Field to degree 13, no information will ever be derived for the components of the flow with degree larger than 12; second, one may truncate the spherical harmonic expansion of the flow to degree 12 with only a small impact on the first degrees of the flow. Third, with the data available at the present day, the components of the flow with degree less than 5 are fairly well known whereas those with degree greater than 8 are absolutely unconstrained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00852.x
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  • 4
    Electronic Resource
    Electronic Resource
    The Earth's Rotation (1988)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Earth and Planetary Sciences 16 (1988), S. 231-249 
    Details
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ea.16.050188.001311
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  • 5
    Electronic Resource
    Electronic Resource
    The possibility of lateral structure inside the core and its implications for nutation and Earth tide observations (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 99 (1989), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We show that there can be lateral structure inside the fluid core caused by gravitational forcing from the mantle, from the inner core, or from topography on the core–mantle or inner core–outer core boundaries. We describe a method for calculating the internal structure, given knowledge of the forcing. We discuss the possible effects of this structure on results for the core–mantle boundary topography inferred from observations of the Earth's forced nutations and diurnal earth tides. We consider the possible implications of a thin, low-density fluid layer at the top of the core.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1989.tb02036.x
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  • 6
    Electronic Resource
    Electronic Resource
    Internal Loading of an Inhomogeneous Compressible Earth With Phase Boundaries (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 125 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We use an approach described by Dehant & Wahr (1991) to estimate the geoid and boundary topography caused by mass loads inside the Earth. We show how the estimates are affected by compressibility and a radially varying density distribution, and by the presence of phase boundaries with density discontinuities. We compare results for earth models that have a chemical boundary at 670 km depth with those that have a phase boundary at that depth. We find that the 670 km topographies predicted for models with a chemical boundary are several times larger than for models with a phase boundary, depending principally on the value of the Clapeyron slope in the phase case. the geoid predicted in the chemical boundary case is about 30–40 per cent smaller than that predicted in the phase case. the effects of compressibility and radially varying density are likely to be small. We estimate the laterally varying structure inside the fluid core by computing the topography on constant-potential surfaces within the core. We conclude that this structure is not likely to be a complicating factor when using nutation and Earth tide observations to estimate the flattening of the core-mantle boundary. Finally. we compute the inner core-outer core (icb) topography for loading inside the mantle and for loading inside the inner core. We show that in the first case, the icb topography is small and dominated by long wavelengths; in the second case, we conclude that, if the density heterogeneities inside the inner core are two orders of magnitude smaller than in the mantle, the icb topography can be about 100 m peak-to-peak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb06544.x
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  • 7
    Electronic Resource
    Electronic Resource
    Secular changes in rotation and gravity: Evidence of post-glacial rebound or of changes in polar ice?
    Amsterdam : Elsevier
    Advances in Space Research 13 (1993), S. 257-269 
    Details
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0273-1177(93)90228-4
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  • 8
    Electronic Resource
    Electronic Resource
    Detailed investigation of a spot on the core mantle boundary using digital PcP data
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 68 (1991), S. 132-143 
    Details
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(91)90013-8
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  • 9
    Electronic Resource
    Electronic Resource
    Core-mantle interactions (1990)
    Springer
    Surveys in geophysics 11 (1990), S. 329-353 
    Details
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Several aspects of core-mantle interactions were considered during a Royal Astronomical Society Discussion Meeting on 12th May 1989, including modelling the geomagnetic field at the core surface, the morphology of the field between 1600 and 1820 AD, dynamo theory, Taylor's constraint, fluid motions at the top of the core that reproduce the observed secular variation, pressure coupling between the core and mantle and its geophysical consequences, topographic core-mantle coupling, angular momentum transfer at the core-mantle interface, the detection and implications of core oscillations, particularly those with associated fluctuations in the Earth's rotation rate, and the seismological determination of the core-mantle boundary topography from lateral inhomogeneities in the mantle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01902965
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  • 10
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    Sea level is rising: Do we know why? (2002)
    National Academy of Sciences
    Details
    Publication Date: 2002-05-14
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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