GHOST: Geoscientific Hollow Sphere Tessellation

Thieulot, Cédric

doi:10.5194/se-9-1169-2018

Cited by 4 publications

(3 citation statements)

References 51 publications

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“…On the contrary, when density distribution models are to be used along with gravity, a common choice is to use grids that allow for accurate and fast volume integration -this especially holds for equi-angular grids as surface elements can easily be translated into volume elements (tesseroid). Note that the choice of the data representation on the sphere for different data types is still a subject of active research in fields like geophysics (Thieulot, 2018), astrophysics, computer visualization, and mathematics.…”

Section: Methods: Gravity Integration Techniquesmentioning

confidence: 99%

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Benchmark forward gravity schemes: the gravity field of a realistic lithosphere model WINTERC-G

et al. 2022

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Abstract. Several alternative gravity forward modelling methodologies and associated numerical codes with their own advantages and limitations are available for the solid Earth community. With upcoming state-of-the-art lithosphere density models and accurate global gravity field data sets, it is vital to understand the opportunities and limitations of the various approaches. In this paper, we discuss the four widely used techniques: global spherical harmonics (GSH), tesseroid integration (TESS), triangle integration (TRI), and hexahedral integration (HEX). A constant density shell benchmark shows that all four codes can produce similar precise gravitational potential fields. Two additional shell tests were conducted with more complicated density structures: laterally varying density structures and a crust–mantle interface density. The differences between the four codes were all below 1.5 % of the modelled gravity signal suitable for reproducing satellite-acquired gravity data. TESS and GSH produced the most similar potential fields (<0.3 %). To examine the usability of the forward modelling codes for realistic geological structures, we use the global lithosphere model WINTERC-G that was constrained, among other data, by satellite gravity field data computed using a spectral forward modelling approach. This spectral code was benchmarked against the GSH, and it was confirmed that both approaches produce a similar gravity solution with negligible differences between them. In the comparison of the different WINTERC-G-based gravity solutions, again GSH and TESS performed best. Only short-wavelength noise is present between the spectral and tesseroid forward modelling approaches, likely related to the different way in which the spherical harmonic analysis of the varying boundaries of the mass layer is performed. The spherical harmonic basis functions produce small differences compared to the tesseroid elements, especially at sharp interfaces, which introduces mostly short-wavelength differences. Nevertheless, both approaches (GSH and TESS) result in accurate solutions of the potential field with reasonable computational resources. Differences below 0.5 % are obtained, resulting in residuals of 0.076 mGal standard deviation at 250 km height. The biggest issue for TRI is the characteristic pattern in the residuals that is related to the grid layout. Increasing the resolution and filtering allow for the removal of most of this erroneous pattern, but at the expense of higher computational loads with respect to the other codes. The other spatial forward modelling scheme, HEX, has more difficulty in reproducing similar gravity field solutions compared to GSH and TESS. These particular approaches need to go to higher resolutions, resulting in enormous computation efforts. The hexahedron-based code performs less than optimal in the forward modelling of the gravity signature, especially with a laterally varying density interface. Care must be taken with any forward modelling software as the approximation of the geometry of the WINTERC-G model may deteriorate the gravity field solution.

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Section: Methods: Gravity Integration Techniquesmentioning

confidence: 99%

“…The (default) topology of the mesh in ASPECT is shown in Fig. 3, which is based on a decomposition of the sphere into six identical regions as described in Thieulot (2018). In the case of the shell tests described in the following section, a single element is used in the radial direction.…”

Section: Description Of the Gravity Post-processor In The Aspect Codementioning

confidence: 99%

Benchmark forward gravity schemes: the gravity field of a realistic lithosphere model WINTERC-G

et al. 2022

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“…Varying cell-area may be important to compare the outcome of a numerical model with datasets that have very different resolutions (e.g., seismology versus geochemistry). We illustrate different cell resolutions with our 2D example model, but a similar approach may be used for a 3D model albeit with a different tessellation (Thieulot, 2018). The lowest resolution (10x40) contains 40 cells along the CMB, increasing across the 10 layers to 68 cells along the surface, for a global total of 539 cells (Fig.…”

Section: Cell Distributionmentioning

confidence: 99%

Quantifying mantle mixing through configurational Entropy

van der Wiel,

Thieulot,

van Hinsbergen

2023

Preprint

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Geodynamic models of mantle convection provide a powerful tool to obtain insights into the structure and composition of the Earth’s mantle that resulted from a long history of differentiating and mixing. Comparing such models with geophysical and geochemical observations is challenging as these datasets often sample entirely different temporal and spatial scales. Here, we explore the use of configurational entropy, based on tracer and compositional distribution on a global and local scale. We show means to calculate configurational entropy in a 2D annulus and find that these calculations may be used to quantitatively compare long-term geodynamic models with each other. The entropy may be used to analyze, with a single measure, the mixed state of the mantle as a whole and may also be useful to validate numerical models against local anomalies in the mantle that may be inferred from seismological or geochemical observations.

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Changes in core–mantle boundary heat flux patterns throughout the supercontinent cycle

Dannberg,

Gassmöller,

Thallner

et al. 2024

Geophysical Journal International

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Summary The Earth’s magnetic field is generated by a dynamo in the outer core and is crucial for shielding our planet from harmful radiation. Despite the established importance of the core-mantle boundary heat flux as driver for the dynamo, open questions remain about how heat flux heterogeneities affect the magnetic field. Here, we explore the distribution of core-mantle boundary heat flux on Earth and its changes over time using compressible global 3-D mantle convection models in the geodynamic modeling software ASPECT. We discuss the use of the consistent boundary flux method as a tool to more accurately compute boundary heat fluxes in finite element simulations and the workflow to provide the computed heat flux patterns as boundary conditions in geodynamo simulations. Our models use a plate reconstruction throughout the last 1 billion years—encompassing the complete supercontinent cycle—to determine the location and sinking speed of subducted plates. The results show how mantle upwellings and downwellings create localized heat flux anomalies at the core-mantle boundary that can vary drastically over Earth’s history and depend on the properties and evolution of the lowermost mantle as well as the surface subduction zone configuration. The distribution of hot and cold structures at the core-mantle boundary changes throughout the supercontinent cycle in terms of location, shape and number, indicating that these structures fluctuate and might have looked very differently in Earth’s past. We estimate the resulting amplitude of spatial heat flux variations, expressed by the ratio of peak-to-peak amplitude to average heat flux, q*, to be at least 2. However, depending on the material properties and the adiabatic heat flux out of the core, q* can easily reach values >30. For a given set of material properties, q* generally varies by 30-50% over time. Our results have implications for understanding the Earth’s thermal evolution and the stability of its magnetic field over geological timescales. They provide insights into the potential effects of the mantle on the magnetic field and pave the way for further exploring questions about the nucleation of the inner core and the past state of the lowermost mantle.

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GHOST: Geoscientific Hollow Sphere Tessellation

Cited by 4 publications

References 51 publications

Benchmark forward gravity schemes: the gravity field of a realistic lithosphere model WINTERC-G

Benchmark forward gravity schemes: the gravity field of a realistic lithosphere model WINTERC-G

Quantifying mantle mixing through configurational Entropy

Changes in core–mantle boundary heat flux patterns throughout the supercontinent cycle

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