Philippe David Marti

Last Name

Marti

First Name

Philippe David

ORCID

0000-0002-3936-1503

Organisational unit

03734 - Jackson, Andrew / Jackson, Andrew

Show all metadata

Search Results

Publications 1 - 10 of 12

The effects of Ekman pumping on quasi-geostrophic Rayleigh–Bénard convection
Plumley, Meredith; Julien, Keith; Marti, Philippe David; et al. (2016)
Journal of Fluid Mechanics
Waves in the Earth's core. IV. The structure of inviscid torsional oscillations in a spherical shell
Yuan, Longhui; Marti, Philippe David; Luo, Jiawen; et al. (2025)
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
We study the properties of cylindrical oscillations of electrically conducting fluid in the presence of a magnetic field, a phenomenon known in geomagnetism as torsional oscillations (TOs) since their discovery by J. B. Taylor and S. I. Braginsky. The chosen geometry is a spherical shell, consistent with Earth's present-day geometry. We concentrate on the scenario where fluid viscosity is absent in our calculations, but magnetic diffusivity is retained, appropriate to the geophysical conditions in Earth's fluid outer core. Two axisymmetric background magnetic fields that provide the restoring torques to the motions are considered, one of dipole parity and the other of quadrupole parity. The anticipated class of equatorially symmetric (ES) azimuthal motions is joined by an antisymmetric class that exists in the shell geometry but is absent in the full sphere. Compared to previous studies in a full sphere, our results reveal that computing the eigenmodes of TOs in a spherical shell under the inviscid limit is considerably more computationally challenging. Only one large-scale eigenmode exists (filling the whole shell), while many modes with higher frequencies tend to be concentrated inside the tangent cylinder. We complement our inviscid calculations with calculations in which viscosity is retained, and find convergence (with decreasing viscous diffusion) towards the inviscid results.
Thermal convection in the internally heated sphere
Sternberg, Tobias; Marti, Philippe David; Jackson, Andrew (2025)
Journal of Fluid Mechanics
Waves in the Earth's core. II. Magneto–Coriolis modes
Luo, Jiawen; Marti, Philippe David; Jackson, Andrew (2022)
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
Magnetic quenching of the inverse cascade in rapidly rotating convective turbulence
Maffei, Stefano; Calkins, Michael A.; Julien, Keith; et al. (2019)
Physical Review Fluids
Accurate and efficient Jones-Worland spectral transforms for planetary applications
Marti, Philippe David; Jackson, Andrew (2021)
PASC '21: Proceedings of the Platform for Advanced Scientific Computing Conference
Spectral transforms between physical space and spectral space are needed for fluid dynamical calculations in the whole sphere, representative of a planetary core. In order to construct a representation that is everywhere smooth, regular and differentiable, special polynomials called Jones-Worland polynomials, based on a type of Jacobi polynomial, are used for the radial expansion, coupled to spherical harmonics in angular variables. We present an exact, efficient transform that is partly based on the FFT and which remains accurate in finite precision. Application is to high-resolution solutions of the Navier-Stokes equation, possibly coupled to the heat transfer and induction equations. Expected implementations would be in simulations with P3 degrees of freedom, where P may be greater than 103. Memory use remains modest at high spatial resolution, indeed typically P times lower than competing algorithms based on quadrature.
The ICON-A model for direct QBO simulations on GPUs (version icon-cscs:baf28a514)
Giorgetta, Marco A.; Sawyer, William; Lapillonne, Xavier; et al. (2022)
Geoscientific Model Development
Classical numerical models for the global atmosphere, as used for numerical weather forecasting or climate research, have been developed for conventional central processing unit (CPU) architectures. This hinders the employment of such models on current top-performing supercomputers, which achieve their computing power with hybrid architectures, mostly using graphics processing units (GPUs). Thus also scientific applications of such models are restricted to the lesser computer power of CPUs. Here we present the development of a GPU-enabled version of the ICON atmosphere model (ICON-A), motivated by a research project on the quasi-biennial oscillation (QBO), a global-scale wind oscillation in the equatorial stratosphere that depends on a broad spectrum of atmospheric waves, which originates from tropical deep convection. Resolving the relevant scales, from a few kilometers to the size of the globe, is a formidable computational problem, which can only be realized now on top-performing supercomputers. This motivated porting ICON-A, in the specific configuration needed for the research project, in a first step to the GPU architecture of the Piz Daint computer at the Swiss National Supercomputing Centre and in a second step to the JUWELS Booster computer at the Forschungszentrum Julich. On Piz Daint, the ported code achieves a single-node GPU vs. CPU speedup factor of 6.4 and allows for global experiments at a horizontal resolution of 5 km on 1024 computing nodes with 1 GPU per node with a turnover of 48 simulated days per day. On JUWELS Booster, the more modern hardware in combination with an upgraded code base allows for simulations at the same resolution on 128 computing nodes with 4 GPUs per node and a turnover of 133 simulated days per day. Additionally, the code still remains functional on CPUs, as is demonstrated by additional experiments on the Levante compute system at the German Climate Computing Center. While the application shows good weak scaling over the tested 16-fold increase in grid size and node count, making also higher resolved global simulations possible, the strong scaling on GPUs is relatively poor, which limits the options to increase turnover with more nodes. Initial experiments demonstrate that the ICON-A model can simulate downward-propagating QBO jets, which are driven by wave-mean flow interaction.
Heat transfer and flow regimes in quasi-static magnetoconvection with a vertical magnetic field
Yan, Ming; Calkins, Michael A.; Maffei, Stefano; et al. (2019)
Journal of Fluid Mechanics
Rotating thermal convection in a full sphere with heterogeneous temperature boundary conditions
Zhang, Yutong; Jackson, Andrew; Marti, Philippe David; et al. (2025)
Geophysical Journal International
The large-scale thermal inhomogeneity at the Earth's core mantle boundary generates lateral thermal winds, which can penetrate the core's interior due to the Coriolis force, and interact with the convecting flow. This boundary driving may provide an additional mechanism for convection in the liquid core, aside from the secular cooling, prior to the nucleation of the inner core. To understand the combined effects of boundary driving and secular cooling on the hydrodynamic process of the core without an inner boundary, we perform direct numerical simulations of a Boussinesq fluid in a rotating and internally heated full sphere. The boundary of the sphere is stress-free, with a fixed-temperature boundary condition imposed proportional to the $Y_{mm}$ spherical harmonic function ($m=1,2,3$), and an inhomogeneity parameter $\epsilon$ quantifying the relative magnitude of the boundary inhomogeneity. At Prandtl number of 1 and Ekman number of $3\times 10<^>{-4}$, the diagnostics, time-dependence and field morphology of the flow are investigated for a range of inhomogeneity parameters $0.02\le \epsilon \le 0.50$ and Rayleigh numbers $0.1\le \mathrm{ Ra}/\mathrm{ Ra}_\mathrm{ c}\le 1.9$, where $\mathrm{ Ra}_\mathrm{ c}$ is the critical Rayleigh number for convection in the homogeneous boundary case. Focusing on the $Y_{22}$ boundary conditions, we find the existence of four distinct flow regimes, that exhibit different flow morphologies. We further differentiate between them through the differences exhibited in the heat transport and dissipation rate as functions of $\mathrm{ Ra}$ and $\epsilon$. In particular, it is observed that the viscous and thermal dissipation of the flow varies as $\epsilon <^>2$, in the range investigated.
Invariance of dynamo action in an early-Earth model
Lin, Yufeng; Marti, Philippe David; Jackson, Andrew (2025)
Nature
Magnetic field generation on Earth has probably persisted for at least 3.5 Gyr (refs. 1,2), initially sustained by secular cooling of the Earth’s core and, more recently, by the growth of the solid inner core3. Numerical models of the present-day geodynamo have proved to be successful in producing Earth-like magnetic fields4, 5, 6-7 and approaching realistic dynamic regimes8, 9, 10-11. However, thermal evolution12,13 and palaeomagnetic records14,15 suggest that the geodynamo operated for most of geomagnetic history without a solid inner core. Dynamo action in a whole fluid core remains poorly understood. Here we show dynamo actions that are independent of fluid viscosity in the correct geometry of the Earth’s core in the deep past at extremely low viscosity, demonstrating the negligible role of fluid viscosity in our dynamo simulations. Our early-Earth geometry models produce magnetic field intensity and morphologies that are compatible with the palaeomagnetic data in the deep past while showing remarkable similarity to the present-day magnetic field. This raises questions about the role of the solid inner core in producing the spatial-temporal variations of the observed Earth’s magnetic field7,16, 17-18.

Publications 1 - 10 of 12

Philippe David Marti

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results