Jérôme André Roland Noir

Last Name

Noir

First Name

Jérôme André Roland

ORCID

0000-0001-9977-0360

Organisational unit

03734 - Jackson, Andrew / Jackson, Andrew

Show all metadata

Search Results

Publications 1 - 10 of 19

Particle streak velocimetry using ensemble convolutional neural networks
Grayver, Alexander V.; Noir, Jérôme André Roland (2020)
Experiments in Fluids
Libration-driven inertial waves and mean zonal flows in spherical shells
Lin, Yufeng; Noir, Jérôme André Roland (2021)
Geophysical and Astrophysical Fluid Dynamics
Several planetary bodies in our solar system undergo a forced libration owing to gravitational interactions with their orbital companions, leading to complex fluid motions in their metallic liquid cores or subsurface oceans. In this study, we numerically investigate flows in longitudinally librating spherical shells. We focus on the Ekman number dependencies of several shear layers when the libration frequency is less than twice of the rotation frequency and the libration amplitude is small. Time-dependent flows mainly consist of inertial waves excited at the critical latitudes due to the Ekman pumping singularities, forming conical shear layers. In particular, previous theoretical studies have proposed different scalings for the conical shear layers spawned from the critical latitudes at the inner boundary. Our numerical results favour the velocity amplitude scaling (Formula presented.) predicted by Le Dizès & Le Bars (J. Fluid Mech. 2017, 826, 653) over the scaling (Formula presented.) initially proposed by Kerswell (J. Fluid Mech. 1995, 298, 311), though the Ekman numbers in our calculations are not sufficiently small to pin down this scaling. Non-linear interactions in the boundary layers drive a mean zonal flow with several geostrophic shears. Our numerical results show that geostrophic shears associated with the critical latitudes at the inner and outer boundaries exhibit the same scalings, i.e. an amplitude of (Formula presented.) over a width of (Formula presented.). Apart from the geostrophic shear associated with the critical latitude, our numerical results show that the reflection of inertial waves can induce a geostrophic shear with an amplitude of (Formula presented.) over a width of (Formula presented.). As the amplitude of the geostrophic shears increases as reducing the Ekman number, the geostrophic shears in the mean flows may be significant in planetary cores and subsurface oceans given small Ekman numbers of these systems.
Resonant and non-resonant flows in longitudinally and latitudinally librating spheres
Lin, Yufeng; Hollerbach, Rainer; Noir, Jérôme André Roland; et al. (2023)
Physics of Fluids
We investigate the linear response to longitudinal and latitudinal libration of a rapidly rotating fluid-filled sphere. Asymptotic methods are used to explore the structure of resonant modes in both cases, provided that the nondimensional libration frequency is in the range ω∈[0,2]. High-resolution numerics are then used to map out this entire frequency range, picking out both the resonant peaks as well as the non-resonant troughs in between. The kinetic energy is independent of the Ekman number E at the peaks and scales as E1/2 at the troughs. As the Ekman number is reduced, down to E=10−10 for longitudinal libration and E=10−9 for latitudinal libration, the frequency response also exhibits an increasingly fractal structure, with more and more peaks and troughs emerging. The spacing between peaks is seen to follow an E1/2 self-similarity factor. However, detailed examinations of some of the more prominent troughs shows that their widths follow an E∼0.23 self-similarity factor.
Experimental study of the flows in a non-axisymmetric ellipsoid under precession
Burmann, Fabian; Noir, Jérôme André Roland (2022)
Journal of Fluid Mechanics
Precession driven flows are of great interest for both, industrial and geophysical applications. While cylindrical, spherical and spheroidal geometries have been investigated in great detail, the numerically and theoretically more challenging case of a non-axisymmetric cavity has received less attention. We report experimental results on the flows in a precessing triaxial ellipsoid, with a focus on the base flow of uniform vorticity, which we show to be in good agreement with existing theoretical models. As predicted, the uniform vorticity component exhibits two branches of solutions leading to a hysteresis cycle as a function of the Poincaré number. The first branch is observed at low forcing and characterized by large amplitude of the total fluid rotation and a moderate tilt angle of the fluid rotation axis. In contrast, the second branch displays only a moderate fluid rotation and a large tilt angle of the fluid rotation axis, which tends to align with the precession axis. In addition, we observe the occurrence of parametric instabilities early in the first branch, which saturate in the second branch, where we observe the same order of the kinetic energy in the base flow and instabilities.
Length of Day Variations Explained in a Bayesian Framework
Kiani Shahvandi, Mostafa; Noir, Jérôme André Roland; Mishra, Siddhartha; et al. (2024)
Geophysical Research Letters
Length of Day (LOD) observations in the range 720 BCE to 2020—derived from lunar occultation and eclipse records—feature a secular trend and various long-period fluctuations. While recent estimates show that the secular trend is caused by the combination of lunar tidal friction and glacial isostatic adjustment, the causes of long-period fluctuations remain ambiguous. We first compute the climatic effects and show that they are anti-correlated with the observed fluctuations and their amplitude is (Formula presented.) 10 smaller. Then, we focus on core dynamics and solve for simplified equations of magnetohydrodynamics, namely tangential geostrophy, using Bayesian Physics-Informed Neural Networks (BPINNs) and independent archeomagnetic and modern geomagnetic observations. Within the observation and reconstruction uncertainty we can reconcile the LOD observations with reconstructions of BPINNs. Furthermore, we demonstrate that LOD variations reconstructed by dynamics of Magneto-Archimedes-Coriolis waves do not explain the observed fluctuations. These results have considerable implications for internal and external geodynamics.
Fast Quasi‐Geostrophic Magneto‐Coriolis Modes in the Earth's core
Gerick, Felix; Jault, Dominique; Noir, Jérôme André Roland (2021)
Geophysical Research Letters
Fast changes of Earth's magnetic field could be explained by inviscid and diffusion‐less quasi‐geostrophic (QG) Magneto‐Coriolis modes. We present a hybrid QG model with columnar flows and three‐dimensional magnetic fields and find modes with periods of a few years at parameters relevant to Earth's core. For the simple poloidal magnetic field that we consider here they show a localization of kinetic and magnetic energy in the equatorial region. This concentration of energy near the equator and the high frequency make them a plausible mechanism to explain similar features observed in recent geomagnetic field observations. Our model potentially opens a way to probe the otherwise inaccessible magnetic field structure in the Earth's outer core
Pressure torque of torsional Alfven modes acting on an ellipsoidal mantle
Gerick, Felix; Jault, Dominique; Noir, Jérôme André Roland; et al. (2020)
Geophysical Journal International
We investigate the pressure torque between the fluid core and the solid mantle arising from magnetohydrodynamic modes in a rapidly rotating planetary core. A 2-D reduced model of the core fluid dynamics is developed to account for the non-spherical core–mantle boundary. The simplification of such a quasi-geostrophic model rests on the assumption of invariance of the equatorial components of the fluid velocity along the rotation axis. We use this model to investigate and quantify the axial torques of linear modes, focusing on the torsional Alfvén modes (TM) in an ellipsoid. We verify that the periods of these modes do not depend on the rotation frequency. Furthermore, they possess angular momentum resulting in a net pressure torque acting on the mantle. This torque scales linearly with the equatorial ellipticity. We estimate that for the TM calculated here topographic coupling to the mantle is too weak to account for the variations in the Earth’s length-of-day.
Development of a new airborne geomagnetic mapping system with a field test at the Tsenkher hot springs Mongolia
Aubert, F.; Samrock, Friedemann; Kuvshinov, Alexey; et al. (2019)
Electromagnetically driven zonal flows in a rapidly rotating spherical shell
Hollerbach, Rainer; Wei, Xing; Noir, Jérôme André Roland; et al. (2013)
Journal of Fluid Mechanics
Precessing non-axisymmetric ellipsoids: bi-stability and fluid instabilities
Burmann, Fabian; Kira, Lennart; Noir, Jérôme André Roland (2024)
Journal of Fluid Mechanics
This study explores precession-driven flows in a non-axisymmetric ellipsoid spinning around its medium axis. Using an experimental approach, we focus on two aspects of the flow: the base flow of uniform vorticity and the development of fluid instabilities. In contrast to a preceding paper (J. Fluid. Mech., vol. 932, 2022, A24), where the ellipsoid rotated around its shortest axis, we do not observe bi-stability or hysteresis of the base flow, but a continuous transition from small to large differential rotation and tilt of the fluid rotation axis. We then use the model developed by Noir & Cébron (J. Fluid. Mech., vol. 737, 2013, pp. 412–439) to numerically determine regions in the parameter space of axial and equatorial deformations for which bi-stability may exist. Concerning fluid instabilities, we use three independent observations to track the onset of both boundary layer and parametric instabilities. Our results clearly show the presence of a parametric instability, yet the exact nature of the underlying mechanism (conical shear layer instability, shear instability and elliptical instability) is not unambiguously identified. A coexisting boundary layer instability, although unlikely, cannot be ruled out based on our experimental data. To make further progress on this topic, a new generation of experiments at significantly lower Ekman numbers (ratio of rotation and viscous time scales) is clearly needed.

Publications 1 - 10 of 19

Jérôme André Roland Noir

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results