Julien Aubert, CNRS, IPG Paris

I am a CNRS senior researcher working at the Institut de Physique du Globe de Paris (IPGP), within the Geological Fluid Dynamics team. 


I am interested in the interpretation of the geomagnetic signal emanating from Earth’s liquid outer core. Over a broad range of space and time scales, this signal is a powerful probe for investigating the structure, dynamics and geological history of our planet. Understanding the geodynamo is an outstanding fundamental challenge of Physical Sciences as well as Earth Sciences. 


To this end I develop and use direct numerical computer simulations of the dynamo process, as well as data assimilation algorithms aiming at forecasting the future evolution of the geomagnetic field. This has important societal impacts as the geomagnetic field interacts with life on Earth and with human technological activities.

what (according to my computer) lies beneath our feet

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A new reversal mechanism for the geodynamo

06/05/2025

The successful numerical simulation of geomagnetic reversals in the mid 90’s has crucially contributed to the development and popularity of Earth’s core dynamics as a scientific discipline. However, some key difficulties concerning the applicability of numerical results to Earth’s core conditions have remained unsolved since 30 years. In a new paper published in Physics of the Earth and Planetary Interiors, we present a solution to some (but not all) of these problems. The new reversal mechanism that we propose indeed demonstrably applies to the physical conditions of Earth’s core. A puzzling result is that it predicts that a faster cooling of Earth’s core will cause less frequent geomagnetic reversals, whereas previous mechanisms predicted the opposite. This opens interesting prospects for the reanalysis of the reversal records in connection with records of the deep Earth geodynamics.


Note: the copyediting job done by Elsevier on this paper is poor. Some mistakes have been introduced on their side, even after proof stage, such that I cannot recommend their pdf for reference. Please use the one below, from arXiv or from HAL.


Aubert, J., Landeau, M., Fournier, A., Gastine, T.: Core-surface kinematic control of polarity reversals in advanced geodynamo simulations, Phys. Earth. Planet. Int., 2025, doi: 10.1016/j.pepi.2025.107365

Rapid geomagnetic variations as evidence for Earth's fully convective core

12/03/2025

In a new paper published in Physics of the Earth and Planetary Interiors, I present the first self-consistent simulations performed at the physical conditions of Earth’s core of a stably stratified top layer in interplay with the underlying convection and dynamo action. I show that the interannual to decadal geomagnetic variations observed by geomagnetic satellites are largely incompatible with strong stratification and favour the hypothesis of a fully convective core. 


Aubert, J.: Rapid geomagnetic variations and stable stratification at the top of Earth’s core, Phys. Earth. Planet. Int., 2025, doi: 10.1016/j.pepi.2025.107335

Numerical geodynamo simulation reaches the physical conditions of Earth's core

07/06/2023

In a new paper published in Geophysical Journal International, I present the first numerical geodynamo simulations that operate at the physical conditions of Earth’s core. Such simulations have been enabled by terminating the exploration of the theoretical parameter space ‘path’ that we designed in 2017. Here the simulations are furthermore constrained with the available geomagnetic data from the past 180 years by a data assimilation approach. This results in model trajectories that are both morphologically and dynamically relevant, and reproduce the details of observed geomagnetic variations over time scales of years to centuries. An interesting perspective of this work is the possibility to extract significantly more geophysical information on the structure and history of the Earth from the geomagnetic signal than was previously possible. 


Aubert, J.: State and evolution of the geodynamo from numerical models reaching the physical conditions of Earth’s core, Geophys. J. Int. 235, 468-487, 2023, doi: 10.1093/gji/ggad229