IsTerre candidate to the International Geomagnetic Reference Field model

2019, 4 à 6 mois
Laboratoire(s) de rattachement : ISTerre
Encadrant(s) : Nicolas Gillet
Co-encadrant(s) : Loic Huder
Contact(s) : nicolas.gillet
Lieu : Grenoble
Niveau de formation & prérequis : Master in physics, geophysics or applied maths
Mots clés : geomagnetism, satellite observations, inverse problem

Every 5 years, several institutes of geosciences over the world propose candidate models to be used for the construction of the International Geomagnetic Reference Field (IGRF) model [1]. This interpolation of geomagnetic measurement is fundamental for numerous academic and industrial applications, from space weather to orientation. The aim of the project is to build IsTerre’s next candidate model, extending over the period 2015-2020 our previous proposition, named « COV-OBS » [2]. The specificity of the COV-OBS model is to combine information obtained from
(i) magnetic observations at different locations (including continuous satellite data over the past 18 yrs, observatory series since 1840, surveys, etc.), and
(ii) a priori knowledge about the temporal spectrum of ground-based records, well expressed in a stochastic framework.
As such, COV-OBS is the only available continuous model covering the entire observatory and satellite eras. The stochastic framework furthermore allows to derive realistic model uncertainties, of primary importance if one aims at using such model in geomagnetic data assimilation algorithms [3].
We plan here to include several novelties when constructing this revised model, such as accounting for satellite data from the Swarm and Champ missions by means of virtual observatory series [4], or extending the model back in time using historical records prior to 1840 (the advent of absolute magnetic intensity measurements).
The student will have to run and adapt a code for inverting geomagnetic data. He/she should be comfortable with applied mathematics.

[1] Thébault, et al. "International geomagnetic reference field : the 12th generation." Earth, Planets and Space 67.1 (2015) : 79.
[2] Gillet, Barrois, and Finlay. "Stochastic forecasting of the geomagnetic field from the COV-OBS. x1 geomagnetic field model, and candidate models for IGRF-12." Earth, Planets and Space 67.1 (2015) : 71.
[3] Fournier, et al. "An introduction to data assimilation and predictability in geomagnetism." Space science reviews 155.1-4 (2010) : 247-291.
[4] Barrois, et al. "Assimilation of ground and satellite magnetic measurements : inference of core surface magnetic and velocity field changes." Geophys. J. Int. 215.1 (2018) : 695-712.