Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 35, 613-628, 2017
http://www.ann-geophys.net/35/613/2017/
doi:10.5194/angeo-35-613-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Regular paper
09 May 2017
Estimating a planetary magnetic field with time-dependent global MHD simulations using an adjoint approach
Christian Nabert1, Carsten Othmer1, and Karl-Heinz Glassmeier1,2 1Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
2Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
Abstract. The interaction of the solar wind with a planetary magnetic field causes electrical currents that modify the magnetic field distribution around the planet. We present an approach to estimating the planetary magnetic field from in situ spacecraft data using a magnetohydrodynamic (MHD) simulation approach. The method is developed with respect to the upcoming BepiColombo mission to planet Mercury aimed at determining the planet's magnetic field and its interior electrical conductivity distribution. In contrast to the widely used empirical models, global MHD simulations allow the calculation of the strongly time-dependent interaction process of the solar wind with the planet. As a first approach, we use a simple MHD simulation code that includes time-dependent solar wind and magnetic field parameters. The planetary parameters are estimated by minimizing the misfit of spacecraft data and simulation results with a gradient-based optimization. As the calculation of gradients with respect to many parameters is usually very time-consuming, we investigate the application of an adjoint MHD model. This adjoint MHD model is generated by an automatic differentiation tool to compute the gradients efficiently. The computational cost for determining the gradient with an adjoint approach is nearly independent of the number of parameters. Our method is validated by application to THEMIS (Time History of Events and Macroscale Interactions during Substorms) magnetosheath data to estimate Earth's dipole moment.

Citation: Nabert, C., Othmer, C., and Glassmeier, K.-H.: Estimating a planetary magnetic field with time-dependent global MHD simulations using an adjoint approach, Ann. Geophys., 35, 613-628, doi:10.5194/angeo-35-613-2017, 2017.
Publications Copernicus
Short summary
The interaction of the solar wind with a planetary magnetic field causes electrical currents that modify the magnetic field distribution around the planet. We present an approach to estimating the planetary magnetic field contribution by minimizing the misfit between simulation results and in situ spacecraft data. The approach is developed with respect to the upcoming BepiColombo mission to Mercury aimed at determining the planet's magnetic field.
The interaction of the solar wind with a planetary magnetic field causes electrical currents...
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