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The
rapid temporal evolution of the observed magnetic field and the
associated processes in the Earth's liquid outer core
Summary
Recent models of the Earth's magnetic field, derived from observatory
and satellite data, present rapid temporal evolutions, on sub-decadal
time-scales, that have not been seen before. These rapid evolutions are
particularly apparent in the secular acceleration, i.e. in the time
derivative of the core field secular variation. What is the origin of
this signal? How much is it distorted by the conductive mantle? What
processes in the core can give rise to these fast evolutions? To
address these questions, an
international team has been organized covering three specialties, namely:
Data analysis,Core flow modelling and Magnetohydrodynamics.
Regarding the data analysis, the repeatability of the observed
signal and its evolution in time has to be investigated. This can be
done using the most recent available satellite data, as well as older
observatory data. The impact of the conductive mantle on the observed
signal needs also to be accounted for. In the derivation of core flow
models, little attention is usually given to the temporal evolution of
these models. As the magnetic field acceleration is now better
resolved, this aspect of the core flow modelling can be also
considered. The derivation of these flow models commonly rely on the
frozen-flux approximation and quasi-geostrophy assumptions that need to
be tested. This can be done by characterizing, under these assumptions,
hydromagnetic normal modes in the core. Such modes could be responsible
for the observed fast changes in both the field and the flow.
Two short workshops are planned by the team to organize
collaboration, build a common research strategy and exchange
information. Hopefully, significant progresses will be made in
understanding these new aspects of the core field evolution.
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