@article{AsariWardinski2015,
  author    = {Asari, Seiki and Wardinski, Ingo},
  title     = {On magnetic estimation of Earth's core angular momentum variation},
  series = {Journal of geophysical research : Solid earth},
  volume    = {120},
  journal   = {Journal of geophysical research : Solid earth},
  number    = {10},
  publisher = {American Geophysical Union},
  address   = {Washington},
  issn      = {2169-9313},
  doi       = {10.1002/2014JB011458},
  pages     = {6740 -- 6757},
  year      = {2015},
  abstract  = {We study systematically the estimation of Earth's core angular momentum (CAM) variation between 1962.0 and 2008.0 by using core surface flow models derived from the recent geomagnetic field model C(3)FM2. Various flow models are derived by changing four parameters that control the least squares flow inversion. The parameters include the spherical harmonic (SH) truncation degree of the flow models and two Lagrange multipliers that control the weights of two additional constraints. The first constraint forces the energy spectrum of the flow solution to follow a power law l-p, where l is the SH degree and p is the fourth parameter. The second allows to modulate the solution continuously between the dynamical states of tangential geostrophy (TG) and tangential magnetostrophy (TM). The calculated CAM variations are examined in reference to two features of the observed length-of-day (LOD) variation, namely, its secular trend and 6year oscillation. We find flow models in either TG or TM state for which the estimated CAM trends agree with the LOD trend. It is necessary for TM models to have their flows dominate at planetary scales, whereas TG models should not be of this scale; otherwise, their CAM trends are too steep. These two distinct types of flow model appear to correspond to the separate regimes of previous numerical dynamos that are thought to be applicable to the Earth's core. The phase of the subdecadal CAM variation is coherently determined from flow models obtained with extensively varying inversion settings. Multiple sources of model ambiguity need to be allowed for in discussing whether these phase estimates properly represent that of Earth's CAM as an origin of the observed 6year LOD oscillation.},
  language  = {en}
}
@misc{LesurWardinskiAsarietal.2010,
  author    = {Lesur, Vincent and Wardinski, Ingo and Asari, Seiki and Minchev, Borislav and Mandea, Mioara},
  title     = {Modelling the Earth's core magnetic field under flow constraints},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
  number    = {844},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-43036},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-430369},
  pages     = {503 -- 516},
  year      = {2010},
  abstract  = {Two recent magnetic field models, GRIMM and xCHAOS, describe core field accelerations with similar behavior up to Spherical Harmonic (SH) degree 5, but which differ significantly for higher degrees. These discrepancies, due to different approaches in smoothing rapid time variations of the core field, have strong implications for the interpretation of the secular variation. Furthermore, the amount of smoothing applied to the highest SH degrees is essentially the modeler's choice. We therefore investigate new ways of regularizing core magnetic field models. Here we propose to constrain field models to be consistent with the frozen flux induction equation by co-estimating a core magnetic field model and a flow model at the top of the outer core. The flow model is required to have smooth spatial and temporal behavior. The implementation of such constraints and their effects on a magnetic field model built from one year of CHAMP satellite and observatory data, are presented. In particular, it is shown that the chosen constraints are efficient and can be used to build reliable core magnetic field secular variation and acceleration model components.},
  language  = {en}
}
@article{AsariWardinski2018,
  author    = {Asari, Seiki and Wardinski, Ingo},
  title     = {Interannual fluctuations of the core angular momentum inferred from geomagnetic field models},
  series = {Magnetic Fields in the Solar System : Planets, Moons and Solar Wind Interactions},
  volume    = {448},
  journal   = {Magnetic Fields in the Solar System : Planets, Moons and Solar Wind Interactions},
  publisher = {Springer},
  address   = {Dordrecht},
  isbn      = {978-3-319-64292-5},
  issn      = {0067-0057},
  doi       = {10.1007/978-3-319-64292-5_4},
  pages     = {111 -- 123},
  year      = {2018},
  language  = {en}
}