Proposed realisations

• First step (1998 - 1999):

  We want to share our experience by summarizing the latest results on the different subjects related to the Earth core and rotation and by putting that on the web. We are making a bibliography of existing publications on that subject. As the determination of core angular momentum is highly dependent on the approximations used in the computations (geostrophic, frozen-flux, etc.), we have given on our web site a description of the theory behind and the relevant information necessary to understand the data. The subjects treated are: core convection, core modes, core flow, core composition, geomagnetism, CMB torques, inner core differential rotation and Earth's rotation changes due to the core. We have additionally made the link between existing bodies related to the core and the IERS community. We think that this first step will improve our knowledge and will help the IERS community to understand core-related phenomena of interest for IERS.

• Second step (1999-present):

  We make available to the scientific community all the relevant data for studies of core-mantle angular momentum.

  1. CMB topography derived from seismology or from steady-state convection computations
  2. core flows and angular momentum derived from computations constrained by the observed surface magnetic field and its secular variation
  3. core flows and angular momentum as derived from lod data
  4. core flows and angular momentum as derived from both lod and surface magnetic data
  5. core flows and angular momentum from the study of core dynamics
  6. core flows and angular momentum variations of the inner core and the solid mantle from geodynamo simulations
  We share our experience on modeling the core and its effects on the Earth rotation parameters, and archive different already existing models. At this point, the following remark is essential. Because there are no direct observations of the core flows to lead to well-constrained models as exist for the ocean and atmosphere, only indirect calculations of core angular momentum can be obtained from core flows derived from variations in the poloidal magnetic field observed at the surface. Further, these flows depend on poorly constrained additional assumptions to resolve formal non-uniqueness in the solution. Consequently, it is very speculative to give the associated changes of the Earth's angular momentum without any other constraint. Nevertheless, the Earth's rotation variations being well correlated with the magnetic field at decadal time scale, data of variations of the lod can be used to constrain the core angular momentum.

• Third step (2001-present):

  We plan to validate the models presented in the second step by using the IERS observed EOP, and to share the information with the IERS community (this web service, to be built later). This step would be separated into short period and long period time scales. For the long period time scale, observed variation of the length-of-day will be used in the validation process; on short time scale, the information from the effect of the free nutations (Free Core Nutation (FCN) and Free Inner Core Nutation (FICN)) on nutation and diurnal polar motion, as well as the information from the resonance induced in the tidal forced nutations will be used.

• Fourth step (future):

  When one model will be validated and experienced on data, we plan to make it available, understandable and runnable on data (software should be provided) to the IERS community (future web service).

• Remark :

  When models are run, when information are used, or when data are treated, it is expected and encouraged that the IERS scientific community interacts for an exchange of ideas and opinions, in particular, for a better understanding of the physics inside the different parts of the models (or of the potentially missing parts). Please send us an e-mail for providing us with your suggestions.