Journal
GEOPHYSICAL JOURNAL INTERNATIONAL
Volume 179, Issue 3, Pages 1477-1487Publisher
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-246X.2009.04386.x
Keywords
Magnetic anomalies: modelling and interpretation; Rapid time variations; Satellite magnetics; Core, outer core and inner core
Categories
Funding
- Danish Government
- NASA
- ESA
- CNES
- DARA
- German Aerospace Center (DLR)
- Federal Ministry of Education and Research
- Natural Environment Research Council [NER/O/S/2003/00674] Funding Source: researchfish
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We have derived a model of the near-Earth's magnetic field using more than 10 yr of high-precision geomagnetic measurements from the three satellites Orsted, CHAMP and SAC-C. This model is an update of the two previous models, CHAOS (Olsen et al. 2006) and xCHAOS (Olsen & Mandea 2008). Data selection and model parameterization follow closely those chosen for deriving these models. The main difference concerns the maximum spherical harmonic degree of the static field (n = 60 compared to n = 50 for CHAOS and xCHAOS), and of the core field time changes, for which spherical harmonic expansion coefficients up to n = 20 are described by order 5 splines (with 6-month knot spacing) spanning the years from 1997.0 to 2009.5. Compared to its predecessors, the temporal regularization of the CHAOS-2 model is also modified. Indeed, second and higher order time derivatives of the core field are damped by minimizing the second time derivative of the squared magnetic field intensity at the core-mantle boundary. The CHAOS-2 model describes rapid time changes, as monitored by the ground magnetic observatories, much better than its predecessors.
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