Journal article
The CHAOS-4 geomagnetic field model
National Space Institute, Technical University of Denmark1
Geomagnetism, National Space Institute, Technical University of Denmark2
Helmholtz Centre Potsdam - German Research Centre for Geosciences3
NASA Goddard Space Flight Center4
IT-Department, National Space Institute, Technical University of Denmark5
We present CHAOS-4, a new version in the CHAOS model series, which aims to describe the Earth's magnetic field with high spatial and temporal resolution. Terms up to spherical degree of at least n = 85 for the lithospheric field, and up to n = 16 for the time-varying core field are robustly determined.
More than 14 yr of data from the satellites Ørsted, CHAMP and SAC-C, augmented with magnetic observatory monthly mean values have been used for this model. Maximum spherical harmonic degree of the static (lithospheric) field is n = 100. The core field is expressed by spherical harmonic expansion coefficients up to n = 20; its time-evolution is described by order six splines, with 6-month knot spacing, spanning the time interval 1997.0-2013.5.
The third time derivative of the squared radial magnetic field component is regularized at the core-mantle boundary. No spatial regularization is applied to the core field, but the high-degree lithospheric field is regularized for n > 85. CHAOS-4 model is derived by merging two submodels: its low-degree part has been derived using similar model parametrization and data sets as used for previous CHAOS models (but of course including more recent data), while its high-degree lithospheric field part is solely determined from low-altitude CHAMP satellite observations taken during the last 2 yr (2008 September-2010 September) of the mission.
We obtain a good agreement with other recent lithospheric field models like MF7 for degrees up to n = 85, confirming that lithospheric field structures down to a horizontal wavelength of 500 km are currently robustly determined.
Language: | English |
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Year: | 2014 |
Pages: | 815-827 |
ISSN: | 1365246x and 0956540x |
Types: | Journal article |
DOI: | 10.1093/gji/ggu033 |
ORCIDs: | Olsen, Nils , Finlay, Chris and Tøffner-Clausen, Lars |