A comprehensive model of the quiet-time, near-Earth magnetic field: phase 3

Abstract

Summary The near‐Earth magnetic field is caused by sources in the Earth's core, ionosphere, magnetosphere, lithosphere and from coupling currents between the ionosphere and the magnetosphere, and between hemispheres. Traditionally, the main field (low degree internal field) and magnetospheric field have been modelled simultaneously, with fields from other sources being modelled separately. Such a scheme, however, can introduce spurious features, especially when the spatial and temporal scales of the fields overlap. A new model, designated CM3 (Comprehensive Model: phase 3), is the third in a series of efforts to coestimate fields from all of these sources. This model has been derived from quiet‐time Magsat and POGO satellite and observatory hourly means measurements for the period 1960–1985. It represents a significant advance in the treatment of the aforementioned field sources over previous attempts, and includes an accounting for main field influences on the magnetosphere, main field and solar activity influences on the ionosphere, seasonal influences on the coupling currents, a priori characterization of the influence of the ionosphere and the magnetosphere on Earth‐induced fields, and an explicit parametrization and estimation of the lithospheric field. The result is a model that describes well the 591 432 data with 16 594 parameters, implying a data‐to‐parameter ratio of 36, which is larger than several popular field models.

Toward a better representation of the secular variation. Case study: The European network of geomagnetic observatories

“…10 differences between the model main field time series and filtered time series with an 11-year running window are shown for European observatories locations in case of horizontal component, for three main field models spanning long time intervals in the 20th century: gufm1 (Jackson et al, 2000(Jackson et al, , 1590(Jackson et al, -1990, IGRF-11 (Finlay et al, 2010(Finlay et al, , 1900(Finlay et al, -2010, and CM4 (Sabaka et al, 2004(Sabaka et al, , 1960(Sabaka et al, -2002. In case of IGRF the external signal leaked into the model is distorted by the 5 years sampling of the field, characteristic to this model.…”

“…Individually modeling the three terms related to external variations, attempted in the comprehensive modeling (Sabaka et al, 2002(Sabaka et al, , 2004, is only partially successful up to now, in spite of the significant progress compared to other types of modeling: the solar-cycle-related external term is modeled by means of D st and F 10.7 only, the electromagnetic crust and mantle response is built on a 1D radial distribution of conductivity, deduced (Olsen, 1998) from European data, and the crust response by magnetic induction is completely ignored.…”

The magnetic field changing over the southern African continent: a unique behaviour

“…Considering the CM4 model (1960 to 2002) published by Sabaka et al (2002) and a 20-year time span (to keep the same time interval as in Figure 2), the total flux for the epochs 1980 and 2000 was computed. Figure 9 shows that 20 years is enough to change the flux patterns.…”

Axial poloidal electromagnetic core-mantle coupling torque: A re-examination for different conductivity and satellite supported geomagnetic field models

“…Both field models are based on different modelling approaches. The CM4 model uses a comprehensive approach (e. g. Sabaka et al,2002;, where the magnetic field is parametrized using satellite and observational data for separate spheres, i.e. crust, ionosphere and the internal (residual) field.…”