Magnetic field models - last update: 11 May 1998, 1840 UT (RR)
The magnetic field of the Earth has been investigated by satellites for several decades now, and enough of it is known to model its average strength and shape during different levels of overall magnetic activity. Presently the most used empirical global magnetic field models are the Tsyganenko models (1987, 1989), referred to as T87 and T89, respectively, although even these consist of several submodels. Later models include T95 and T96_01 (Tsyganenko, 1995; Tsyganenko and Stern, 1996). All the realistic models start from the official International Geomagnetic Reference Field (IGRF) model, which is improved by adding magnetospheric current systems that modify it towards the true, observed configuration. Zhou et al. (1997) recently tested the T96_01 version, and found major discrepancies with the observed field only close to the cusp. Other models include Olson and Pfitzer (1974), Mead and Fairfield (1975), Alexeev et al. (1996), and Ostapenko and Maltsev (1997).

One useful application of a magnetic field model is that you can trace a field line from a given point, creating thus a map of the Earth's magnetosphere. In the series of figures below, the magnetospheric topology is seen to be dependent on the season. The model used is the T89c, and the Kp index is taken to be 2.

Earth's magnetic field from T89c model during Kp=2 for different seasons.

The problem with this kind of global models is that they work poorly for specific event studies. Because of this, local magnetic field models have been created using simultaneous magnetic observations from a number of spacecrafts (Sergeev et al., 1990; Pulkkinen et al., 1991, 1992).

Still another way to model the true magnetic field configuration is to probe magnetic field gradients via the remote sensing of the magnetic field by low-altitude spacecraft, as has been done using the isotropic boundary algorithm (Sergeev and Malkov, 1988; Sergeev et al., 1993).


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