The Earth’s Magnetic Field at the CHAMP Satellite Epoch

Since the Carl-Friedrich Gauss epoch, the Earth’s magnetic field has changed dramatically, its dipole moment decreasing by some 10%. This single observation has raised a large number of questions about a future possible polarity transition, and consequently the possible effects on the Earth’s environment. Here, the progress made over the last few years, when the advent of the satellite era brought a major breakthrough in our understanding of the geomagnetic field at large scales, is summarized. Obtaining good data from observations is a prerequisite, so ground-based and satellite measurements are described. By properly combining these data, information about the characteristics of the geomagnetic field can be retrieved. So, recent global geomagnetic field models based on spherical harmonic analyses are generally discussed. The GRIMM model, as a powerful tool to study the internal geomagnetic field, is discussed in more details. An important and ongoing topic is also the description of the lithospheric contributions, so a large part of this chapter is dedicated to the large and small scales of this field. An outlook to expected future results and unresolved questions is provided in the final part of this chapter.