Long-term changes of Earth’s internal magnetic field and their effects on the shielding and cosmogenic nuclides

The Earth’s magnetic field shields our planet against highly energetic particles from the Sun and outer space. Over geological times, the time-varying geomagnetic field exhibited periods of dramatic changes, both in intensity and direction. Recent data compilations of paleomagnetic records enable us to model the long-term, global evolution of the geomagnetic field and better understand the internal dynamics and underlying phenomena. On the other hand, the spatial and temporal changes influence the shielding and cosmogenic nuclide production rates. In general, the higher the field intensity, the larger the shielding and the fewer cosmogenic nuclides are produced in the atmosphere.

We cover the evolution of the geomagnetic field over the past 100 000 years by presenting characteristics found to be robust in available global models. The period includes a few geomagnetic excursions, including the Laschamps excursion 41 000 years ago – when the intensity was globally very low, and the field had a complex, multipolar structure. Several properties of and estimates based on the models will be discussed, including the field morphology at the core-mantle boundary and Earth’s surface, global cutoff rigidity variations, impact area, global cosmic ray flux, and production rates of different cosmogenic nuclides. The latter results from the models are validated through comparison with actual measurements from ice and marine cores.