TU Braunschweig: Geomagnetic Variations
Earth´s magnetic field has been in existence since the early history of our planet, and it is known to be caused by dynamo action in the liquid outer core. Due to the instability of this process, reversals of the predominant dipolar component, as well as relatively short periods of very weak total fields occur at irregular intervals. Currently the geomagnetic field strength decreases quite rapidly. The dipolar part has dropped by 10 % within the past 300 years. In the northern atlantic region the present rate of decrease is 100 nT/year, that is, 25 % per century. Such rapidly declining field strength may be interpreted as an indication for a forthcoming field reversal, or for a relatively large recent field. Since the magnetic field jointly with the atmosphere shields Earth´s surface against incident high-energy cosmic rays, it is crucial to investigate the spatial structure and the temporal evolution of field reversals, as well as details of geomagnetic variations, their causes and effects on Earth´s atmosphere.
This programme aims at a more complete understanding of the spatio-temporal structure of geomagnetic variations in general, and of field reversal periods in particular. Furthermore, associated geodynamical processes will be investigated by means of numerical modelling and observations in order to identify the key mechanisms that cause geomagnetic variations, and potential effects on the system Earth will be studied.
The Priority Programme presented here is supposed to comprise experimental, theoretical, and numerical efforts to investigate five key subjects:
- investigation of present secular variations of Earth´s magnetic field by means of measurements of the German small satellite CHAMP, and their relation to the distribution of electrical conductivity in Earth´s mantle,
- high-resolution paleomagnetic investigations at sediments and volcanic rocks before, during, and after field reversal periods to yield synchronous and global surveys of variations of the paleomagnetic field,
- investigations of the processes leading to remanent magnetization in sediments in order to separate paleoclimatic, paleoecological, and paleomagnetic effects,
- theoretical studies and numerical simulations of geodynamo action to yield a more comprehensive understanding of the reversal phenomenon, which is crucial for a meaningful interpretation of the observed spatio-temporal structure of the paleomagnetic field and the recent field,
- investigation of the influence of magnetic field topology changes during field reversals on the incident high-energy particle flux, and of potential effects on the upper atmosphere.
Although our understanding of the geodynamo has improved considerably over the recent years, it is still rather incomplete in many respects. A major goal of this Priority Programme is thus the identification of dynamo models which comprise major observed properties of Earth´s magnetic field and the full spectrum of its spatial and temporal variations, in order to answer the question whether the geodynamo is currently approaching a field reversal period.
The scientific activities to reach such a goal require an interdisciplinary basis consisting of contributors from the fields of geophysics, geology, geodesy, geochemistry, solar physics, atmospheric physics, paleoclimatology, and paleooceanography. The degree of coordination provided by a Priority Programme makes such a cooperation and the close association of those different disciplines possible.