Why all the effort?

Direct measurements of the Earth's magnetic field are continuously made around the world at magnetic observatories, and are obtained at all kinds of exotic locations from various oceanographic, land, aircraft and even satellite surveys. All this activity has made some people to wonder "why all the effort?". There are two obvious reasons that stand out for me. In the study of the Earth's history, very few physical quantities have left any record that can be measured today. The study of seismology and the Earth's gravity field have revealed many secrets about the Earth's interior, but there is no timeline in which to examine how these measurements may have, or are, changing with time. Measurements that can be examined retroactively are extremely important to make inferences about what the Earth may have been like in the past. When measuring the magnetic field, what it is actually determined is a combination of fields produced by different sources. The main Earth's magnetic field is generated in the fluid outer core by a self-exciting dynamo process. In addition to sources in the outer core the magnetic field observable at the Earth's surface has sources in the crust, and in the ionosphere and magnetosphere. The geomagnetic field varies on a range of scales and a description of these variations is now provided, from low frequency to high frequency variations, in both the space and time domains. Earth's magnetic field is very dynamic, and the effects of these dynamics on short-time scales (linked to Sun's activity) can be seen on the ground, as they affect power grids and electronics, causing blackouts and interference with radios and telephones.

Measuring, mapping and understanding these different aspects of the Earth's magnetic field, was and is my own contribution to a large international effort on this topic. In what follows, I will provide a more detailed account of a few aspects of my work, to show how the Earth's magnetic field can be both a tool and a hazard to modern world, and why I'm interested in some other planetary magnetic fields such as Mars, Mercury or Venus. Of course, my publications list provides further details about my research area.

Ancient magnetic data

Magnetic observations prior to the establishment of observatories and an absolute method of measuring magnetic intensity by Gauss in the 1830s were made, amongst others, by mariners engaged in merchant and naval shipping. These are mainly of declination and extend the global historic data-set back to the beginning of the 16th century. In the course of these studies we discovered some new sources of magnetic data, and also prior attempts to describe the Earth's magnetic field (Nautonier's book, 1602). This part of my work brought to my attention old books and maps originating from the French Navy old measurements and old instruments, and maybe the first geomagnetic map. Moreover, in some other studies, an overview of the magnetic field variations in Western Europe, over the last centuries is given, with a sustainable work on data from Paris, London, Munich and Bucharest.

Observatories

Other ground direct observations

Satellites