Strength of the magnetic field at Earth’s surface

Our magnetic field is thought to be produced largely by an ocean of superheated, swirling liquid iron that makes up the outer core 3000 km under our feet. Acting like the spinning conductor in a bicycle dynamo, it generates electrical currents and thus the continuously changing electromagnetic field. Other sources of magnetism are the minerals in Earth’s mantle and crust, while the ionosphere and the magnetosphere also play a role. Since salt water is conductive, oceans make an additional, albeit weak, contribution to the magnetic field. The image shows how the strength of the magnetic field varies at Earth’s surface. By analysing the different characteristics of the observed field, ESA’s Swarm mission is leading to new insights into many natural processes, from those occurring deep inside the planet to weather in space caused by solar activity.