How do electric currents in Earth’s liquid outer core generate the geomagnetic field?

The geomagnetic field is generated by the geomagnetic dynamo, a process occurring within Earth’s liquid outer core. This mechanism relies on the motion of electrically conducting fluid—specifically liquid iron—moving across an existing magnetic field to induce electric currents. These currents, in turn, produce a magnetic field that interacts with the fluid motion to amplify and sustain the field.1

This process is driven by thermal convection, where heat released by the freezing of the liquid core onto the solid inner core causes hot fluid to rise. As this fluid moves, the Coriolis force introduces twists into the motion, which are essential for the dynamo to function. Two primary effects describe how this geometry generates the field:1

• Omega Effect: Differential rotation "wraps" magnetic field lines around the rotation axis, creating a large toroidal field.1
• Alpha Effect: Rising convective cells twist these toroidal field lines, eventually reconnecting them to re-create the original poloidal field.1

This self-sustaining cycle requires the fluid to be a good conductor, the presence of an initial magnetic field, and the twisting forces provided by planetary rotation.1