On the Earth's magnetospheric dynamics: Nonequilibrium evolution and the fluctuation theorem

The Earth's magnetosphere evolves as an out‐of‐equilibrium system due to the continuous coupling with the solar wind and the Earth's ionosphere. We test the validity of the symmetries implied in the Fluctuation Theorem for the magnetospheric dynamics by investigating the long‐term evolution of the Earth's magnetospheric ring current, as monitored by the geomagnetic Dst index. We find that the symmetries implied by the Fluctuation Theorem are all verified, thus providing a proof of the existence of a steady state far from equilibrium for the Earth's magnetosphere. A possible link between the Dst index and the entropy production rate is also proposed and discussed.