Working on understanding the physics of how an electron oscillates along the Earth's magnetic field. I understand that an electron will spiral around the magnetic field line, that's easy to tell from the Lorentz force. What I don't understand is what causes the oscillation. My best guess is that, as the magnetic field lines come close together as they come close to the Earth, this simulates a changing magnetic field from the electron's view, and induces an electric field in the direction that would dampen the electron's motion and reverse it. What's giving me a hard time is understanding specifically how an electric field is created in that direction. Any insight or tips?