Magnetic Reconnection

When two magnetic fields pointing opposite ways press together, they can break and re-link explosively — like rubber bands snapping into a new arrangement. This is how solar wind energy gets inside Earth's magnetic bubble.

Reconnection changes magnetic topology in thin current sheets, converting field energy to plasma kinetic and thermal energy. It powers flares and CMEs at the Sun, dayside solar wind entry when Bz is southward, and the tail collapse that triggers substorms.

Reconnection is why Bz matters: southward Bz enables dayside reconnection, opening the energy tap that ultimately lights the aurora.