This is the trigger. Without it, nothing happens.
The Bz shows whether the solar wind is repelled or absorbed by Earth's magnetic field. If Bz is positive (northward), the aurora stays off. Only a sharp negative Bz (southward) opens the door for particles to pour in and ignite the sky.
Our Expert Edge: We track Bz in nanoTeslas from the DSCOVR satellite in real time. We don't move unless we see a sustained negative trend. When Bz drops to -5 nT or lower, we guarantee dynamic, dancing lights — not faint smudges.