How to Look for a South-pointing Magnetic Field

NASA’s ACE satellite, stationed a million miles away between the earth and the sun, measures the incoming particles and magnetic field in the solar wind. The top graph shows the vertical part of the magnetic field (Bz).

Check the current data for Bz. During calm space weather conditions, this graph will be positive—that is, above the white line—indicating a north-pointing magnetic field. A south-pointing Bz may indicate an incoming geomagnetic storm; look for places where the graph dips below the zero line, into the negative region. The more negative this graph reads, the greater the chance of effects here on earth.