How to Look for a South-pointing Magnetic
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.