Through a Crystal Ball
Two significant flares occurred during August 20–21 as a historically active sunspot group returned to the visible face of the sun. The geomagnetic field was disturbed through August 20. The source of the disturbance was a high-speed solar wind stream that originated from a coronal hole on the sun's surface. Spacecraft sensors detected solar wind speeds approaching two million miles per hour. There's a chance for more significant solar flares from the sunspot group during August 25–31 as it continues to trek across the visible face of the sun.
—NOAA/SEC, “Outlook 99-20,” August 24, 1999
When CMEs do make it to the Earth, the compressed magnetic fields and plasma in their leading edges smash into the geomagnetic field like a battering ram. Across a million-mile-wide wall of plasma, the CME pummels the geomagnetic field. Such niceties as whether the polarities are opposed or not make little difference to the outcome. The CME pressure can push the geomagnetic field so that it lays bare the orbits of geosynchronous communication satellites on the dayside of the Earth, exposing them to wave after wave of energetic particles. When the fields are opposed, particles from the CME wall invade the geospace environment, amplify ring currents, and generally cause considerable electromagnetic bedlam, often tracked by increases in the recorded satellite anomalies and power grid GICs. Clearly, we need more advanced warning for solar flares, geomagnetic storms, and CMEs. A successful forecast of how severe a particular solar cycle will