BASTILLE DAY SOLAR EVENT
At mid-day on July 14, 2000, a major mass ejection from the central part of the Sun's disk was observed by various solar imaging instruments, some of which were located on spacecraft. Since this is the day celebrated by the French as Bastille Day (July 14, 1789 was the beginning of the French Revolution and July 14 is equivalent to the American 4th of July.), the solar event was called the Bastille Day Event. Thirty two hours later the material ejected was seen in the vicinity of Earth. This mass and the solar magnetic field embedded in it (called a magnetic cloud) had many extreme properties seldom seen in such material. In the figure below we show the quantities B (the solar wind magnetic field intensity), BZ (the north-south component of that field), the solar wind speed (V) and a geomagnetic activity index (Dst), which is a good indicator of when magnetic storms occur (i.e., when Dst £
-50 nT, a storm is considered to have occurred). On July 15, Dst went below -300 nT indicating a gigantic magnetic storm occurred. A strong shock wave occurred 4.5 hours before the start of the magnetic cloud (see MC2) and pushed in the magnetosphere of the Earth. During the cloud, which was very fast, the outer boundary of the magnetosphere was pushed so low on some occasions that geosynchronous satellites briefly appeared outside the Earth's magnetosphere - on the frontside.
This page last updated July 20, 2001