| Bastille Day solar storm | |
| G-Impacts: | Minor satellite and terrestrial power transformer damage |
| Solar-Cycle: | 23 |
| Dst: | −301 nT |
| K-Index: | 9 |
| A-Index: | 164 |
| G-Scale: | 5 |
| Ar-Sxr-Flares: | X5.7 |
| Noaa: | 9077 |
The Bastille Day solar storm was a powerful solar storm on 14–16 July 2000 during the solar maximum of solar cycle 23. The storm began on the national day of France, Bastille Day. It involved a solar flare, a solar particle event, and a coronal mass ejection which caused a severe geomagnetic storm.[1]
On 14 July 2000 from about 10:03 to 10:43 UTC, GOES satellites detected a very strong, X5.7-class, solar flare which peaked in soft X-ray intensity at around 10:24 UTC. This flare originated from the solar active region AR9077 which was located near the center of the Sun's disk (N22 W02) at the time of the flare.[2]
Starting at around 10:41 UTC, GOES satellites began detecting a strong, S3, solar particle event associated with the ongoing X5.7-class flare.[3] This resulted in high energy protons penetrating and ionizing parts of the Earth's ionosphere and creating noise in various satellite imaging systems such as in the EIT and LASCO instruments.[4] Some of these particles had sufficient energy to generate effects measured on Earth's surface, an event referred to as a ground level enhancement. Although the flare was not extremely large, the associated solar particle event was the fourth largest since 1967.[5]
The detection of the solar flare was also followed by the detection of a halo, or Earth-directed, coronal mass ejection (CME) in coronagraph data starting at 10:54 UTC. This CME reached Earth on 15 July causing a geomagnetic storm on 15–16 July which would reach a peak Kp index of 9+ in the late hours of 15 July corresponding to an extreme-level, or G5, geomagnetic storm and register a peak Dst of −301 nT. The storm caused minor damage to power transformers and satellites.[6] It was also one of only three solar storms having registered a maximum Kp of 9+ since the March 1989 geomagnetic storm, the others being the 2003 Halloween solar storms and the May 2024 solar storms.[7]
Due to being the first major solar storm since the launch of various solar-monitoring satellites, the Bastille Day event proved important towards helping scientists piece together a general theory of how eruptions on the sun occur as well as protecting the Earth from a larger event, such as a Carrington-class event, some day in the future.[8]
Despite their great distance from the Sun, the Bastille Day event was observed by Voyager 1 and Voyager 2.[9]