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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][2]
 | |
| Associated solar active region | |
|---|---|
| NOAA region no. | 9077 |
| Largest SXR flares | X5.7 |
| G5 "Extreme" geomagnetic storm | |
| G-scale (NOAA/SWPC) | |
| Initial onset | 14 July 2000 |
| Dissipated | 16 July 2000 |
| Peak Kp-index | 9 |
| Peak Ap-index | 164 |
| Peak Dst | −301 nT |
| Impacts | Minor satellite and terrestrial power transformer damage |
Part of solar cycle 23 | |
Solar flare and particle event
On 14 July 2000 from about 10:03 to 10:43 UTC, GOES satellites detected a very strong, X5.7-class solar flare[note 1] 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.[3][4]
Starting at around 10:41 UTC, GOES satellites began detecting a strong, S3, solar particle event[note 2] associated with the ongoing X5.7-class flare.[1] 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.[7] 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.[4]
Geomagnetic storm
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.[7] 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[note 3] and register a peak Dst of −301 nT. The storm caused minor damage to power transformers and satellites.[8] 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.[9]
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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.[10]
Despite their great distance from the Sun, the Bastille Day event was observed by Voyager 1 and Voyager 2.[11]
- The label X5.7-class implies that the solar flare had a peak soft X-ray flux of 5.7×10−3 W/m2 in the 0.1 to 0.8 nm (1 to 8 Å) passband. (See Solar flare § Soft X-ray classification.)
- The label G5 is assigned to geomagnetic storms which reach a peak Kp index of 9 or more.[5] (See K-index § G-scale.)
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