What is a Geomagnetic Storm?
A "Geomagnetic Storm" is a period of rapid magnetic field variation that can last from hours to days.
Illustration of a Geomagnetic storm as seen from earth close to polar regions (public domain images):
What are the impacts of a geomagnetic storm?
A major geomagnetic storm can disrupt HF propagation by changing the distribution of free electrons in the ionosphere. It may also trigger auroras
.
A storm has three phases: initial, main, and recovery.
What causes a geomagnetic storm? — Solar radiation bursts and solar energetic particles:
- Solar X-Ray radiation bursts known as solar flares:
- Solar plasma particles colliding with Earth's Magnetosphere. Significant events are named "Coronal Mass Ejections" (CME) :
A Solar Flare courtesy of NOAA, May 2023
A CME is a shock-wave of Solar Energetic Particles emitted by the sun.
When a CME enters the magnetosphere, it causes a Geomagnetic Storm
How is geomagnetic storm defined?
A geomagnetic storms are defined by changes in the "Disturbance-storm time" (Dst) index. The Dst index estimates the globally averaged change of the horizontal component of the Earth's magnetic field at the magnetic equator based on measurements from a few magnetometer stations. Dst is computed once per hour and reported in near-real-time.
How is a geomagnetic storm classified?
At a quiet time (no storm) the magnetic field ranges from +20 to −20 nano-Tesla (nT). The magnitudes of storms are classified as moderate (from 50 nT to 100 nT), intense (from 100 nT to 250 nT), or super-storm (above 250 nT).
How is a geomagnetic storm quantified?
The Kp index quantifies the geomagnetic disturbances, "correlating with G-scale".
What was the strongest geomagnetic storm in history?
The "Carrington Event" was the most profound geomagnetic storm ever recorded, peaking on September 1–2, 1859, during solar cycle 10. There were several global accounts of its powerful auroral displays, as well as the sparks and fires it generated in telegraph stations. Wireless radio transmissions were unknown at that time.
When was the last geomagnetic storm?
The strongest geomagnetic storm in over two decades dazzled scientists and sky-watchers alike in May 2024. The G5 storm culminated in a remarkable display of the aurora overnight on May 10–11, visible from many areas worldwide, including latitudes where sightings of auroras are uncommon.
Alerting about the G5 Storm, May 10 2024
Geomagnetic Storms from May 11 to May 13, 2024
Observed K index
Observed A index
Kp Index
- References:
- May 2024 Solar Storms Wikipedia
- Geomagnetic Storms May 2024 Duckduckgo