The Kp-index describes the disturbance of the Earth’s magnetic field caused by the solar wind. The faster the solar wind blows, the greater the turbulence. The index ranges from 0, for low activity, to 9, which means that an intense geomagnetic storm is under way.
The following information – from the book Your Guide to the Northern lights and night sky above Iceland (published in early 2019)– describes how different Kp-indices look like as seen from Iceland:
- Kp 0 – Quiet – Aurora oval mostly to the north of Iceland. Faint aurorae visible in photographs, low in the northern sky
- Kp 1 – Quiet – Aurora oval over Iceland, faint and quiet aurorae visible to the unaided eye low in the northern sky
- Kp 2 – Quiet – Auroras readily visible and become brighter and more dynamic
- Kp 3 – Unsettled – Bright auroras visible at zenith. Pale green colour more obvious
- Kp 4 – Active – Bright, constant and dynamic northern lights visible. More colours start to appear
- Kp 5 – Minor storm – Bright, constant and colourful aurora display, red and purple colours appear. Aurora coronae likely
- Kp 6 – Moderate storm – Bright, dynamic and colourful aurora display. Aurora coronae likely. Memorable to those who witness them
- Kp 7 – Strong storm – Bright, dynamic and colourful aurorae. Visible in the southern sky. Aurora coronae very likely
- Kp 8 – Severe storm – Bright, dynamic and colourful aurorae. Aurora seen around 50° latitude
- Kp 9 – Intense storm – Aurorae seen around 40° latitude. Red aurorae and coronae very likely. Most often caused by powerful coronal mass ejections.
It’s important to note that the Kp-index does not definitively predict the strength of the Northern Lights. It nevertheless provides a good idea of what to expect. Always take a Kp-index forecast with a pinch of salt.
The data below shows the K-index for the past week, as measured from Leirvogur Magnetic Observatory.