Space weather and its effect on radio communication:
3/6/25:
The 10 metre band has been worse than ever over the last few days. We are just about at the sunspot maximum but you wouldn’t think so. So, what’s this all about? I’ve never looked into so-called space weather but, now I’m active daily with WSPR on 10 metres, I’ve taken an interest. I’ve started by looking at geomagnetic storms and understanding solar wind and the K-Index.
Geomagnetic Storms:
One of the most significant forms of space weather is the geomagnetic storm, a powerful disturbance in Earth’s magnetic field triggered by solar activity. Though invisible to the naked eye, geomagnetic storms can have far-reaching impacts, disrupting satellite communications, interfering with power grids, and affecting aviation systems.
Geomagnetic storms are triggered by bursts of solar wind, streams of charged particles, primarily electrons and protons, that flow outward from the Sun. When these particles collide with Earth’s magnetosphere, the protective magnetic field surrounding our planet, they can cause significant disturbances. Intense solar wind bursts, often originating from coronal mass ejections (CMEs), can severely disrupt the magnetosphere, sparking a geomagnetic storm. These storms can travel from the Sun to Earth in as little as 18 hours, though the journey can take up to 96 hours. Once they arrive, their effects may linger for several days, impacting technology and infrastructure on a global scale.
The K Index:
The K-index is a scale used to quantify short term geomagnetic activity which is measured over three hour intervals. It ranges from 0 to 9 with higher values indicating stronger disturbances in the Earth’s magnetic field. This index is derived from data collected by ground based magnetometers located at observatories around the world. These measurements help assess the influence of space weather phenomena such as solar wind, coronal mass ejections and other solar events, on Earth’s geomagnetic environment.
The lower the K Index number, the better:
A low K-index of 0 to 3 signifies quiet geomagnetic conditions, ideal for HF radio propagation. This is particularly good on the higher bands, 20 metres up to 10 metres. Under these stable conditions, signal paths remain consistent, absorption is minimal and long-distance DX contacts are more reliable. When the K-index rises to 4 or 5 geomagnetic activity becomes unsettled. This leads to increased signal absorption and fading, especially on lower bands such as 160m and 80m. At high K-index values, 6 to 9, geomagnetic storms can severely affect HF communications. Absorption on low bands often becomes extreme, rendering 160m and 80m virtually unusable. Polar blackouts disrupt transpolar DX routes while bands above 20m become increasingly unreliable and are plagued by deep fades and fluctuating signals.
- K = 0 Inactive
- K = 1 Very quiet
- K = 2 Quiet
- K = 3 Unsettled
- K = 4 Active
- K = 5 Minor storm
- K = 6 Major storm
- K = 7 Severe storm
- K = 8 Very severe storm
- K = 9 Extremely severe storm
For your interest. The daily K-index:
At 0900 GMT.
| Date | K-Index | Date | K-Index |
| 3/6/25 | 7 | 13/6/25 | 5 |
| 4/6/25 | 3 | 14/6/25 | 3 |
| 5/6/25 | 2 | 15/6/25 | 2 |
| 6/6/25 | 2 | 16/6/25 | 2 |
| 7/6/25 | 4 | 17/6/25 | |
| 8/6/25 | 2 | 18/6/25 | |
| 9/6/25 | 4 | 19/6/25 | |
| 10/6/25 | 1 | 20/6/25 | |
| 11/6/25 | 3 | 21/6/25 | |
| 12/6/25 | 4 | 22/6/25 |
Solar Wind:
Solar wind speed is between 0-1000 KM/s. The lower the better for radio communication.
Solar wind is a continuous flow of charged particles emitted by the Sun. It interacts with Earth’s magnetosphere and ionosphere, affecting the propagation of electromagnetic waves. This leads to signal fading, absorption, and even blackouts, especially at higher frequencies. Additionally, solar wind influences the propagation of disturbances like coronal mass ejections (CMEs) and solar energetic particles (SEPs), affecting space weather and potentially disrupting satellite communications and power grids.
Ionospheric Effects:
- Solar wind, particularly during solar flares and CMEs, can heavily ionize the Earth’s ionosphere.
- This increased ionization can absorb or scatter HF radio waves, making them less effective for long-distance communication.
- HF radio blackouts can occur, especially on the dayside of Earth, when the Sun is directly overhead.
- The effects are most pronounced at higher frequencies but, below 10MHz, careful frequency selection can minimize disruptions.
- Solar wind also affects the propagation of other signals, like those used in GPS, by altering the refractive index of the ionosphere.
Here’s a website showing solar conditions which is very useful.