As everyone knows, the intense solar flares that occurred in early October were widely reported. Even those who are not familiar with solar activity would have heard about them from news reports. The primary way that solar activity affects the shortwave frequency band is through flares and coronal mass ejections (CMEs). The events of early October provide amateur radio enthusiasts with an excellent opportunity to observe these phenomena closely.
First, let's start with some background knowledge to understand what solar activity can affect radio wave propagation.
Solar flares are intense electromagnetic radiation bursts originating from active regions on the Sun. When a solar flare occurs, electromagnetic energy propagates at the speed of light, and when humans observe this phenomenon, the electromagnetic energy simultaneously reaches Earth. Because shortwave radio waves refract through the ionosphere, in areas with sunlight, the electromagnetic energy from solar flares will cause increased ionization in the D layer, which is located at the bottom of the ionosphere, increasing its ability to absorb radio waves, resulting in radio interference. Therefore, if a solar flare occurs, the propagation of shortwave frequencies (especially lower frequencies) will be significantly affected. The level of a solar flare is determined by the peak flux of X-rays.
Sometimes, solar activity can also produce CME (coronal mass ejections). The corona ejects large amounts of plasma. If some of the plasma is moving fast enough to be ejected into interplanetary space and directed towards Earth, these materials will interact with Earth's magnetic field, producing geomagnetic disturbances (storms) and phenomena such as auroras. Geomagnetic storms can disrupt the ionosphere, affecting shortwave signals transmitted through it in various ways. Generally, the parameters used to measure geomagnetic activity are the K-index and the A-index. The K-index (ranging from 0 to 9) measures geomagnetic activity over the past 3 hours, while the A-index (ranging from 0 to 400) is a weighted average of the K-index, which can be considered as geomagnetic activity over the past day. Finally, the intensity of geomagnetic storms is measured using the G-scale (ranging from 1 to 5).
Okay, now that we've covered the necessary background information, let's look at a diagram.
The data in this image comes from my own radio, which is constantly monitoring the 10m band at 28.074MHz using FT8. The antenna is a 3-element Yagi, pointed towards Europe. Software such as JTDX decodes the signals and stores all the decoded data in log files named after the month, so I wrote a small script to analyze these log files and extract the time and distance information for each received signal. The background data shows the K index, along with some key solar activity information at specific times, for reference. This information comes from solarham.com, which is a very good website that summarizes solar activity observations by amateur radio enthusiasts.
From the graph, we can see that, due to the relatively high frequencies in the 10-meter band, the effect of solar flares on D-layer absorption at the time was not apparent. However, when a large geomagnetic storm occurred, the entire frequency band disappeared, and only a few radio stations could be received. Because my conditions were limited, if I could compare it with a lower frequency band (such as 20 meters), the effects of both solar activity might be more noticeable. Furthermore, we can observe that before the geomagnetic storm began, DX propagation showed an improving trend, which is similar to what some older HAMs and my own observations have shown. However, I cannot provide a scientific explanation for this.
Here's a brief advertisement: I proposed the idea of using software analysis to decode FT8 logs and determine propagation trends for my own station in 2022, and I released the first version of the script, JLP, that year. However, as JTDX and WSJT-X software have been updated, older versions of JLP can no longer handle new log files. I am currently rewriting the software and hope to add more features. I expect to be able to share it with everyone by the end of this year. I look forward to a future where every region has a large, flagship radio station running a multi-band FT8 skimmer that calculates an opening chart for local enthusiasts, making it easier for them to find optimal communication windows in a more scientific way.
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