Understanding Coronal Holes and Their Impact on HF Propagation
We’re about HF radio here, so let’s get to it
At SolarCdx.com, we are dedicated to providing insights into solar activity and its real-world effects on HF Radio. Today, we’re diving into the fascinating world of Coronal Holes (CHs) and explaining why understanding them is crucial, especially for anyone involved in High-Frequency (HF) radio propagation.
What Exactly is a Coronal Hole?
A Coronal Hole is an area in the Sun’s upper atmosphere, or corona, that appears darker in extreme ultraviolet (EUV) and soft X-ray images. This happens because the plasma is less dense and cooler. The key characteristic of a CH is its open, unipolar magnetic field lines that stream high-speed solar wind into space. This solar wind, traveling at high speeds, is what primarily impacts Earth’s magnetic field and, consequently, our radio communications.
The Olden Days…For the last 54 years…..
HelioPhysicists have been creating maps of the sun for over 50 years. They use various technologies, including telescopes, visual images, and satellite data, to generate these detailed maps. Solar Synoptic Maps, in particular, have been hand-drawn for decades and continue to be produced this way today.
How our system works
Our Coronal Hole Detector is an automated system that identifies these regions. Using advanced image processing, we can detect CH signatures and image them. Here’s a look at how it operates:
Multi-Wavelength Data: The detector uses three EUV wavelengths from NASA’s Solar Dynamics Observatory (AIA 171Å, 193Å, 211Å) plus magnetic field data from the HMI instrument. Humans can’t do Multi-channel coronal hole detection by looking at images. - Image Fusion: These data layers are processed together to highlight regions where coronal holes are present.
- Python Implementation: Originally designed as the CHIMERA algorithm, this tool has been re-engineered into a modern Python workflow for speed, accuracy, and reliability on SolarCdx.com. The original program is wonderful if you are a HelioPhysicist, but we’re HAMS.
- Automated Updates: SolarCdx.com downloads the latest FITS files, processes them, and generates new annotated solar images every cycle. Usually 20-30 minutes.
A little CH Matters too!
Sometimes there’s a very minimal effect on the Earth from a CH, usually an increased Solar Wind Speed. But even that has an effect on HF propagation. As Coronal Holes rotate away from Earth, their effects diminish but may still cause HF disruptions.
The SolarCdx.com Multi-Parameter Correlation Engine for HF Propagation Intelligence, The Disturbance Factor, also detects the signatures of CH events.
As you can see here, our system has detected a “Marginal CH Signature”, indicating that as the CH is likely rotating away, HF radio will be getting better soon.
Why It Matters to HF Radio Operators
For HF operators, CHs aren’t just an academic curiosity; they can significantly disrupt your communication plans. The high-speed solar wind from CHs can push Earth’s magnetic field, leading to geomagnetic storms. These storms can cause increased radio signal absorption and poorer propagation. Different HF bands are affected differently:
- 160m & 80m: These lower bands are often the first to experience increased absorption and fading.
- 40m & 20m: These bands can go from open worldwide to completely closed, even during daylight hours.
- 15m, 12m & 10m: These higher bands are sensitive to geomagnetic storms, which can completely close them.
For a deeper dive into our detection system, you can visit
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Good Dx, 73
