The first science results from the Solar Eclipse QSO Party (SEQP) last August 21 have been published in the American Geophysical Union journal Geophysical Research Letters. In the paper, “Modeling Amateur Radio Soundings of the Ionospheric Response to the 2017 Great American Eclipse,” Nathaniel Frissell, W2NAF, and team present Reverse Beacon Network (RBN) observations of the SEQP and compare them with ray tracings through an eclipsed version of the physics-based ionospheric model SAMI3. Frissell, a New Jersey Institute of Technology (NJIT) research professor, explains that ray tracing is a method of calculating where a radio wave will go based on electron density — essentially the same as calculating how a light ray through a lens. HamSCI, the Ham Radio Science Citizen Investigation organization, sponsored the event.

“From a ham radio perspective, this paper very clearly shows the effect of the eclipse on not just a few, but a very large number of contacts,” Frissell told ARRL. “You can see from the charts that activity drops off steeply on 20 meters during eclipse totality, while 80 and 160 meters open up. On 40 meters, you can see how the contact distance increases in step with the eclipse.”

Frissell said another key aspect of the paper is that the researchers were able to use ray tracing to compare the observations to a physics-based numerical model of the eclipsed ionosphere. “We did this by ray tracing hundreds of thousands of ray paths on the NJIT supercomputer,” Frissell explained. “The development of this method of comparison also gives us a new tool for comparing datasets like the RBN to actual models.”

On 14 MHz (20 meters), eclipse effects were observed as a drop off in communications for an hour before and an hour after eclipse maximum. On 7 MHz (40 meters), typical path lengths extended from about 500 kilometers (310 miles) to 1,000 kilometers (620 miles) for 45 minutes before and after eclipse maximum. On 1.8 MHz (160 meters) and 3.5 MHz (80 meters), eclipse effects were observed as band openings 20 to 45 minutes around eclipse maximum.

By using ray tracing to compare these observations with the SAMI3 model, it was found that the majority of 14 MHz signals refracted off the ionosphere at heights less than 125 kilometers (77.5 miles) in the E region. On the lower bands, 1.8, 3.5, and 7 MHz, it was found that signals likely refracted off heights greater than 125 kilometers (77.5 miles) in the F region.

These observations suggest an eclipse-induced weakening of the ionosphere, and are consistent with numerous prior HF radio eclipse ionospheric studies.

The SEQP generated more than 618,000 RBN spots, 630,000 Weak Signal Propagation Reporter Network (WSPRNet) spots, 1.2 million PSK Reporter spots, and 29,000 log contacts.

The SEQP research paper, along with the geo-located RBN data with solar eclipse obscuration values used in the paper, are being published under an open-access license to allow for further research. The data files can be found under the “Supporting Information” section of the paper. Additional HamSCI eclipse data is available online.