Early in my career as a radio enthusiast, back in the 1990s, I occasionally heard a "chirping" sound with a decreasing pitch on the 11-meter CB band. I could hear this phenomenon primarily when receiving single-sideband (SSB) signals during times of good long-distance propagation. Even then, I suspected it was an ionophere phenomenon.
With the advent of web-based SDR receivers, which display a waterfall plot of the frequency spectrum in addition to the audible signal, I was able to rediscover these signals, especially above 20 MHz. I then realized that a distinction must be made between the "chirping" of so-called "floating radio buoys" and the signals that are actually of interest. The radio buoys usually have a stronger, more regular signal, while the radio transmissions from burning meteorites typically have a weaker signal and leave different patterns in the waterfall plot. In the vast majority of cases, the frequency of the "chirping signal" decreases as its intensity diminishes.
What causes this phenomenon?
In my opinion, burning meteorites have an ionized tail with a certain electron density within it. Perhaps through interactions with the Earth's magnetic field, internal instabilities, turbulent currents, or electrostatic discharges, the plasma is stimulated at its resonant frequency, generating these "radio bursts." Since the density of the ionized meteorite tail decreases continuously, both the frequency and the intensity decrease. The fact that this phenomenon can be observed in the frequency range around 28 MHz suggests that an ionized meteorite tail has an electron density (ne) of approximately 10⁷ cm³.
1* radio buoys / 2* radio meteorites (?)
For this image I used the web-SDR of SM1OII in Hablingbo, Gotland Island, Sweden An expert at the Leibniz Institute for Atmospheric Physics in Kühlungsborn, Germany, was kind enough to read the article above. He pointed out to me that radio emissions from plasma have been observed. However, they were rarely detected and these require considerable technical effort as well as a significant antenna gain. Furthermore, reflections of radio signals from the ionized meteorite tail could be mistakenly interpreted as radio emissions.
At this point, I refer to the scientific publication entitled "Association Between Meteor Radio Afterglows and Optical Persistent Trains" by K. S. Obenberger, J. M. Holmes, S. G. Ard, J. Dowell, N. S. Shuman, G. B. Taylor, S. S. Varghese, and A. A. Viggiano.
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JA028053Here you can find web-SDR: http://kiwisdr.com/.public/
