Understanding the third harmonic near 20 Hz and higher frequencies
The third Schumann resonance is often quoted as 20.8 Hz. Measured averages sit closer to 20 Hz. What the third and higher modes are, how to spot them on a live chart, and what the brainwave comparison does and does not mean.
The third Schumann resonance is the third natural peak of the electromagnetic cavity between the ground and the ionosphere. It is often quoted as 20.8 Hz, but measured averages are lower: the Tomsk station reports a long term mean of 20.23 Hz for 1997 to 2023. Like the other peaks, it moves slightly with the time of day, the season and solar activity.
What the “harmonics” are
The Schumann resonance is not a single tone. Lightning, about 50 flashes every second worldwide, sends low frequency radio waves around the planet. Waves that fit the size of the cavity between the ground and the ionosphere reinforce each other, and this happens at a series of frequencies, called modes (Price 2016).
People often call the higher modes “harmonics”. Strictly, they are not whole-number multiples of the first one: the third mode is not 3 × 7.83 Hz. In Schumann’s idealised formula the mode frequencies depend on n(n+1), where n is the mode number, and the real cavity loses energy, which pulls every peak lower than the ideal value (Price 2016).
Measured values versus the popular numbers
The Tomsk station in Siberia, which has monitored these frequencies since March 1997, publishes a table that makes the point well (sos70.ru):
| Mode | Schumann’s ideal formula (1952) | Balser and Wagner (1960) | Tomsk average (1997 to 2023) |
|---|---|---|---|
| 1st | 10.6 Hz | 7.8 Hz | 7.75 Hz |
| 2nd | 18.3 Hz | 14.1 Hz | 14.17 Hz |
| 3rd | 25.9 Hz | 20.3 Hz | 20.23 Hz |
| 4th | 33.5 Hz | 26.4 Hz | 25.88 Hz |
A review by Palmer and colleagues gives slightly different values for the same 1960 measurements: maxima near 7.8, 14.2, 19.6, 25.9 and 32 Hz (Palmer et al. 2006). Different stations, instruments and analysis methods give slightly different numbers. None of these series puts the third mode at 20.8 Hz. A fair summary is “about 20 Hz”. The fourth mode is about 26 Hz, and the fifth about 32 to 33 Hz.
How the third mode behaves
- It moves a little over the day and the year. Tomsk reports that each resonance frequency has a yearly pattern and a daily pattern (sos70.ru).
- It reacts to the Sun. During solar X-ray bursts in 2001, the first mode rose by about 0.2 Hz and the second by about 0.3 Hz on average, measured in the Kola Peninsula and Kamchatka (Roldugin et al. 2004). Shifts of this size are tenths of a hertz, not jumps to a new frequency.
- Tomsk tracks the first four modes. Every three minutes its processing derives the frequency, amplitude and quality factor (how sharp the peak is) of modes one to four from spectra between 6 and 32 Hz (sos70.ru).
How to find it on a live chart
On the Tomsk chart at sos70.ru, frequency runs from 0 Hz at the top to 40 Hz at the bottom. The first band sits near the 8 Hz mark. Counting down, the third band is the one near 20 Hz.
The station’s own reading guide is worth knowing: white vertical stripes come from a local thunderstorm, black stripes mean missing data, and thin horizontal lines are man-made interference from nearby power lines and machinery. A bright patch around 20 Hz during one of those white stripes is lightning near the station, not a change in the third mode.
The brainwave comparison
You will often read that the third mode “sits in the beta brainwave range”. The numbers do overlap: the international EEG glossary places the beta band at up to 30 Hz and the gamma band above 30 Hz (Kane et al. 2017). So the third and fourth modes fall inside the beta range, and the fifth sits near the lower edge of gamma.
An overlap of numbers is not evidence of an effect. Palmer and colleagues found direct effects of natural low frequency fields “implausible” and thought some form of resonant absorption more likely. They also looked at the hypothesis, put forward by Neil Cherry in 2002, that the brain absorbs the Schumann signal, and said it cannot be accepted until a specific biophysical mechanism is identified (Palmer et al. 2006). We know of no study showing that the natural third mode changes focus, clarity or any other mental state.
Audio tracks and devices sold as “20 Hz” or “Schumann” products are artificial signals. Whatever they do, they do not tell you anything about the natural resonance.
Frequently asked questions
Is the third Schumann harmonic 20.8 Hz? It is often quoted that way. Measured averages are lower: 20.23 Hz at Tomsk over 1997 to 2023, and about 20 Hz in the first clear measurements of 1960.
Why is it not exactly three times 7.83 Hz? Because the modes follow the geometry of a spherical cavity, not a simple string, and because energy losses in the ionosphere lower all of them.
Can the third mode suddenly rise to 30 or 40 Hz? No measurement series we know of shows that. Measured shifts are in the range of tenths of a hertz. A bright column reaching the bottom of the Tomsk chart is a strong burst across all frequencies, usually lightning near the station.
Where can I see all the modes together? The live spectrogram on the home page shows them, and our guide to the current Schumann reading explains how to read it.
Sources
- Space Observing System 70, Tomsk: history and table of measured frequencies, seasonal and daily variations, measurement method and how to read the ELF sonogram (in Russian).
- Price, C. (2016). ELF Electromagnetic Waves from Lightning: The Schumann Resonances. Atmosphere 7(9), 116. doi:10.3390/atmos7090116
- Palmer, S. J., Rycroft, M. J., Cermack, M. (2006). Solar and geomagnetic activity, extremely low frequency magnetic and electric fields and human health at the Earth’s surface. Surveys in Geophysics 27, 557 to 595. doi:10.1007/s10712-006-9010-7
- Roldugin, V. C. et al. (2004). Schumann resonance frequency increase during solar X-ray bursts. Journal of Geophysical Research: Space Physics 109(A1). doi:10.1029/2003JA010019
- Kane, N. et al. (2017). A revised glossary of terms most commonly used by clinical electroencephalographers and updated proposal for the report format of the EEG findings. Clinical Neurophysiology Practice 2, 170 to 185. doi:10.1016/j.cnp.2017.07.002
- Balser, M., Wagner, C. A. (1960). Observations of Earth-Ionosphere Cavity Resonances. Nature 188, 638 to 641. doi:10.1038/188638a0