REFERENCE — FREQUENCIES
Schumann resonance frequencies
The Earth–ionosphere cavity supports five well-established standing-wave modes. Their nominal frequencies, typical observed ranges and physical meaning — the reference table used across this observatory.
| Mode | Nominal | Observed range | Wavelength | Q factor |
|---|---|---|---|---|
| SR1 — Fundamental | 7.83 Hz | 7.2 – 8.1 Hz | ≈ 38,300 km | ~4.6 |
| SR2 — First overtone | 14.3 Hz | 13.6 – 15.0 Hz | ≈ 21,000 km | ~5.1 |
| SR3 — Second overtone | 20.8 Hz | 19.8 – 21.8 Hz | ≈ 14,400 km | ~5.7 |
| SR4 — Third overtone | 27.3 Hz | 26.0 – 28.5 Hz | ≈ 11,000 km | ~6.0 |
| SR5 — Fourth overtone | 33.8 Hz | 32.3 – 35.2 Hz | ≈ 8,880 km | ~6.4 |
Where the numbers come from
Nominal values follow the classical cavity model (wave speed ≈ c in the gap, effective ceiling height ≈ 85–90 km) refined by decades of measurement — from Balser & Wagner's 1960 MIT spectra to modern induction-coil stations in Greenland, Antarctica and Sodankylä. Observed ranges reflect real diurnal and seasonal variation: every mode breathes with the ionosphere.
What shifts each mode
Day/night cycle — the nighttime ionosphere rises, lowering each frequency by 0.05–0.2 Hz. Solar X-rays and geomagnetic storms — sudden ionization changes can sharpen, split or amplify modes; watch SR2–SR5 during active Kp. Lightning geography — the three great "chimneys" (Central Africa, Maritime Continent, South America) modulate the amplitude of every mode on a daily schedule, peaking near 14:00 UTC when Africa storms dominate.
How to read them live
On the live observatory: the sonogram shows all five modes as horizontal ridges between 0 and 40 Hz; the harmonic chart tracks each mode's drift over 24 hours; the deviation band isolates SR1's movement around 7.83 Hz. All values update continuously from the observatory engine, with space weather verified against NOAA SWPC.
Related pages
What is the Schumann resonance? — the full physics primer. · Live monitor — today's values, sonogram and charts. · Free JSON API (CC0) — all frequencies, no key required.