The five Schumann modes — 7.83 to 33.8 Hz

The Earth–ionosphere cavity does not play a single note. Any wave whose wavelength fits a whole number of laps survives as a standing wave, and the result is a family of five resonance modes: a steady fundamental near 7.83 Hz, and overtones around 14.3, 20.8, 27.3 and 33.8 hertz that grow progressively weaker and more restless. This guide walks through each mode's character and shows how to recognize them on the Tomsk spectrogram. For the underlying physics, start with our what is the Schumann resonance page.

Mode I — 7.83 Hz: the fundamental, the "heartbeat"

The fundamental is the cavity's longest standing wave and the star of the spectrum: the brightest line, the steadiest. It is measured everywhere on the planet at nearly the same frequency at the same moment, and that global uniformity has fueled the "Earth's heartbeat" metaphor since the 1970s. On the spectrogram, Mode I is a nearly unbroken horizontal band in the lower part of the chart. Its frequency wobbles by about ±0.5 hertz with season and hour; when a page asks which mode is dominant, the answer is almost always I.

Mode II — 14.3 Hz: the restless one

The second mode sits just below twice the fundamental and behaves completely differently: it is restless. Its amplitude can swing several-fold within hours, its band fragments, and it disappears for stretches at a time. It is far more sensitive than the fundamental to the day–night balance of the ionosphere, which makes it a useful probe for ionospheric research. On the spectrogram, Mode II looks like a breathing band — strong hours, empty hours.

Mode III — 20.8 Hz: the noon peak

The third mode is famous for following the African lightning sector: it strengthens noticeably around the sector's local afternoon hours. It is a weak mode, but its regular hour rhythm makes it a recognizable melodic line on the chart. Watch the upper part of the spectrogram — if a line brightens during Africa's afternoon and fades afterward, you are most likely looking at Mode III.

Mode IV — 27.3 Hz: the faint one

The fourth mode always struggles: low amplitude, a pale and patchy band. It becomes visible mainly when the ionosphere is quiet and well conducting — typically at night and during geomagnetically calm days. Beginners find it the hardest mode to spot; experienced readers treat it as an honest report of ionospheric state.

Mode V — 33.8 Hz: the storm mode

The fifth mode is the storm sentinel at the edge of the spectrum: under ordinary conditions it barely appears, but during intense lightning bursts — especially when tropical storm clusters strengthen simultaneously — it brightens conspicuously. Some readers call it the "storm mode." The hours when Mode V shows are usually the hours when Mode I below is bright too: the energy comes from the same storms.

Why amplitude breathes through the day

Lightning is not distributed evenly across the globe: three great centers concentrate over Africa, Asia and the Americas. Each peaks near its local afternoon, and the three peaks rotate through the UTC day. That rotation drives amplitude swings of up to ~15% in the modes — the panel's breathing is not a glitch but real physics. The live panel on the home page updates the five modes' relative amplitudes every 4 minutes.

The modes at a glance