Definition
The Schumann resonance is the natural electromagnetic resonance of the cavity between Earth's surface and the lower ionosphere. It consists of a set of frequencies in the Extremely Low Frequency (ELF) range, with a fundamental at about 7.83 Hz. These standing waves are continuously excited by global lightning activity and can be measured from anywhere on Earth.
Simple Explanation
Think of the space between the ground and the ionosphere as a spherical shell. Lightning around the world sends out electromagnetic pulses. Only those frequencies that "fit" once, twice, or more times around the planet are reinforced; the rest cancel out. The lowest of these is about 7.83 Hz—the Schumann fundamental. So the Schumann resonance is essentially Earth's electromagnetic "heartbeat" driven by thunderstorms.
Link to Thunderstorms
Roughly 50 lightning flashes per second occur globally. Each flash radiates a broad range of frequencies; the component at the cavity's resonant frequencies is amplified as it travels around the Earth. So the Schumann resonance reflects global thunderstorm distribution. When storm activity is high, amplitudes rise; when it is low or shifted, they fall. There is no single "source"—it is the sum of all lightning.
The 7.83 Hz Frequency
The value 7.83 Hz comes from the circumference of the Earth and the effective propagation speed of ELF waves in the cavity. One wavelength at this frequency fits once around the planet. Small variations (e.g. 7.8–7.9 Hz) occur because ionosphere height and conductivity change with time of day, season, and space weather. So 7.83 Hz is the typical value, not a constant.
Why It Matters
The Schumann resonance is used in geophysics to study the Earth–ionosphere cavity and global lightning. It also appears in discussions of space weather, because ionospheric disturbances (e.g. from solar storms) can affect both the frequency and amplitude of the resonance. Cosmic Radar shows Schumann data in the daily report together with the Kp index and space weather events, so you can see how they relate.
Sources and further reading
- NOAA Space Weather Prediction Center – Forecasts, Kp index, space weather alerts
- Cumiana VLF Station – Live Schumann resonance data
- ESA Space Weather – European monitoring and education