The earth hums with a quiet, rhythmic beat somewhere between the heavens and the ground beneath our feet. It is an electromagnetic song, played in the vast space between Earth’s surface and the ionosphere. This natural phenomenon, called Schumann resonances, is like the planet’s background music — subtle, constant and often overlooked.

Schumann resonances are a set of extremely low-frequency electromagnetic waves that circle Earth, trapped in the cavity formed by the planet and ionosphere — its electrically charged upper atmosphere. They occur because the space between the surface of Earth and the conductive ionosphere acts as a closed, although variable-size, waveguide.

First predicted by German physicist Winfried Otto Schumann in 1952, these waves are generated by lightning strikes that occur around the globe every second.

At any given time there are about 2,000 thunderstorms around the world, producing approximately 50 lightning events per second. Each strike sends a pulse of electromagnetic energy into the cavity, where it resonates between Earth and the ionosphere, reinforcing itself like sound waves resonating inside a musical instrument.

The fundamental frequency of Schumann resonances is about 7.83 hertz, with additional harmonics at roughly 14, 20, 26, 33 and 39 hertz. Although we cannot hear them, they are always present, forming a steady electromagnetic heartbeat of the earth.

Schumann resonances overlap with the frequency range of brain waves. The 7.83-hertz fundamental frequency is close to the low end of the alpha wave range, which is associated with relaxed and meditative states in humans.

This has led to speculation about whether these natural electromagnetic fields might influence human health or consciousness. However, while some studies have explored possible links between Schumann resonances and biological rhythms, no definitive scientific evidence supports such claims.

Schumann resonances provide a unique window into Earth’s electrical activity. Because they are influenced by lightning, changes in their intensity can indicate shifts in global weather patterns and even climate change. Researchers have found correlations between variations in these resonances and natural events such as solar storms, which can alter the ionosphere and affect how these waves propagate.

Because Schumann resonances are a global phenomenon, scientists can use them to study changes in Earth’s electrical properties. This has practical applications for monitoring space weather, detecting large-scale disturbances in the ionosphere and even predicting extreme weather events.

Schumann resonances have been used to track global lightning activity. Because lightning activity and Earth’s climate are interrelated, the resonances may be useful to monitor global temperature variations and variations of water vapor in the upper troposphere. (The troposphere is the lowest layer of Earth’s atmosphere.)

In addition to their scientific importance, Schumann resonances serve as a reminder of how interconnected Earth’s systems are. They are shaped by electrical activity in the atmosphere, influenced by solar radiation and affected by natural and human-induced changes to the environment.

While they remain largely unnoticed in daily human life, Schumann resonances provide an ever- present pulse that scientists can tune into, a silent yet powerful rhythm that speaks to the dynamic nature of our planet.

The next time you see lightning crack the sky, remember that its energy is not just a fleeting flash. Like a plucked string on a guitar, it is part of a global electromagnetic symphony that has been playing for millions of years.

Richard Brill is a retired professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.