These are the lights that can be seen on sharp peaks — ship masts, towers, high rocks. In the Middle Ages they were often seen on the spire of St. Elmo’s cathedral in Germany — providing the name. In this new lesson of the Windy.app Meteorological Textbook (WMT) and newsletter for better weather forecasting you will learn more about what St. Elmo's fire is and how it works.
The lights are electric charges between the spire and dust particles in the air. The spires have to be positively charged and the air around them — negatively, or vice versa.
Let’s recall that:
Before thunderstorm strong air currents cause the collision of dust particles with spires. Upon collision, electrons are passed from the particles to the spires and vice versa.
As a result, a spire can get extra electrons — then it’s negatively charged. If electrons ‘jump’ from the spire to the dust particles, the spire is positively charged.
One more condition is necessary for the electric charges — the air has to carry current. It can happen in two cases:
How does the electric charge pass? The electron that broke away from the spire collides with another object’s atom. The atom’s energy changes — it drops. The glow comes from the energy difference. The more collisions, the brighter it is.
St. Elmo’s fire effect. Illustration: Valerya Milovanova / Windy.app
Text: Windy.app team
Illustrations: Valerya Milovanova, an illustrator with a degree from the British Higher School of Art an Design (BHSAD) of Universal University
Cover photo: Unsplash