St. Elmo’s Fire Weather Phenomenon   Recently updated !


St. Elmo’s Fire
St. Elmo’s fire is luminous plasma, usually around a rod-shaped object or aircraft, caused by ionization of air.

St. Elmo’s fire is a captivating weather phenomenon that intrigues sailors, pilots, and scientists. Known for its ghostly blue or violet glow, this electrical event occurs under specific atmospheric conditions, including thunderstorms and volcanic eruptions. Despite its ominous appearance, St. Elmo’s fire is not harmful. In fact, sailors considered it to be a good omen.

  • St. Elmo’s fire is a continuous blue or violet electrical glow around pointed objects during thunderstorms or other electrical conditions.
  • It gets its name for St. Elmo, the patron saint of sailors, as it commonly occurs on ship masts and is considered a good omen.
  • The bluish violet plasma glow results from the ionization of nitrogen and oxygen in air.
  • Although it resembles lightning, it is not the same thing. A plasma ball toy is comparable to St. Elmo’s fire, although it is a different color due to the gases the ball contains.

What Is St. Elmo’s Fire?

St. Elmo’s fire is a continuous, luminous plasma discharge in the atmosphere. It typically appears as a bluish or violet glow around pointed objects such as ship masts, aircraft wingtips, church steeples, and even the horns of cattle. Sometimes lightning-like discharges occur, but the coronal glow is the “fire.” Often, a hissing. buzzing, or crackling sound accompanies the light. The phenomenon occurs when the air becomes electrically charged, usually during thunderstorms or other conditions that create a high electrical field.

Other Names and Origin of the Term

The phenomenon takes its name after St. Erasmus of Formia, also known as St. Elmo, the patron saint of sailors. Sailors considered the appearance of the glow on their ship’s mast as a sign of protection from their patron saint. Another term for the glow is “corposants,” which comes from the Portuguese and Spanish words for “holy body.” Another common name for St. Elmo’s fire is “witch fire.”

St. Elmo’s Fire vs. Lightning and Ball Lightning

While St. Elmo’s fire, lightning, and ball lightning are all forms of plasma, they differ in their appearance, cause, and properties. Visually, the biggest difference is that lightning and ball lightning are short-lived, while St. Elmo’s fire persists for minutes or even hours.

  • St. Elmo’s Fire: A continuous, faint glow around pointed objects during electrically charged conditions.
  • Lightning: A powerful, transient electrical discharge between clouds or between a cloud and the ground, accompanied by a bright flash and thunder.
  • Ball Lightning: A rare and mysterious phenomenon involving a glowing, spherical object that moves independently and can last several seconds.

Historical Observations

Historical records of St. Elmo’s fire date back to ancient times. Greek sailors noted the phenomenon and associated it with the gods. During the Age of Exploration, European sailors frequently observed St. Elmo’s fire and regarded it as a good omen. Probably this was because the glow was not dangerous and it often indicated the worst of the storm had passed. Pilots during World War II also reported seeing the glow on their aircraft. There are numerous modern photographs and videos of St. Elmo’s fire.

How St. Elmo’s Fire Works

St. Elmo’s fire occurs due to ionization of the air by a strong electrical field.

During thunderstorms, the electric field around pointed objects becomes extremely strong. When this field exceeds a critical value, it ionizes the air molecules around the object. Ionization occurs when the electric field strips electrons from air molecules, which primarily consist of nitrogen (N2) and oxygen (O2). This process creates positively charged ions and free electrons. The free electrons and ions recombine, releasing energy in the form of photons (light). The specific wavelengths of light depend on the energy levels of the ions involved. When ionized nitrogen molecules recombine, they emit light primarily in the blue and violet regions of the spectrum. Oxygen ions also contribute to the blue and violet glow, though to a lesser extent than nitrogen.

Is St. Elmo’s Fire Dangerous? Can You Touch It?

St. Elmo’s fire itself is not dangerous, as it is a low-current electrical discharge. It does not pose a significant risk to aircraft because they have shielding and grounding against electrical phenomena. Anecdotally, touching it causes a tingling sensation, similar to static electricity.

When and Where to See St. Elmo’s Fire

St. Elmo’s fire is a rare event. To see it, your best chances involve thunderstorms and volcanic eruptions, which involve high atmospheric electricity. Viewing is easier at night or with dim light. Places to see it include:

  • At Sea: Ship masts and rigging during thunderstorms.
  • In the Air: Aircraft wingtips, propellers, or windshields during flights through electrically charged clouds.
  • On Land: Church steeples, weather vanes, and other tall, pointed structures during stormy weather. Volcanic eruptions create strong electrical fields through the friction of ash particles in the volcanic plume, leading to St. Elmo’s fire around the volcano’s summit or nearby pointed objects.

References

  • Eyers, Jonathan (2011). Don’t Shoot the Albatross!: Nautical Myths and Superstitions. London: A&C Black. ISBN 978-1-4081-3131-2.
  • Guerra-Garcia, C.; Nguyen, N. C.; et al. (2020). “Corona Discharge in Wind for Electrically Isolated Electrodes”. Journal of Geophysical Research: Atmospheres. 125 (16). doi:10.1029/2020JD032908
  • Wescott, E.; et al. (1996). “The optical spectrum of aircraft St. Elmo’s fire”. Geophys. Res. Lett. 23(25): 3687–90. doi:10.1029/96GL03621