St Elmo's Fire: what is the rare weather phenomenon - as it is captured in Florida amid Hurricane Idalia

Just as the people of Florida brace themselves for what forecasters say is the extremely dangerous Hurricane Idalia, they had the opportunity to bask in the glory of a rare and truly remarkable weather phenomenon - the St Elmo's fire.

Pilots captured the electrical display at MacDil Air Force Base near Tampa in the US state on Tuesday (August 29). They recorded the unbelievable sight from the cockpit and the video has since gone viral on social media.

In a post on X - formerly known as Twitter - the Air Force Base wrote: "During the evacuation, the 50th ARS recorded St. Elmo’s fire, a weather phenomenon in which luminous plasma is created in an atmospheric electric field."

But what is the St Elmo's fire, what causes it and what does it typically look like? Here is everything you need to know about the magnificent rare weather phenomenon.

What is the St Elmo's fire and what does it look like?

St Elmo's fire - typically referred to as Witchfire or Witch's Fire - is a rare weather phenomenon which sees luminous plasma created by corona discharge from a rod-like object in an atmospheric electric field. If you are lucky enough to observe the electrical display, it is often seen on the edges of airplanes.

The phenomenon has a blue or violet glow and accompanied by a hissing or buzzing noise. Due to the intensity needed, it is far more likely to be visible during natural events like thunderstorms and volcanic eruptions and can be a sign of an imminent lightning strike.

Why is it called St Elmo's fire?

It has been given its name after St Erasmus of Formia (also known as St Elmo) who is the patron saint of sailors. The phenomenon was regarded as a good omen by sailors, who would be in awe of the display.

What causes St Elmo's fire?

The rare weather spectacle is considered a reproducible and demonstrable form of plasma that are generated in conditions when high-voltage differentials are present between clouds and the ground like thunderstorms. Experts say that an electric field of around 100 kV/m is needed to begin a discharge in moist air.

As areas of high curvature require less voltage, St Elmo's fire typically are more intense on pointed objects. The Massachusetts Institute of Technology (MIT) found in an August 2020 paper that it behaves differently in airborne objects compared to grounded structures.