What causes the naval phenomenon called St. Elmo's Fire?

St. Elmo's fire is an electroluminescent coronal discharge caused by the ionization of the air during thunderstorms inside of a strong electric field.

Although referred to as "fire", St. Elmo's fire is in fact a low density, relatively low temperature plasma caused by massive atmospheric electrical potential differences which exceed the dielectric breakdown value of air at around 3 megavolts per meter.


https://en.wikipedia.org/wiki/St._Elmo%27s_Fire

St. Elmo's Fire is "caused by the ionization of the air during thunderstorms inside of a strong electric field."
https://en.wikipedia.org/wiki/St._Elmo%27s_Fire

Here is the tail end result of "Real" St Elmos. The phenomena seen is not it but very interesting all the same.

"Physically, St. Elmo's fire is a bright pink-purple glow, appearing like fire in some circumstances, often in double or triple jets, from tall, sharply pointed structures such as masts, spires and chimneys, and on aircraft wings. It is named such because the phenomenon commonly occurs at the mastheads of ships during thunderstorms at sea, and St. Elmo is the patron saint of sailors."

https://en.wikipedia.org/wiki/St._Elmo's_Fire

In Melville's "Moby Dick" and Huston's movie version, St. Elmo's Fire happens during a vicious storm. In the book, Ahab's harpoon catches it and the crew gets scared; Ahab simply blows it out. In the Huston movie, Peck's Ahab threatens Starbuck with a lance when the latter tries to cut away some ropes so the Pequod doesn't capsize in the storm. When Ahab raises his lance after the rigging gets the Fire, the lance too glows with it and Ahab simply wipes the Fire from his lance.