ST. ELMO’S FIRE - As in nature, when a storm develops, clouds are charged due to the collisions of the atoms inside the clouds. The upper part of the cloud is positively charged while the lower part of the cloud is negatively charged. This high concentration of the negative charge at the bottom of the clouds repel the electrons in the atoms at the ground and polarizes the ground positively. As the concentration of the negative charge around the clouds gives rise to an intense electric field, the air around the region gets their electrons ripped off from them, forming a plasma zone. This also happens so that the charge separation in the clouds neutralizes in some way. Besides, this is indeed how lightning begins to form. The ionization continues to grow as long as the electric field intensity is higher. It forms a conduit of plasma (called as leaders or downward streamers) so that the electrons can flow towards the ground. In the ground, the same happens. Except the concentration of positive ions would be more concentrated at tall rods and sharp objects like a lightning rod. The air ionizes around it and it creates an upward conduit (upward streamers) at a slower rate. These conduits are plasma that is so ready to conduct electric current better than their previous phase. Therefore, when the downward conduit and the upward one meet each other, the circuit is complete and lightning strikes. If you know how a neon light works, you could figure it out yourselves.

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St. Elmo’s Fire

How St. Elmo’s Fire Works

by Karthikeyan KC 

If you have ever voyaged across the sea or flown through a thunderstorm, you might have seen a bluish glow that closely resembles a sustained spark.

It’s a phenomenon called as St. Elmo’s fire.

The name ‘St. Elmo’s fire’ is just a ridiculous historical name given to the phenomenon and it really has nothing to do with fire.

Hence, it is neither a fire nor a lightning. It is more of a static discharge.

Before we see how St. Elmo’s fire work, it is essential to do a quick review on how lightning works.

Lightning

As in nature, when a storm develops, clouds are charged due to the collisions of the atoms inside the clouds.

The upper part of the cloud is positively charged while the lower part of the cloud is negatively charged.

This high concentration of the negative charge at the bottom of the clouds repel the electrons in the atoms at the ground and polarizes the ground positively.

As the concentration of the negative charge around the clouds gives rise to an intense electric field, the air around the region gets their electrons ripped off from them, forming a plasma zone.

This also happens so that the charge separation in the clouds neutralizes in some way.

Besides, this is indeed how lightning begins to form.

The ionization continues to grow as long as the electric field intensity is higher.

It forms a conduit of plasma (called as leaders or downward streamers) so that the electrons can flow towards the ground.

In the ground, the same happens. Except the concentration of positive ions would be more concentrated at tall rods and sharp objects like a lightning rod.

The air ionizes around it and it creates an upward conduit (upward streamers) at a slower rate.

These conduits are plasma that is so ready to conduct electric current better than their previous phase.

Therefore, when the downward conduit and the upward one meet each other, the circuit is complete and lightning strikes.

St. Elmo’s fire

Now that you know how lightning works, explaining the St. Elmo’s fire phenomenon is quite easy.

Besides, if you know how a neon light works, you could figure it out yourselves.

On the ground, during a thunderstorm, say a mast of the ship, a tall post of any house, or even the sharp corners of any structure, acts as a possible lightning rod.

A tall pointed structure with reduced surface area gives the lightning a chance to discharge with a less resistive path to the ground.

What does it have to do with the St. Elmo’s fire phenomenon?

Well, the way lightning rod works is that it ionizes the air around it, as its positive polarity attracts (tears) the electrons off the atoms whose protons are already being attracted by the negatively charged clouds (and repelled at the same time by the lightning rod).

This ionization tries to neutralize the cloud at the bottom.

However, under certain conditions, when the charge density is higher in the clouds, an equal higher density of positive charge on the earth front is created and even higher positive ions accumulate at the tall objects like the lightning rods or masts of the ships.

Therefore, this very high electric potential difference ionizes the air in a slightly different way.

As the voltage is too high, the energy of the free electrons is so high around the pointed objects that it makes them collide with other neighboring atoms and rip their electrons further.

When electrons with higher energy recombine with the positive ions and return to a lower energy state, this produces a visible corona around the object, which possibly luminesces the plasma.

The color of the corona is governed by the atmospheric contents.

In our case of Earth, it’s primarily Oxygen and Nitrogen. Hence the blue colors.

This sustained corona discharge (St. Elmo’s fire) would continue producing this luminous plasma with a hissing sound as long as the electric potential difference between the clouds and the earth is greater than 1000 – 30,000 volts per centimeter, which is the required voltage for our atmospheric air to produce this kind of discharge.

When you see one such glow around some tall posts or objects, there is a very high probability that a lightning (arc discharge) is about to strike.

Sometimes, this faint corona is observed around the pointy horns of some animals.

Besides animals, this is more commonly observed in the wing tips and the nose of an airplane flying through the clouds.

AvatarKarthikeyan KC

Aeronautical engineer, dev, science fiction author, gamer, and an explorer. I am the creator of Geekswipe. I love writing about physics and astronomy. I am now creating Swyde.

https://geekswipe.net/science/physics/how-st-elmos-fire-works/

ST. ELMO'S FIRE - St. Elmo's Fire is a weather phenomenon involving a gap in electrical charge. It's like lightning, but not quite. Early observers of the phenomenon, mostly sailors on high seas during thunderstorms, seem to have understood they weren't looking at actual fire, because instead of abandoning ship, they took comfort in the sudden glow atop the masts. Like lightning, St. Elmo's Fire is plasma, or ionized air that emits a glow. But while lightning is the movement of electricity from a charged cloud to the ground, St. Elmo's Fire is simply sparking, something like a shot of electrons into the air. It's a corona discharge, and it occurs when there is a significant imbalance in electrical charge, causing molecules to tear apart, sometimes resulting in a slight hissing sound.

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St. Elmo's Fire

What is St. Elmo's Fire?

BY JULIA LAYTON

 

If you were to look outside your home during a thu­nderstorm and see a tall streetlamp glowing with­ blue flames, you might be tempted to call the fire department.

Then you might notice that the streetlamp is on fire but isn't actually burning -- and the water from the fire hose isn't putting out the flames.

At this point, you might be about ready to call a priest, but that, like the call to the fire department, would be unnecessary.

The phenomenon you're witnessing is actually St. Elmo's Fire. (Which has nothing to do with a 1980s coming-of-age film starring a young Emilio Estevez.)

St. Elmo's Fire is a weather phenomenon involving a gap in electrical charge.

It's like lightning, but not quite.

And while it has been mistaken for ball lightning, it's not that, either -- and it's definitely not fire.

Early observers of the phenomenon, mostly sailors on high seas during thunderstorms, seem to have understood they weren't looking at actual fire, because instead of abandoning ship, they took comfort in the sudden glow atop the masts.

Such famous figures as Magellan, Caesar and Columbus experienced St. Elmo's Fire on their journeys.

And Pliny the Elder, who seems to have documented absolutely every natural phenomenon back in the 1st century A.D., beat everyone else to the punch when he described blue flames appearing out of nowhere during thunderstorms.

Sailors tended to attribute the glow to "St. Elmo," a mispronunciation of St. Ermo or St. Erasmus, the patron saint of Mediterranean sailors.

They believed the fire was a sign of salvation from the saint, since the phenomenon occurs most often toward the end of a storm.

Benjamin Franklin and Charles Darwin viewed the weather event through a decidedly more scientific perspective. But regardless of interpretation, it's clear they were all observing the same phenomenon. And contrary to popular belief, St. Elmo's Fire doesn't only occur at sea.

As with all electrical phenomena, St. Elmo's Fire is about electrons. So, what is St. Elmo's Fire if it's not a form of lightning? Find out in the next section.

Causes of St. Elmo's Fire: The Fire That's Not a Fire

Like lightning, St. Elmo's Fire is plasma, or ionized air that emits a glow.

But while lightning is the movement of electricity from a charged cloud to the ground, St. Elmo's Fire is simply sparking, something like a shot of electrons into the air.

It's a corona discharge, and it occurs when there is a significant imbalance in electrical charge, causing molecules to tear apart, sometimes resulting in a slight hissing sound.

The first step in generating St. Elmo's Fire is a thunderstorm.

As you can learn in How Lightning Works, a thunderstorm creates an electrically charged atmosphere.

There is a charge difference between the storm clouds and the ground, and this difference creates voltage, or electrical pressure.

In between the clouds and the ground, the atoms in the air undergo changes; most important to our discussion, electrons move farther away from protons, creating an environment that allows electrons to move around freely. In other words, the air becomes a good conductor.

Once the air is conducive to the movement of electrons, those electrons continue to increase the distance between their positively charged counterpart, protons.

This is ionization, and plasma is simply ionized air.

The phenomenon that causes St. Elmo's Fire is a dramatic difference in charge between the air and a charged object, like the mast of a ship, the tip of an airplane wing or the 30-foot steeple of a church -- things we often think of as potential lightning rods.

When the voltage gets high enough, usually around 30,000 volts per centimeter of space, the charged object will discharge its electrical energy [source: Scientific American].

The reason why St. Elmo's Fire occurs most often on pointed objects is that a tapered surface will discharge at a lower voltage level. The tip of a steeple, mast or airplane wing presents something like a condensed surface charge.

When the air molecules tear apart, they emit light.

In the case of St. Elmo's Fire, the discharge is continuous -- sometimes lasting several minutes -- and creates a constant glow.

The glow is blue because different gasses glow different colors when they become plasmas. 

Earth’s atmosphere has nitrogen and oxygen in it, and this particular combination happens to glow blue.

St. Elmo's Fire is exactly what's happening in neon tubes -- essentially a continuous spark.

If Earth's atmosphere were made up of neon, St. Elmo's Fire would glow orange instead of blue.

A neon tube is simply St. Elmo's Fire contained in glass.

St. Elmo's Fire also behaves something like a plasma globe.

One pilot described the phenomenon occurring on the windshield of her small plane while flying through a storm cloud; when she touched the inside of the windshield, blue streaks reached toward the tips of her fingers [source: USA Today].

BALL LIGHTNING

St. Elmo's Fire and "ball lightning" are two different things.

The scientific community can't agree on what ball lightning is, but it's definitely not St. Elmo's Fire.

Ball lightning can float around the air, while St. Elmo's Fire stays put.

https://science.howstuffworks.com/nature/climate-weather/atmospheric/st-elmo-fire.htm