Naturespeak 

Saint Elmo's Fire

A hair-raising phenomenon

By Jack Souther, Whistler Naturalists

Except for the towering cumulus clouds building on the southern horizon it started like any other July day on Blackcomb. At the top of 7th Heaven young racers and their coaches dropped down to the glacier for a day's training, and as "Mountain Host" I prepared to answer sightseers’ questions about mountains and glaciers. But that day the question was, "Why is everybody's hair standing on end!"

The cumulus clouds had grown into ominous, grumbling thunderheads. A flash of lightning – followed by thunder and a message from Dispatch on my radio: "Due to a severe electrical storm all lifts are being closed." For the next three hours it seemed like all humanity was packed, soaking wet, into the Horstman Hut while the ridge outside was lashed with hail and jolted by lightning strikes.

So why was everyone's hair standing on end? Not out of fright, but because we were caught in an intense electrical field under the negatively charged base of a cumulonimbus cloud. If it had been dark we would have seen a bluish or reddish glow surrounding our heads, and any other pointed objects. The phenomenon known as Saint Elmo's Fire occurs when an electrical discharge is intense enough to cause ionization of air molecules, similar to a neon light. It is often accompanied by an audible buzzing, and hair isn’t the only thing attracted skyward. I have watched droplets of water spitting upward from the hissing point of an ice axe.

The electrical charge is generated within the cloud by interaction between hail pellets and droplets of super-cooled water. When the two collide the water freezes to tiny, positively charged ice crystals. These are swept upward by violent updrafts leaving the larger, negatively charged hail pellets near the base. Thus the cloud itself becomes polarized, positive at the top, negative at the base. A balancing positive charge is induced on the people and other stuff beneath. The electrical field may build to several thousand volts per centimetre and ultimately lead to a stroke of lightning, either between the upper and lower parts of the cloud, or from the cloud to some pointed object on the ground.

A stroke of lightning to the ground occurs when a luminous path of ionized air projecting downward from the cloud is met by a similar path of ionized air projecting upward from the ground. When the two meet the circuit is closed and a violent surge of electrical current occurs as lightning. The updrafts that produce the charge separation can reach vertical speeds of 180 km/h and are capable of recharging the cloud within minutes, allowing a single cloud to produce repeated lightning strikes.

If there is a message in all this I guess it’s "don't mess with St. Elmo." When your hair stands up and your ice axe starts to buzz he is warning you there is a big electrical charge up there searching for a conductive pathway to the ground.

Upcoming Events:

August 4 — Monthly Bird Walk . Meet at the base of Lorimer Road at 7 a.m. Contact Michael Thompson (932-5010) for more information.

August 7 — Sunset Nature Walk . Meet in the day use parking lot at Brandywine Falls (about 15 minutes south of Whistler Creek) at 7 pm. Call Bob Brett (932-8900) for details or to arrange a ride. Free for members; $2 for non-members.

August 11 (tentative) — Perseid Meteor Shower . The best viewing window for the meteor shower is Saturday night, the 11th. Depending on interest, we may get together to view it. Call Bob Brett (932-8900) if you’re interested. Telescopes welcome.

Sightings and Memberships: NatureSpeak is prepared by the Whistler Naturalists. To become a member or to report noteworthy sightings of mammals, birds, or other species, contact Lee Edwards (905-6448; e-mail: leighe11@hotmail.com).

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