The stately advance of clouds from the ocean, and their enfolding cloudscapes in the sky, are part of the entertainment of life on the Atlantic fringe. At both ends of the day their sculpting by the sun and the astonishing, often voluptuous colours of their light – these the more intense and theatrical in the raking declinations of winter – help to make up for the periodic Sturm und Drang of the new climatic regime. It has made us passingly knowledgeable about kinds of clouds – cirrus, stratus, cumulus – if not all their permutations into altocumulus stratiformes (good for sunsets), nimbostratus (bad for snow) and so on.
One shape, however, we could well learn to dread: the piled up, darkening coiffure of Cumulonimbus capillatus, the towering thundercloud. Seen on the ocean horizon as a safely distant, anvil-headed blob of grey, or a looming flotilla thereof, one can raise a wet finger to the wind and guess at the odds. A midnight flash through the bedroom curtains has us counting five seconds to the mile as the thunderclap rolls to our ears, a ritual we are now unlikely to refine into kilometres.
But sometimes, as in the last parade of storms, a scattered thunderhead creeps up without an early rumble of warning, to discharge a sudden flash-bang to a handy hillside transformer. In that instant Ethna drew a brilliant blue arc from a light switch like the witch in The Wizard of Oz, much to her discomposure. She needed a hug and a large slug of sherry as the hail shower lashed at the windows.
It was this sort of shock that once made our beloved postmistress shy away from her switchboard and decline to plug anybody through until the sky cleared again. A friend at the foot of the mountain had her telephone blown off the wall by a lightning strike. And once a man walking the shore at Bunlach had lightning strike a brass collar stud at the back of his neck and was left with a little round burn to prove it once he’d picked himself up – or so the story goes.
Townland lore also offers the thunderbolt that tore through one thick wall of a house and out the other, tossing showers of slates in the air as it went.
Even without a direct hit on the house a lightning strike to rural power points unleashes some wicked amperes of mischief. Our desk computers are buffered by surge-absorbing batteries, but broadband systems can be vulnerable.
The aerial on our gable draws a wireless signal from Inishbofin and makes us a node for sharing it with neighbours. Restoring the flow took a mercy mission from our enterprising service provider, Lighthouse Networks, in Co Galway, and some intensive electronic microsurgery.
The arrival of the ESB, no less solicitous, both restored the pumped flow of water from our well and rescued me from another defeat in a candlelit session of Scrabble.
Climate change
Do we need to know more about thunderstorms as climate changes?
Their mention seems almost incidental in the gloomier weather forecasts, but the damage and disruption if their number and intensity increase could be real.
Some parts of large continents, like North America, already live with lightning as a frequent and routine seasonal hazard: perhaps a stormier west of Ireland will need to do the same.
A thundercloud, I learn, has a typical lifetime of about an hour. The vital trigger is a violent, upward rush of air – warm air sucked up into cold – so a warming ocean and an icy transatlantic jet stream above it seem the perfect crucible for such events.
Moisture in the rising air alternately coalesces and splits into raindrops or hail, creating positive and negative charges. The droplets are multiplied or the hailstones grow bigger by travelling up and down repeatedly within the cloud, often at great speed, until the build-up of positive charges is unleashed as millions of amperes of lightning.
Most flashes are fired within thunderclouds or dart between them – only about 20 per cent are forked lightning reaching the ground. Just as hailstones whizz up and down in the still-uncertain process of cloud electrification, the first downward discharge of lightning, typically in 50m zigs and zags, can generate return strokes – perhaps three or four in one dazzling flow of energy, lasting microseconds, that only a camera can freeze for study.
The energy in the return stroke heats the slender channel of air to more than 30,000 degrees, producing the incandescence of the flash, and expands a shock wave, heard as thunder as it travels, at a mere 350m per second, to one’s ear.
A close encounter, such as ours, produces a loud bang as brief as a tenth of a second. It just sounds like the end of the world.