Among all the music the weather makes, thunder is arguably the most dramatic. To the ancients it sounded like the Gods knocking down the door, come to deal to human misbehaviour or maybe warring amongst themselves.
For the Greeks it was the sound of Zeus’s thunderbolts; to the Vikings the sound of Thor’s hammer; to the ancient Sumerians the bellowing of the bull of Adad, the weather god; and to the Plains Indians, the beating of the wings of the giant thunderbird.
The temperature of a lightning bolt has been measured at around 30,000°C and we now attribute thunder to the explosive expansion of air heated instantaneously as the lightning bolt passes. Although the electric current only takes a fraction of a second to reach the ground, the sound of thunder typically lasts many seconds.
The long roll of sound is a consequence of the fact that the lightning stretches a long way up inside a thunderstorm cloud. So, while you may only be a few kilometres from where the lightning strikes the ground, you may be twice as far away from where the lightning starts, high up in the cloud. This also explains why a clap of thunder starts loud then tails off as the sound from the top of the lightning bolt has dissipated more in its longer journey.
Nor is thunder the only sound that lightning can make. People close to the strike often report hearing a loud hissing sound just as the lightning hits.
If thunder is the most dramatic weather sound, perhaps the most terrifying is the roar of a tornado—often likened to the sound of a freight train hurtling through the sky. At their worst tornados have wind speeds in excess of 500 km/h and can lift railway engines off the ground as well as obliterate buildings. These extreme winds are caused by the large difference in air pressure between the inside and outside of a tornado. This was finally measured a couple of years ago when a pressure sensor was placed in the path of a tornado. Just 84 seconds after the sensor was left on the ground it recorded a pressure drop of over 100hPa as the tornado went over. The pressure change was concentrated in a few tens of metres across the eye-wall making a pressure gradient much more intense than that of a hurricane.
In New Zealand, most people never see a tornado, let alone hear one, but most of us are familiar with the roar of a gale. The wind is at its most musical when it has something to play with—pine trees for example. I was enchanted, as a child, when my father told me that the sound of the wind running through the tall pines on the farm where he grew up was known as the “soughing” of the wind. I looked the word up in the dictionary recently, hoping to find that it was ancient and restricted to that usage but was disappointed to find that it had a plethora of more mundane meanings.
Aside from trees, buildings also provide the wind with something to gnaw on. In a country that has done so much with corrugated iron, it is not surprising that the wind has found the iron especially useful for making noises. As Allen Curnow writes in his iconic poem:
“Wild with the iron that tears at the nail And the foundering shriek of the gale.”
Flags and washing flap and crack like dull whips, and nowadays there is that agitated tinkling when you pass marinas as the ropes slap against the metal masts of the yachts.
The waves that the wind makes on water carry latent music–packets of sound the wind sends thousands of miles across the oceans, like so many wet hands to smack the drum of a beach, sometimes soft and soothing, sometimes loud and threatening.
During the cyclone of February 1936 the sound of the waves breaking in Cloudy Bay was so loud it was heard as far inland as Blenheim.
Rain also makes a rich music on the various surfaces it falls on, be it tin roofs, glass windows, concrete paths, trees or leaves. I was particularly taken with a phrase I read years ago where a novelist described ” a gentle rain with mercy on its mind.” In fact, I found out recently that villagers in Iran and Turkey use the same word for rain and mercy. Then there are the various noises of moving water from the tinkle of a steep mountain stream to the roar of a flood. And, once heard, who can ever forget the eerie sound of boulders knocking together under water as they are rolled downstream by a mountain river in full spate.
Frozen precipitation has its own special music, from the rattle and clatter of hail, varying with its size and fall speed, to the magical silence of falling snow. Once on the ground, there is the squeak of fresh snow as your feet sink into it. Glaciers creak and groan as they grind slowly over bedrock, then crash as ice calves off the front end, while little can match the terrible roar of a large avalanche.
In fine weather, the sun joins the meteorological orchestra, heating rocks until they crack open in sudden small explosions, or trigger the larger clatter of rock falls. And what have we humans done about all this music? Great mimics that we are, we have made music right back, using drums and bullroarers to summon the rain gods to break droughts.
Now we even put musical opportunities in the wind’s path when we hang wind chimes from veranda porches or build wind harps. In Catalonia, Spain, there is even a giant wind organ constructed to a design left by Salvador Dali. The organ can only be played when a gale force Tramontana pours down off the Pyrenees much like a Canterbury Nor’wester pounding down from the Southern Alps.