"I pass my whole life," complains Mr Jarvis Lorry of Tellson's Bank, "in turning an immense pecuniary mangle." Meteorologists, with a singularity of mind not dissimilar to that of Dickens's character, devote their working lives to chasing vortices, and to unravelling the transient mysteries of ephemeral whirlpools.
Loosely speaking, a vortex is anything that whirls around - a whirlpool, a whirlwind, or even a cup of coffee, freshly stirred. Atmospheric vortices are the raw material of meteorology. The atmosphere is a vast jigsaw puzzle of these interdependent swirls of air, all superimposed on one another in a symbiotic chain of nearchaotic destiny. Indeed one whimsical meteorologist, Lewis Fry Richardson, summed up our celestial laboratory in rhyme three-quarters of a century ago:
Great whirls have little whirls,
That feed on their velocity;
And little whirls have smaller
whirls And so on to viscosity.
The large-scale motion of the atmosphere, which we call the general circulation, is itself a kind of vortex, moving as it does from west to east in perpetual circumglobal motion. A facet of it has come to prominence in recent years as the circumpolar vortex, a semi-permanent band of strong winds at high latitudes which traps the frozen polar air within it, bringing about conditions which, with a little help from CFCs, destroy our stratospheric ozone.
Superimposed on the general circulation are the familiar depressions of the middle latitudes. They vary from a few hundred to several thousand miles across, and have a lifetime of about a week. On a smaller scale, but much more vicious, is the cyclone - alias "typhoon" or "hurricane". And smaller still, the average tornado is only a hundred yards or so in diameter, and has a lifetime of an hour or less.
Nearly all these swirls of wind have something else in common besides the whirling motion that makes them what they are: in the northern hemisphere, they rotate in an anticlockwise sense. Even tornadoes, the smallest, albeit the most vicious on the list, nearly always twist against the clock, although there have been a few instances of tornadoes which appear to have rotated clockwise.
More gentle, tiny vortices are also present in the air, and because of their smaller scale they are free to rotate in any sense they please. Many of the constant swirls and eddies of a turbulent wind are vortices, and even in conditions that seem to us completely calm, tiny whirls of air are caused by the movement of a blade of grass, or even by that proverbial progenitor of modern hurricanes, "the flap of a butterfly's wing".