Wednesday, September 29, 2010 9/29/10 - clouds

In today's excerpt - clouds and the names of clouds:

"The person most frequently identified as the father of modern meteorology was an English pharmacist named Luke Howard, who came to prominence at the beginning of the nineteenth century. Howard is chiefly remembered now for giving cloud types their names in 1803. ...

"Howard divided clouds into three groups: stratus for the layered clouds, cumulus for the fluffy ones (the word means 'heaped' in Latin), and cirrus (meaning 'curled') for the high, thin feathery formations that generally presage colder weather. To these he subsequently added a fourth term, nimbus (from the Latin for 'cloud'), for a rain cloud. The beauty of Howard's system was that the basic components could be freely recombined to describe every shape and size of passing cloud - stratocumulus, cirrostratus, cumulocongestus, and so on. It was an immediate hit, and not just in England. The poet Johann von Goethe in Germany was so taken with the system that he dedicated four poems to Howard.

"Howard's system has been much added to over the years, so much so
that the encyclopedic if little read International Cloud Atlas runs to two volumes, but interestingly virtually all the post-Howard cloud types - mammatus, pileus, nebulosis, spissatus, floccus, and mediocris are a
sampling - have never caught on with anyone outside meteorology and not terribly much there, I'm told. Incidentally, the first, much thinner edition of that atlas, produced in 1896, divided clouds into ten basic types, of which the plumpest and most cushiony-looking was number nine, cumulonimbus.* That seems to have been the source of the expression 'to be on cloud nine.'

"For all the heft and fury of the occasional anvil-headed storm cloud, the average cloud is actually a benign and surprisingly insubstantial thing. A fluffy summer cumulus several hundred yards to a side may contain no more than twenty-five or thirty gallons of water - 'about enough to fill a bathtub,' as James Trefil has noted. You can get some sense of the immaterial quality of clouds by strolling through fog - which is, after all, nothing more than a cloud that lacks the will to fly. To quote Trefil again: 'If you walk 100 yards through a typical fog, you will come into contact with only about half a cubic inch of water - not enough to give you a decent drink.' In consequence, clouds are not great reservoirs of water. Only about 0.035 percent of the Earth's fresh water is floating around above us at any moment.

" *If you have ever been struck by how beautifully crisp and well defined the edges of cumulus clouds tend to be, while other clouds are more blurry, the explanation is that in a cumulus cloud there is a pronounced boundary between the moist interior of the cloud and the dry air beyond it. Any water molecule that strays beyond the edge of the cloud is immediately zapped by the dry air beyond, allowing the cloud to keep its fine edge. Much higher cirrus clouds are composed of ice, and the zone between the edge of the cloud and the air beyond is not so clearly delineated, which is why they tend to be blurry at the edges."

Author: Bill Bryson
Title: A Short History of Nearly Everything
Publisher: Broadway
Date: Copyright 2003 by Bill Bryson
Pages: 263-265


Post a Comment

<< Home