Archive for the ‘Meteorology’ Category

The Cloud Book: How to Understand the Skies, Richard Hamblyn (David & Charles 2008)

If the best things in life are free, then clouds are high on the list. The sky is a giant book opened every morning and written with the story of the weather. The story can be can be beautiful, dramatic, awe-inspiring. Or dull, dreary, depressing. It’s both history and prophecy, describing what the weather has been and what it will be. Humans have been staring up at the story for millions of years, but the symbols in which it’s written weren’t made clear until very recently:
The Cloud Book by Richard Hamblyn

…in contrast to all other earthly phenomena, from microbes and minerals to the greatest plants and animals, all of which have been classified and reclassified many times over since early antiquity, clouds (at least in Western culture) remained uncatalogued and unnamed until the early nineteenth century when the Latin terms that are now in use – “cirrus”, “stratus”, “cumulus” and their compounds – were bestowed on them by Luke Howard (1772-1864), an amateur meteorologist from East London. (Introduction, pg. 9)

Precise description is an essential part of science, because it allows you to compare, contrast and classify. What the Swedish biologist Linnaeus had done for the relatively stable world of animals and plants, Howard did for the ever-shifting world of aerial vapour. Indeed, clouds are divided like living creatures into genera, species and varieties, all falling under three broad categories: low clouds, medium clouds and high clouds. So the size and complexity of the names can echo the size and complexity of the clouds themselves, like “Cirrus spissatus cumulonimbogenitus”, whose specification is “Dense cirrus, often in the form of an anvil, being the remains of the upper parts of a cumulonimbus cloud” (pg. 90). It has a code, CH3, a symbol (see table for examples) and an abbreviation, Ci spi cbgen.

So this book is an introduction to serious meteorology, but it’s full of beauty too. Howard’s science inspired and informed the art of painters like Constable and poets like Goethe and Shelley. All three men would have marvelled at the photographs here, which capture clouds from all around the world: CL5, Stratocumulus stratiformis is “dark, rolling layers of cloud” over “Oslofjord, Norway” (pg. 36); CM9 is “a chaotic sky over Bracknell in Berkshire” (pg. 80); and the CH3 mentioned above is “seen from Grande Anse Beach, Grenada” (pg. 90). But most of the named photos were taken somewhere in Britain: fluffy white cumulus humilis over the “Vale of Evesham, Worcestershire” (pg. 22); mottled and marching altocumulus stratiformis over “Ebbw Vale, Gwent” (pg. 68); white and wave-like altocumulus stratiformis duplicatus over “Mallaig, Scottish Highlands” (pg. 74); a “rare” cirrocumulus lenticularis against blue sky over “Painswick, Gloucestershire” (pg. 106). Most of the unnamed photos are presumably British too.

Modern geology got its start in Britain because rocks are so varied here. Perhaps modern meteorology got its start here for the same reason. Some climates are stable for months at a time. British weather can change from minute to minute, but, as James Bond muses in Live And Let Die (1954), England at least is also a country where you can take a walk every day of the year. This book is an excellent way to train your eyes for what you see when you look up. It also describes what you might see on a walk at night:

Appearing as thin, milky-blue or silvery waves high in the sky, on the fringes of space, NLCs [noctilucent clouds] look as mysterious as they in fact are: they remain the least understood clouds of all, the mechanics of their formation in such dry, clear, intensely cold conditions (-125ºC/-193ºF) having not yet been discovered, although many hypotheses have been advanced, including the idea that they seed themselves from meteorite debris, from dust blasted high into the atmosphere by major volcanic eruptions, or even from the constituent elements of space shuttle exhaust fumes. (“Noctilucent clouds”, pg. 121)

That’s in “Part 2” of the book, devoted to “Other Clouds and Effects”, like sun-pillars, coronae, halos, parhelia, crepuscular rays, contrails, Kelvin-Helmholtz waves, glories, lightning and rainbows. I haven’t seen all of those, but I saw a circumzenithal arc recently – “a band of bright prismatic colours” produced by sunlight refracting through “horizontally aligned cirriform ice-crystals” and resembling an “inverted rainbow” (pg. 131). I noted that it was directly overhead, but didn’t realize that it had to be so. Nor did I think that the time of day was important:

Typically a quarter-circle in shape, its colours, which are often brighter than those of the rainbow, run from blue near the zenith, down to red near the horizon. Due to the precise angle in which the refracted light exits the sides of the horizontal ice-crystals, CZAs cannot occur if the sun is more than 32.2º above the horizon, and the brightest arcs of all – which the cloud-writer Gavin Pretor-Pinney has archly dubbed the “cloud smile” – occur when the sun is exactly 22º above the horizon. (“Circumzenithal arc”, pg. 131)

So mathematics is obvious there, but it’s present everywhere in meteorology: clouds seem chaotic, but relatively simple rules underlie their formation and evolution. It’s just that there are a lot of continuous variables: temperature, humidity and so on. So complexity arises from simplicity. This book classifies and catalogues the chaos of complexity, explaining the why and where of one of the best and most beautiful things in life.

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