Clouds

Clouds are the mountains of the sky. They can, indeed, be taller than any mountains of the earth, reaching up to 40,000 feet or, rarely, even to 60,000 feet, far beyond Everest. On the other hand, they exist on a vastly different time scale. The tallest clouds can develop and disappear in less than a day, while earthly mountains grow and erode over millions of years. In Los Angeles, there is usually not much to be seen in the way of interesting clouds. Much of the weather is simply clear, and in the spring and summer a marine layer of fog and stratus clouds moves in. Occasionally in the summer, thunderheads develop over the San Gabriel mountains and the storms may, though sometimes not for several years, move over the Los Angeles basin. Winter storms off the Pacific, usually lasting no more than a day or two, are responsible for most of the average rainfall of 15 inches. Growing up in Los Angeles, I didn't feel like I saw much in the way of cloud variety until I lived in New Mexico, Lebanon, Hawaii, and Texas. New Mexico was especially noteworthy for the colors that would play on the clouds: The setting sun could fill the same sky with yellow, pink, orange, and cherry red on different clouds. In Hawaii, where clouds would build up over the windward mountains daily in the rainy season, one striking memory is of the full moon shining on the towering, isolated thunderheads. There was, however, limited thunder from those clouds, which would drop some rain in the valleys and foothills and then disperse, often not even getting Waikiki wet. More violent weather came with the occasional winter storm (a "kona" storm, since the wind may blow from leeward, against the trade winds), or with the rare hurricane.

Clouds are classified by form and by altitude.

The basic forms, with symbols, are ("heaped up," in Latin), ("spread out," the neuter form of which is stratum, used for extensive layers of similar rock in geology), and ("lock" or "curl" of hair). Cumulus clouds tend to form from rising air, from 6,000 feet on up, and so are classified as "vertically developing" clouds. Stratus clouds, below 8,000 feet, may be rather like an elevated fog bank; or, altenatively, fog can be thought of as a stratus cloud at ground level. While cumulus clouds mean that air has risen to an elevation where the temperature is at the dew point, so that the water condenses, with stratus clouds the temperature of the air itself may have fallen to the dew point. Cirrus clouds are ice crystals at high altitude, from 18,000 to 40,000 feet; their whispy structure comes from scattering by the wind.

Besides stratus, low level clouds can include (between 3,000 and 10,000 feet), from which rain falls (nimbus simply means "cloud," or "raincloud") and (below 8,000 feet), where cumulus clouds stretch out in a solid layer, showing a lot more structure than stratus clouds, whose outlines can be very indistinct.

At high altitudes (18,000 to 40,000), cirrus clouds can form a fairly solid layer, becoming , or they can take on a lumpy structure, with grains or ripples (a "mackerel sky"), suggestive of cumulus clouds, becoming .

At middle altitudes, from 6,000 to 18,000 feet, too low to freeze into cirrus but higher than ordinary stratus, are (above 15,000 feet) and . The "alto-" element is from Latin "altus," which originally meant "grown" but came also to mean "high," as it is used in these names. Altocumulus can be part of the development of cumulus and cumulonimbus clouds.

The highest -- all the way up to 60,000 feet -- most spectacular, and most violent clouds result when the air, rising to form cumulus clouds, continues to rise, drawing moisture to high altitudes and generating extreme conditions. This makes a cumulonimbus cloud. The swelling top spreads out into a characteristic anvil shape, which then may be blown away by high level winds. Because of freezing air at those altitudes, the streaming clouds from the anvil will often take a cirrus form. Freezing air can also cause hail to form, as ice crystals begin to fall and then are lifted back up again and again to grow larger and larger. When the hail finally falls, descriptions of its size are borrowed from the produce counter and from sports: Small hail is described as "pea" sized, whence we move up to "grape" sized, "ping-pong ball" sized, "golf ball" sized, "baseball" sized, and, most devastating of all, "grapefruit" sized. Baseball and grapefruit sized hail can break any window, ruin a car, flatten a field of crops, or even kill somebody. The movement of wind, water, and ice up and down the column of clouds also generates differentials in electrical charge, which are then discharged as lightning. Isolated thunderstorms, generated by summer heating, may pass over with a minimum of damage. Spring cold fronts, however, pushing still cold air from the north under warm moist Gulf air, as in Texas, can produce massive squall lines of thunderstorms, stretching for hundreds of miles, filling the sky with vast gray clouds, rain, wind, hail, lightning, and, worst of all, tornadoes. These conditions get called, with charming understatement, "severe weather." Short of hurricane force winds, or actual tornadoes, nature provides no more awesome weather. During one overnight thunderstorm and flash flood that I witnessed in Austin, Texas, on the eve of Memorial Day in 1981, where serious flooding and deaths occurred, the flashes of lightning were so frequent that they were right on top of each other and the night was literally without darkness.

I also see other cloud symbols, such as the altostratus plus cirrus symbol at left. I have yet to see exactly what this would look like in the sky, but I like how this looks.



The Beaufort Wind Force Scale, The Saffir/Simpson Hurricane Scale, & the Fujita Scale of Tornado Intensity

Note on Dew Point

Snow, Sleet, Ice, and Rain

Philosophy of Science

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