Clouds and the War

As the devil said to Noah, "It's bound to clear up."--Anon.

As every airman knows, it is also sometimes bound to get cloudy--a fact that has saved and cost many combat flyers' lives. Because clouds are one of the important military concerns of World War II,* scientists have recently taken to more intensive cloud-gazing. Last week an unusually lucid explanation of the function of clouds in war was presented by an old cloud man, William J. Humphreys (retired) of the U.S. Weather Bureau, in a new book, Fog, Clouds and Aviation (Williams & Wilkins; $3).

What Are They? Scientists know surprisingly little about clouds, which were not even named or classified until 1803 (by an English druggist named Luke Howard). They know how clouds and fogs (clouds on the ground) are formed--by the cooling of humid air, which condenses water vapor on particles of dust, pollen or soot in the air. They also know what a cloud or fog is made of--water droplets (or ice crystals) so small that an 1,800-cu. ft. block of dense fog contains only one-seventh of a glass of water. But many questions, such as what makes a cloud turn to rain, or how a rainbow is formed, are still subjects of vaporous debate.

How to Use Them. From scientific observation and airmen's experience, Dr. Humphreys has compiled many useful hints for flyers:

> Clouds have general upper and lower limits/-: in middle latitudes the highest clouds are six or seven miles above sea level (because air gets no colder above that height); the lowest (except for fogs) are at about 2,000 ft. In thickness, a cloud may vary from a wafer (cirrus) to several miles (cumulonimbus).

> Of the many kinds of fog--dry, wet, sea, land, smog (smoky), black (sooty), ice, pea-soup (moderately smoky, yellowish, once thought peculiar to London)--most are not troublesome to flyers because they are shallow or ephemeral. But there is great danger in advection fogs, produced by the drifting of warm air over cold land or water or snow banks (common off Labrador): they are deep--sometimes thousands of feet--and treacherous.

> The high, thin, wispy cirrus cloud and its relatives, the milky cirrostratus and ripply cirrocumulus, are ideal cover for high-altitude bombers: they provide a one-way screen that allows an airman to see his target but hides him from planes or groundlings below.

> Altostratus, a high, flat, greyish blanket, gives a flyer a wide range of maneuver: he can duck below it to look at the ground, climb above to hide, thread his way above and below to lose a pursuer.

> Most helpful clouds are the woolly, lumpy cumulus and its relatives--the high stratocumulus (bumpy) and altocumulus. These rich vapors are excellent for playing hide-&-seek with enemy planes, give a fighter cover for sudden dodges and quick surprises. Because the cumulus frequently hovers over islands, it often shows a flyer where land is when he cannot see the land itself. It also shows glider pilots where rising air currents are.

> Most dangerous are the low, dark nimbostratus (because of its poor visibility and the danger of icing) and the stormy thunderhead, cumulonimbus. Also to be avoided: the wavy, handsome billow cloud--which gives a very billowy ride.

> Clouds as weather forecasters: thin cirrus clouds or altocumuli mean fair weather for at least 24 hours ("the higher the clouds, the finer the weather"); thickening cirrus and layers of clouds moving in different directions mean rain; big cumulus clouds in the morning mean thunder showers in the afternoon; persisting fog means rain by afternoon or night.

*The Army, which already has thousands of meteorologists, is campaigning to recruit and train over 10,000 more.

/- The U.S. Weather Bureau has just developed a photoelectric instrument, using a vertical beam of light and a phototube scanning the beam, which quickly measures cloud heights day or night by triangulation.

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