Crystalline clouds

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Sunshine and cloud are traditional opposites. Yet droplets make up only about 10 p.p.m. of a cloud's volume — why does sunlight not go straight through? Sadly, a photon traversing a random array of droplets is almost certain to hit one sooner or later, and be scattered. So, says Daedalus, make the array non-random.

He recalls Faraday's use of iron filings to map a magnetic field. Each iron particle has a magnetic dipole induced in it in the local field direction. Axially arranged dipoles attract one another, and align themselves into chains along the lines of force. Equatorially arranged dipoles repel one another, so each chain spaces itself as far as possible from its neighbours.

The same principle must apply to electrostatic fields. A dielectric particle (such as a water droplet) must have an electric dipole induced in it by a local electric field. The dipoles will align themselves into parallel chains following that field. So, says Daedalus, put a cloud in an electric field whose lines of force point at the Sun, and its droplets will form parallel chains pointing the same way. Sunlight will pour down unimpeded between the chains, and the cloud will become almost perfectly transparent in that direction.

At first Daedalus envisaged some mighty system of captive balloons supporting charged wires, their positions constantly adjusted to keep the field pointing at the Sun. But he soon realized that a radio beam would do just as well — provided it was polarized to point its electric vector at the Sun. Even if its field reversed at many megahertz, the dipoles it induced in the droplets would still follow it perfectly.

DREADCO's weather-brightener will launch an intense radio signal into the cloud deck. It will be constantly adjusted to keep the signal polarized in the Sun's direction. A watcher anywhere beneath the cloud will see a hole in it, through which the Sun will beam down on him. The rest of the sky will still appear cloudy; yet, oddly, the landscape will be uniformly bright. The DREADCO weather-brightener will transform tourism. British seaside resorts and holiday towns will queue up to install this answer to their Mediterranean and tropical rivals. Even those rivals may install it, though for a converse reason. By aligning its signal at 90° to the solar direction, the thinnest cloud might be made opaque enough to screen out the scorching midday Sun.

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