Balloons for the Jet Stream

A wily Japanese tactic in World War II was to launch balloons carrying small explosive or incendiary bombs in the hope that they would drift across the Pacific and land in the U.S. Some of them actually did land in the Pacific Northwest, and although they caused almost no damage, they proved that the westerly winds at high altitude are fine balloon carriers. Last week the U.S. Navy was following the Japanese lead by launching balloons of plastic film from Oppama, Japan. Instead of bombs the balloons carried instruments to report weather conditions encountered on their long voyages.

The Navy's balloons are helium-filled and 39 ft. in diameter. Besides their instruments they carry a 50-watt battery-powered radio transmitter that broadcasts on three frequencies* and can be monitored and tracked by ground stations.

Each balloon also carries 350 lbs. of iron shot for ballast. The balloon is designed to float at the altitude (about 30,000 ft.) where air pressure is 300 millibars. When it loses buoyancy as helium escapes, an automatic device dumps a little ballast and keeps it from descending. When all the ballast is gone, the balloon eventually sinks, and another automatic device cuts the instrument gondola free and lowers it to earth on a parachute. Instructions on the gondola urge finders to send it to the Navy's research laboratory, but even if the instruments are not recovered, it makes little difference. The balloon will have been tracked all along its flight, and its instruments will have reported faithfully by radio. The main reason for recovering the instruments is to check on any that failed.

The first balloon launched fell in the Pacific near the U.S. West Coast. The second followed a sinuous course, cruising southeast from Japan, passing south of Midway Island, then veering north to pass 900 miles north of Hawaii. It entered the U.S. near the Oregon-California boundary and finally landed near Jackson, Miss. The whole trip (roughly 10,000 miles) took three days and two hours. The balloon's maximum speed when pushed by the high-altitude jet stream was 200 m.p.h. The third balloon cannot be located because of instrument failure, but the next four were launched successfully. When last reported, they were spread out between Japan and north-central Canada.

The Navy does not expect all its balloons to land in the U.S. Many will go down in the Atlantic from Labrador to Cuba. They will range en route as far north as Alaska and as far south as Hawaii. Wherever they wander, they will report winds, temperature and air pressure in regions almost unknown to meteorologists, and will give better understanding of the high-speed winds that dominate the airways where jet liners will soon be flying.

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Astronomers at the University of Pennsylvania have another and less direct method for observing winds at high altitude. The twinkling of stars, which so annoys astronomers, is due to turbulence in the atmosphere. Therefore, the twinkling should yield information about the currents that stir up the turbulence, even when they cannot be measured directly in any other way.

Backed by Air Force money, Drs. William M. Protheroe and William Blitzstein are recording star-twinkle and comparing its frequency and intensity with winds that are known to be blowing aloft. They hope that when they have gained enough experience, they can look at the stars and tell by their twinkling how the high winds are blowing.

* For interested hams: 7,000, 11,000 and 18,000 kc.

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