Kites and Meteorology

from Physics in Canada

Kite-flying and meteorology have a close relationship. The ability of a kite to fly depends on the meteorological conditions, and kites themselves have played a key role in the development of modern day meteorology.

Alexander Wilson a Scotsman, was the first to use kites for meteorological purposes. He flew a series of kites in train to measure upper air temperatures. The kites were from 1 m to 2 m in length. To obtain information, he released thermometers with bushy tassels of paper tied to them from some of the higher kites.

Around 1840, Espy, an American meteorologist, used kites flown by the Franklin Kite Club to determine cloud base height of convective clouds. He was then able to relate these heights to the surface temperature and dewpoint. From this came the first estimate of the temperature lapse rate in convective conditions. For the first time, updrafts were detected below cloud bases.

But it was E. D. Archibald, a British meteorologist, who is credited with initiating the kite as a serious meteorological tool. - a use that continued into the 1930s. In 1883, he established that kites were superior to balloons for some purposes. His principle object was to measure the increase in wind velocity with increasing elevation. He was the first to use piano wire for the flying line.

Archibald's original kites were of the conventional diamond type, with tails, and were made of silk and bamboo. They were flown in tandem. At various points on the wire Archibald attached four self-recording anemometers, weighing 0.7 kg each. He reached heights ranging from 60 m to 500 m. In 1886 he was the first to take aerial photographs from a camera that was carried aloft by a kite.

Archibald's work was followed up by efforts of many organizations in the United States and Europe. One of the most prominent was the Blue Hill Observatory near Harvard. In 1894 William A. Eddy, a journalist and kite designer from New York, came to Blue Hill for the purpose of lifting instruments into the lower atmosphere with his kites. A lightweight thermograph weighting 1.1 kg was constructed with a basket placed over the instrument to screen the sensor from radiation.

On August 4, 1894, using a series of five Malay tailless kites, the thermograph was carried aloft to an altitude of 427 m, as measured by optical theodolites 100 m apart. The 4 hr continuous recording of temperature obtained from this flight was the first of its kind in the world, marking the start of worldwide pressure, humidity, and sometimes wind soundings of the atmosphere.

Improvements in techniques quickly followed. In 1895 a meteograph was developed that could measure pressure, temperature and wind speed. Twenty-eight flights were made that year, the highest ascent being to 567 m. The late 1800s saw two important improvements that dramatically increased the maximum height and reliability of the kites.

In 1896 piano wire was adopted for the kite line. At this time, the winch, a hand cranked reel mounted on a wheelbarrow, had devices attached to it to measure the amount reeled out, the inclination of the wire, and the amount of pull on the line. The highest flight that year was 2651 m.

In 1897 the second advancement was the development of a mechanized winch. A two-horsepower kerosene-fired steam engine was developed to drive it. The wire was first wound around a strain pulley thus avoiding the tremendous compressional forces that built up on reels, and then onto the storage reel. Oil was automatically dropped onto the wire to prevent rust.

In 1897 a meteograph was raised 3571 m above sea level, the highest for the year. It was lifted by two kites while other kites supported the wire at distances of 2 km and 3.5 km from the top of the line. A total of 6.3 km of wire was out when the kite reached its highest level; pull ranged from 45 to 68 kg. Maximum altitudes continued to increase. The maximum altitude by a single kite of 3800 m, a record that still stands, was reached in 1896.

The peak in activity was in 1900. During that year, the mean height of 2576 m was achieved. The highest was 4815 m. By this time the kites could be reeled in and out rapidly, sometimes at rates exceeding the equivalent of 100 m min-1 of vertical height. The kite flying experimentation at Blue Hill was terminated in 1904.

It was felt that the instrumental development and flying technology were "perfected" by that time. However, soundings by means of kites continued for many years, mostly on designated "international days". With the start of hostilities in World War I, all international cooperation ended. With that the exchange of sounding data and the kite sounding program at Blue Hill ended quietly.

The scientific benefit from the Blue Hill Program was immense. Bjerknes, the Norwegian meteorologist who developed the frontal theory that is still the basis of modern day weather forecasting, credited kite soundings from Blue Hill as providing the necessary observational data for his cyclone development theory to be advanced and tested.

Bjerknes proposed that baroclinicity (strong horizontal temperature gradients in the atmosphere) was the basic source of energy conversion in cyclone development. Kite sounding data showed baroclinic zones to be present ahead and behind the storm centre corresponding to what were later known as frontal zones.

Clayton, an American meteorologist, in 1899 related kite sounding data to their position relative to cyclones and anticyclones. From this, two important aspects of atmospheric structure were revealed. Firstly, Clayton concluded that axis of the cyclone, more generally known as a low pressure system, slopes westward with height. He then concluded that cyclones and anticyclones are but secondary phenomena in great waves (later to become known as Rossby waves) of alternately warm and cold air that sweep across the United States.

From kite ascensions of long duration came the discoveries of the planetary boundary layer. It was learned that diurnal change of temperature, found at all heights on mountain stations, disappeared at a height of about 1 km in the free air and that the temperature is generally lower and the wind speed higher on mountains than in the free air.

The U.S. Weather Bureau opened sixteen observation stations in 1898, which simultaneously sent up instrument-carrying kites. By 1919, however, progress made with sounding balloons led the Weather Bureau to curtail daily kite ascensions and continue such flights only on special occasions. Eventually, the inauguration of airplane observations superseded kite stations in 1931 and the last kite station, Ellendale, North Dakota, was closed in July 1933.

Outside of the U.S. the most active kite flying program was the German Weather Bureau. The record for the highest flying train of kites on a single line was set between Lindenberg and Herzberg in Germany on August 1, 1919. This flight, which involved a series of eight kites, reached a maximum altitude of 9740 m. The kite line broke during retrieval when the line tension was 145 kg.

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