Twice a day, every day of the year, weather technicians release about six-foot round weather balloons from 900 locations worldwide. Weather balloons are made of latex or synthetic rubber (neoprene) and filled with hydrogen or helium—gases that are lighter than air. The neoprene envelope is about 0.051mm thick. An instrument called a radiosonde is attached to the balloon to measure pressure, temperature, and relative humidity as it climbs up into the atmosphere. The radiosonde is powered by a small battery.
After an hour of flight, the balloon reaches 100,000 feet (about 20 miles or 30 kilometers). This is the stratosphere— the second-last layer of the atmosphere before outer space. This layer holds 19% of the atmosphere’s gases but very little water vapor. In this region, the temperature increases with height. From the stratosphere, the infinite vastness of the universe is a breathtakingly beautiful panorama. Only few astronauts and aeronauts on scientific balloon missions have been able to observe this. The Earth appears as a curved brown and bluish-green expanse against a black outer space, and the sky transitions from a deep blue to absolute black.
As the balloon rises, it expands up to 20 feet in diameter. Its rubber envelope stretches to its limit and thins out to 0.0025 mm. Now, the balloon has reached a bursting altitude. When the balloon bursts, the radiosonde is sent plunging toward Earth, but it is quickly slowed to 22 miles per hour by a parachute which opens within seconds. Because of its slow descent, most of the time, the radiosonde lands safely and can also be reused.
Generally, the balloon flight lasts for two hours and can drift as far as 125 miles. During the ascent, the balloon and the instruments endure temperatures as cold as -139°F (-95°C), wind speeds of 200 mph, relative humidity from 0% to 100%, ice, rain, thunderstorms, and extremely low air pressure— only a few thousandths of what is found on the Earth’s surface!
Throughout its near-space journey, a transmitter on the radiosonde beams atmospheric information back to tracking equipment on the ground every one to two seconds. By tracking the position of the radiosonde, meteorologists can also calculate wind speed and wind direction.
To collect weather data at night, a lightstick is attached to the balloon, which enables meteorologists to track the balloon until the tracking equipment locks onto the radio signal.
Nowadays, weather balloons are the primary source of data to plot out weather conditions for days in advance. A century ago, forecasters could not predict the weather beyond a few hours as their only source of information was weather measurements taken on the ground. High-altitude weather conditions can be different from those at sea level. So when a squadron of weather balloons picks this data from the upper atmosphere they alert us many days in advance about thunderstorms, tornadoes, snow blizzards, flash floods, and a lot of other critical information that helps save lives and prepare for a weather emergency.
Computer forecast models which use weather balloon data are used by all forecasters worldwide, from National Weather Service meteorologists to your local TV weatherman!
Notable Contributions to the Science of Meteorology
The science of meteorology was born with the invention of the mercury barometer and dates back to the mid-17th century. The great Italian scientist Evangelista Torricelli introduced and demonstrated the mercury barometer to the public. He explained that the fluctuations in the mercury column of a barometer corresponded to the changes in atmospheric pressure. In honor of Torricelli, the torr came to be known as a unit of pressure equal to one millimeter of mercury. Toricelli who died at the age of 39, in 1647, was also the first to claim that we live at the bottom of the ocean of air, where atmospheric density is at its maximum; as we climb higher, the air becomes thinner resulting in low atmospheric density. Therefore, with increasing altitude, oxygen levels in our blood decrease with the decrease in oxygen.
Specifically, the credit for early weather observations, from a balloon, goes to Dr. John Jeffries. His first balloon flight was a frightening and disappointing experience, but also historic and triumphant in a different way! Born in 1744, Dr. Jeffries, a Harvard-educated physician also had a great deal of interest in learning about the atmosphere. While practicing in England, he paid an astronomical 700 pounds to French balloonist Jean-Pierre Blanchard to build a balloon for the crossing of the English Channel. Jeffries’ condition was that he should be allowed on the journey with his scientific instruments to take some weather measurements.
On 7th January 1785, the duo took off on a daunting balloon crossing of the English Channel. They launched from the English side to fly across to France, but the
balloon threatened to crash in the English Channel. To make the balloon lighter and to keep it afloat, Jeffries was compelled to throw away his instruments. Still the balloon refused to ascend, and the aeronauts were forced to dump everything, including their clothes. Eventually, their balloon caught a rising warm air current, which landed them in Calais in France, as naked as the trees, writes Jeffries; thankful to be alive and for achieving the triumphant crossing of the dangerous English Channel.
Jeffries is credited with being among America’s first weather observers and his birthday 5th February is celebrated as National Weatherperson’s Day in his honor.
As a matter of fact, brilliant research by some chemists and physicists of the 17th and 18th centuries yielded significant scientific breakthroughs that contributed to the understanding of many unknown aspects of the atmosphere.
Only few examples are mentioned here. Robert Boyle and Jacques-Alexandre-César Charles formulated the laws of gas pressure, temperature, and density; Isaac Newton and Gottfried Wilhelm Leibniz’s developed calculus; Joseph Black came up with the doctrine of latent heat (i.e., heat release by condensation or freezing) and John Dalton developed the law of partial pressures of mixed gases. These important insights led to more progress in science and technology and eventually to the development of the modern weather balloon and instruments that help to produce useful weather forecasts.
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(8 October 2012) weather.gov <http://www.srh.noaa.gov/bmx/?n=kidscorner_weatherballoons>
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6. Lennart Ege, Balloons and Airships (New York: MacMillan Publishing, 1974), 103-105
7. Fulgence Marion: Wonderful Balloon Ascents (1870)