Air Meteorology: Weather Balloons

Weather balloons are high altitude flying inflatable bags that use scientific instruments to collect various meteorological data. The purpose of weather balloons is to help people study various aspects of the Earth's weather. Information that they collect includes the temperature, atmospheric pressure, wind speed, and humidity of the atmosphere. Some weather balloons have also been used to measure cosmic radiation, as well as fallout from nuclear weapons tests. Yet, other weather balloon tests include measuring ozone levels and tracking patterns of ozone depletion in the atmosphere. Typical modern balloons work by transmitting weather data back to Earth using a device called a radiosonde. Some balloons are designed to travel for long distances and for many months, while others are meant to expire at sufficiently high altitudes, releasing their radiosonde devices to fall back to Earth via a parachute.

In 1896, a French weather scientist named Leon Teisserenc de Bort built and launched the world's first weather balloons from his laboratory in Trappes, France. He used paper and rubber in the construction of these meteorological devices and filled them with hydrogen to set them afloat. Hydrogen is a type of lifting gas, a gas that weighs less than air. This means a balloon filled with hydrogen will float, much like a bag full of air will float in water. The first weather balloons were very large in order to hold enough gas to remain afloat, and to carry their measuring instruments. These instruments included thermometers to study the air temperature, barometers to measure atmospheric pressure, and hygrometers to record the level of moisture or humidity. Early weather balloons relied on the cooling of their lighter-than-air gases to make them descend, and as a result of varying wind speeds they could drift over 500 miles away from where they were launched. As a result of de Bort's experiments he discovered the edge of the Earth's primary weather-producing atmospheric layer, the troposphere, as well as the next layer, the stratosphere.

At the turn of the century, Adolf Richard Assmann, a German meteorologist, visited de Bort and went on to develop several innovations in weather balloon design. One of these inventions was the psychrometer, which is a more accurate and reliable version of the hygrometer. The sling psychrometer, which is used today, is a direct descendant of this invention. The other was a rubber balloon design that reduced the balloon's drift factor. In addition, the balloon would burst at a certain altitude and release its measuring instruments to fall back to earth using a parachute. Modern balloons still use this design, rising as fast as a thousand feet every minute until they exceed their ability to expand. Afterwards they disintegrate or burst at an altitude of 100,000 feet.

In January of 1929, a French scientist named Robert Bureau developed a device that transmitted precise weather measurements, and called it a radiosonde, which means “radio probe” in French. In 1930, Pavel Molchanov developed a radiosonde that transmitted weather data using Morse code, making it easier to decipher. Modern radiosonde devices will use a small parachute to descend back to Earth when the weather balloon ruptures, decreasing the risk that it will damage property or endanger lives as a result of its landing. They will also use Global Positioning Satellite (GPS) transponders to track the location of the balloon or even help with their retrieval when they fall back to the ground. According to the National Weather Service, as few as one out of five radiosondes that are launched with weather balloons, are recovered when they return to the surface. Those that do get recovered are rebuilt and reused.

Because it is the part that transmits data back home, the radiosonde is the most important part of a weather balloon, aside from its flotation system. The flotation system is a gas-bag that can be made of neoprene, a form of rubber, which is designed to rise quickly, and then burst. Weather balloons meant to reach higher altitudes are typically made using a type of plastic called polyethylene. Other balloons are made of Mylar, a pressure-resistant plastic material, which is used for balloons that are supposed to reach and maintain a set altitude. Mylar balloons stay aloft for long periods of time, and can take readings from directly over the Earth's oceans.

For missions that required staying aloft for months at a time, the Global Horizontal Sounding Technique, or GHOST program, was conceived in 1966. GHOST balloons were specially designed atmospheric probes called “super-pressure” balloons that remained at a constant altitude despite changes in the temperature of the lifting gas inside the balloon. In 1968 a GHOST balloon launched by the National Center for Atmospheric Research reached an altitude of nearly 10 miles and was the first to stay aloft for a full year. The GHOST program lasted for 10 years, during which time 88 balloons were launched. Super-pressure balloons were also used to study the atmosphere of Venus due to their stability. Modern day super-pressure balloons roam the Earth's atmosphere, transmitting data to ground stations and to weather satellites.