Weather balloon

A weather balloon also known as sounding balloon is a balloon (specifically a type of high-altitude balloon) that carries instruments aloft to send back information on atmospheric pressure, temperature, humidity and wind speed by means of a small, expendable measuring device called a radiosonde. To obtain wind data, they can be tracked by radar, radio direction finding, or navigation systems (such as the satellite-based Global Positioning System, GPS). Balloons meant to stay at a constant altitude for long periods of time are known as transosondes. Weather balloons that do not carry an instrument pack are used to determine upper-level winds and the height of cloud layers. For such balloons, a theodolite or total station is used to track the balloon's azimuth and elevation, which are then converted to estimated wind speed and direction and/or cloud height, as applicable.

Transosonde ready for release
Picture taken at approximately 30 km above Oregon using a 1,500 gram weather balloon
Rawinsonde weather balloon just after launch. Notice a parachute in the center of the string and a small instrument box at the end. After release it measures many parameters. These include temperature, relative humidity, pressure, and wind speed and wind direction. This information is transmitted back to surface observers.

History

One of the first persons to use weather balloons was Léon Teisserenc de Bort, the French meteorologist. Starting in 1896 he launched hundreds of weather balloons from his observatory in Trappes, France. These experiments led to his discovery of the tropopause and stratosphere.[1] Transosondes, weather balloons with instrumentation meant to stay at a constant altitude for long periods of time to help diagnose radioactive debris from atomic fallout, were experimented with in 1958.[2]

Materials and equipment

The balloon itself produces the lift, and is usually made of a highly flexible latex material, though Chloroprene may also be used. The unit that performs the actual measurements and radio transmissions hangs at the lower end of the string, and is called a radiosonde. Specialized radiosondes are used for measuring particular parameters, such as determining the ozone concentration.

The balloon is usually filled with hydrogen due to lower cost, though helium can also be used. The ascent rate can be controlled by the amount of gas with which the balloon is filled. Weather balloons may reach altitudes of 40 km (25 mi) or more, limited by diminishing pressures causing the balloon to expand to such a degree (typically by a 100:1 factor) that it disintegrates. In this instance the instrument package is usually lost.[3] Although a parachute may be used to help in allowing retrieval of the instrument. Above that altitude sounding rockets are used, and for even higher altitudes satellites are used.

Launch time, location, and uses
A hydrogen filled balloon at Cambridge Bay Upper Air station, Nunavut, Canada

Weather balloons are launched around the world for observations used to diagnose current conditions as well as by human forecasters and computer models for weather forecasting. About 800[4] locations around the globe do routine releases, twice daily, usually at 0000 UTC and 1200 UTC. Some facilities will also do occasional supplementary "special" releases when meteorologists determine there is a need for additional data between the 12-hour routine launches in which time much can change in the atmosphere. Military and civilian government meteorological agencies such as the National Weather Service in the US typically launch balloons, and by international agreements almost all the data are shared with all nations.

Specialized uses also exist, such as for aviation interests, pollution monitoring, photography or videography and research. Examples include pilot balloons (Pibal). Field research programs often use mobile launchers from land vehicles as well as ships and aircraft (usually dropsondes in this case). In recent years weather balloons have also been used for scattering human ashes at high-altitude. The weather balloon was also used to create the fictional entity 'Rover' during production of the 1960s TV series The Prisoner in Portmeirion, Gwynedd, North Wales, UK in September 1966. This was retained in further scenes shot at MGM Borehamwood UK during 1966–67.[5]

See also

References
  1. Chisholm, Hugh, ed. (1922). "Teisserenc de Bort, Léon Philippe" . Encyclopædia Britannica (12th ed.). London & New York: The Encyclopædia Britannica Company.
  2. Staff (February 1958). "Chief Special Projects Section: Dr. Lester Machta" (PDF). United States Weather Bureau: 39–41. Retrieved 21 April 2012. Cite journal requires |journal= (help)
  3. Radiosonde
  4. NWS factsheet Archived 2016-02-20 at the Wayback Machine
  5. Paul-Davies, Steven (2002). The Prisoner Handbook. London: Pan Books. ISBN 978-0-230-53028-7.
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