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Close up of a hydrogen filled balloon at Cambridge Bay Upper Air station, Nunavut, Canada

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.

A weather or sounding balloon is a balloon (specifically a type of high altitude balloon) which carries instruments aloft to send back information on atmospheric pressure, temperature, and humidity 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).

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.

In North America prior to release the balloon is usually filled with hydrogen gas due to lower cost, though helium can be used as a substitute. 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 miles) 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. Above that altitude sounding rockets are used. After sounding rockets, satellites are used for even higher altitudes.

Major manufacturers of balloons are Totex and Cosmopren of Japan, Pawan Rubber Products of India, Kaysam (now Kaymont), and Scientific Sales, Inc. of the U.S..

Weather balloons are sometimes cited as the cause for unidentified flying object sightings, e.g. Project Mogul.

Weather balloons are also used for cluster ballooning.

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^[1] 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 is shared with all nations.

Specialized uses also exist, such as for aviation interests, pollution monitoring, 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).

• High altitude balloon
• Radiosonde

1. ^ NWS factsheet

Wikimedia Commons has media related to:

Weather balloon

• Atmospheric Soundings for Canada and the United States - University of Wyoming
• Balloon Lift With Lighter Than Air Gases - University of Hawaii
• Examples of Launches of Instrumented Balloons in Storms - NSSL
• Federal Meteorological Handbook No. 3 - Rawinsonde and Pibal Observations
• Kites and Balloons - NOAA Photo Library
• NASA Balloon Program Office - Wallops Flight Facility, Virginia
• National Science Digital Library: Weather Balloons - Lesson plan for middle school
• Pilot Balloon Observation Theodolites - Martin Brenner, CSULB
• StratoCat - Historical recopilation project on the use of stratospheric balloons in the scientific research, the military field and the aerospace activity
• WMO spreadsheet of all Upper Air stations around the world