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A direct descendant of the historical meteograph, a radiosonde is an atmospheric measurement device that transmits readings and data via radio waves to a receiver. Radiosondes are capable of measuring a variety of atmospheric conditions, including temperature, humidity, wind speed and direction, and more. The devices are utilized in weather balloons to monitor these conditions and have been in common use since 1930.
There are different types of radiosondes in existence, each with differing measurement characteristics. An ozonesonde is designed specifically to measure levels of ozone concentration in the atmosphere, while rawinsondes are only intended to measure wind direction and speed as opposed to the full range of measurements provided by a radiosonde. The majority of radiosondes are launched from one of more than 800 authorized launch sites across the world via hydrogen or helium-filled balloons.
Some radiosondes are dropped from aircraft, most commonly when the intention is to record conditions in a specific location, such as in the center of a storm cloud. These devices are known as dropsondes. Radiosondes have been regularly used to monitor weather activity and to predict future weather events. Their use in weather balloons, and through the launching of dropsondes, has provided invaluable data for weather predictions and research into storm activity.
Developed initially in 1929 by Robert Bureau in France, the name is derived from two features of the device — radio, due to the way in which the information is transmitted from the device and sonde, being a French word meaning probe. Bureau’s design was not adopted as a standard, however, although his naming of the device remained. A year later, a radiosonde that transmitted its information in Morse code was developed and launched by Pavel Molchanov. By utilizing the internationally recognized on-off textual code, readings from the Molchanov radiosonde could be easily read and understood without the requirement of specialist equipment or individual training. The Molchanov device was used as the standard from which all future radiosonde designs were created.
A key indicator in weather predictions, the upper air readings provided by radiosondes are utilized in the interpretation of thermodynamics, humidity, and temperature. The readings from these upper air locations can indicate incoming weather conditions. Similar measures can be taken in lower atmospheres to provide guidance in regard to potential tornado conditions. These tornado prediction tests are regularly undertaken in and around Oklahoma City, Oklahoma, in the United States during the tornado seasons of March and April each year.