Radiosonde balloons

B. Geerts and E. Linacre

7/'98


(photo source: US National Weather Service)

Radiosondes are carried aloft by balloons to measure and simultaneously transmit recorded data, which includes pressure, temperatures and humidity. Winds are determined by using an instrument that tracks the radio signal transmitted from the radiosonde, or an inertial navigation system that transmits accelerations, or a GPS (Global Position Satellite) receiver that transmits the sonde's locations

Data from the radiosonde is interpreted at the launching station and entered into a worldwide communications network. In this manner, information is relayed to weather forecast centers around the globe. Radiosonde observations usually are taken twice daily at 0000 hours (midnight) and 1200 hours (noon) Greenwich mean time. One to two thousand such observations are taken across the globe.

Balloons generally reach altitudes as high as 30 km prior to bursting, about 90 minutes after launch. Horizontal distances traveled by the balloon may exceed 200 km, but this varies significantly due to the nature of winds in the upper atmosphere. Radiosonde balloons are inflated with either helium or hydrogen gases and are usually launched in an open field, generally at an airport where obstructions are at a minimum. When completely inflated, the balloon is about 2 m in diameter at the launch site. Just before bursting, its diameter has increased to 12-15 m. The balloon as well as the instrument suspended from it can be ingested by a jet engine without causing significant engine damage.

The first routine measurements of temperature and wind profiles were made by August Angot from 1890 to '95, on the then new Eiffel tower in Paris, however these profiles only reached up to 302m. Routine radiosonde observations started in several countries in the 1930's, but the balloons in those days ascended only to 10-18 km. A British weather balloon was reported in 1947 (1) as having ascended to 30 km. The balloon material has to be lightweight, able to withstand considerable stretching as the contained gas expands 50 times or so, and still be flexible at temperatures as low as -80C.

 Current and old radiosonde data from around the world can be found, both in text and graph formats, at the University of Wyoming website.

Reference

(1) Bulletin of the American Meteorological Society 1997,78, p.2879