Radiosondes are instruments used by weather agencies around the world to collect weather information. These instruments are carried aloft by hydrogen filled balloons to measure and simultaneously transmit recorded data which include pressure, temperatures and humidity. Winds are determined by using an instrument that tracks the radio signal transmitted from the radiosonde. Vertical data from the radiosonde is interpreted at the launching station and entered into a worldwide communications network. In this manner, information is relayed to various forecast centers around the globe.
Radiosonde observations are taken twice daily at 0000 hours and 1200 hours Greenwich Mean Time (GMT), or at 6 pm and 6 am CST. All worldwide agencies launch their radiosondes at approximately the same time, and over 1500 such observations are taken daily.
In the United States, data is collected at the National Center for Environmental Prediction (NCEP) in Washington, D.C. The radiosonde data is processed together with over 25,000 surface observations, hundreds of aircraft reports and a wealth of satellite data. Location, movement, as well as strength of the weather systems that circle the earth are analyzed from this data. Through mathematical equations, large supercomputers at NCEP then project weather patterns anywhere from 3 to 7 days into the future. The NCEP computers produce a wide assortment of maps and numerical forecast data, and these are then relayed to field forecast offices (such as NWS Mobile) where local and regional weather forecasts are prepared.
Here close to home along the Central Gulf Coast, the New Orleans, Jackson, Birmingham, and Tallahassee NWS Offices are stations in the worldwide network which launch radiosondes twice daily. Although not identical, the balloon and instrument package released by our offices are similar to those used by other nations, including Mexico and Canada.
Balloons generally reach altitudes as high as 100,000 feet prior to bursting about 90 minutes after launch. Distances traveled by the balloon may vary significantly due to the nature of winds in the upper atmosphere. The atmosphere that encircles the earth flows as vast rivers, and winds often show tremendous variations in direction and speed as a balloon rises. During a balloon ascent, winds may completely reverse direction or range from calm at the surface to over 200 mph in high level jet streams.
Data on winds, temperatures and humidity help forecasters predict clouds, rain and the paths of major storms. The information is also critical to the prediction of a variety of severe weather events which includes defining the threat of tornadoes, damaging thunderstorms or high winds.
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 reaches about 8 to 10 feet in height.
Information relating to the data and location of launch are stamped on the package prior to release. A manufacturers number is also carried on the package. A parachute is attached to the radiosonde just prior to launch. This prevents destruction of the instrument so that it can be reused.
As you might imagine, the radiosonde weather balloon plays a significant part in the observation, analysis and prediction of the world's weather. In spite of advances in satellite and computer technology, the weather balloon remains a very significant and integral part of the worlds weather observation network.
For more information on the NWS radiosonde network, visit NOAA's upper air page.