What Is a Weather Balloon?

Today’s runaway balloon raises questions about an obscure area of weather science many people are familiar with but know little about. What exactly do weather balloons do?

Nearly all stations in the United States that operate weather balloons use hydrogen gas to inflate them. The basic idea isn't to send weather balloons directly into storms but to have them probe the winds hundreds of miles around them: winds that steer a hurricane and determine its course. As such, the balloons are designed to fly unmanned at the rapid speeds created by storms.

Currently, researchers get information about those steering currents in several ways. Over land, National Weather Service offices launch weather balloons twice a day. Unlike the hurricane balloons, which will float for days, the weather service balloons send back data for between an hour and a half and two hours before they pop and fall back to land.

Ocean going balloons are somewhat more advanced. Sometimes equipped with a GPS units, they are designed to stay aloft from two to seven or more days, sending back their altitude and position every 15 minutes, before losing their helium and crashing into the ocean.

The National Oceanographic and Aeronautics Administration reports that in December 1996, a balloon measured a wind speed of 230 miles an hour at 30,000 ft. Winds aloft may have been even stronger, but the balloon was pushed so far away that we could not continue making accurate calculations of wind speed.

An instrument (called a radiosonde) attached to the balloon measures the atmospheric pressure, air temperature and relative humidity. Wind speed and direction are calculated by tracking the instrument with a high-gain antenna (similar to a satellite-TV dish).

Some balloons rise at an average of 1,000 feet per minute. They typically bursts around 100,000 ft above ground—where the atmospheric pressure is one percent the pressure at sea-level.