Behind the Forecast: Weather Balloons

Behind the Forecast: Weather Balloons
Weather balloons are a vital part of how meteorologists get information about our atmosphere. (Source: Tawana Andrew)

Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.

LOUISVILLE, KY (WAVE) - Weather balloons are a vital part of how meteorologists get information about our atmosphere. They are launched by every single day, twice a day from almost 900 locations around the world. These balloons can drift more than 100 miles away, rising around 20 miles up into the atmosphere, flying for around two hours.

Maps showing station locations of NWS offices that take radiosonde observations
Maps showing station locations of NWS offices that take radiosonde observations (Source: National Weather Service)

While rudimentary upper air observations were being conducted as early as 1749 (first by thermometers attached to kites), the first GPS based system was not installed by the National Weather Service until 2005.

The balloons themselves are made of synthetic rubber or latex and filled with hydrogen or helium. They initially are around six feet wide when they are inflated and expand to nearly 20 feet across as they rise up.

Attached to the balloon is a radiosonde and a parachute for the radiosonde. Here’s how the National Weather Service describes them:

“An instrument.....attached to the balloon to measure pressure, temperature and relative humidity as it ascends up into the atmosphere. These instruments will often endure temperatures as cold as -139°F (-95°C), relative humidities from 0% to 100%, air pressures only a few thousandths of what is found on the Earth’s surface, ice, rain, thunderstorms, and wind speeds of almost 200 mph! A transmitter on the radiosonde sends the data back to tracking equipment on the ground every one to two seconds. By tracking the position of the radiosonde, we can also calculate wind speed and wind direction. The radiosonde is powered by a small battery.”

As the balloon rises it expands until it bursts; there’s less air in the upper atmosphere so there’s less pushing back on the balloon, and since the pressure is lower, the balloon expands. The parachute slows the radiosonde as it falls back to earth after the balloon bursts. The radiosonde falls slowly to the ground at speeds less than 22 mph after the balloon bursts.

Radiosondes are lifted into the atmosphere by large weather balloons.
Radiosondes are lifted into the atmosphere by large weather balloons. (Source: National Weather Service)

The information gathered by weather balloon is used by computer models to figure out the forecasts. The information is also quite invaluable for severe storm, marine and aviation forecasts. It’s used in weather research, inputted in air pollution models and provides verification (ground truth) for satellite data.

The information received from the radiosonde (temperature, humidity, winds) is plotted on what’s called a Skew-T chart. These are used to figure out where clouds are, severe weather potential, snow potential and much more.

Attached to the handle of the radiosonde is a postage-paid mailing bag. If you find one of them, you can put it in the bag and mail it back to the NWS, for recycling into future radiosondes. If you find a fallen NWS radiosonde, follow the instructions on this website.

Science Behind the Forecast: Weather Balloons

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