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How does a weather balloon work?

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Quick answer

A weather balloon carries a small instrument package into the upper atmosphere. Filled with helium or hydrogen, it rises because the gas is lighter than air. As it climbs, falling pressure lets the gas expand until the balloon bursts, and the instruments return by parachute.

A weather balloon works by carrying instruments into the upper atmosphere to measure temperature, pressure, humidity and wind. The balloon rises because helium or hydrogen inside is less dense than air, and it bursts when the gas expands too much.

Step by step

  1. The balloon is filled with a measured amount of helium or hydrogen, giving it lift.
  2. A radiosonde, a small box of sensors, is attached below the balloon.
  3. The balloon is released and rises through the atmosphere at a few metres per second.
  4. The radiosonde measures temperature, pressure, humidity and position, sending data by radio.
  5. Ground equipment tracks the balloon's movement to calculate wind speed and direction.
  6. At high altitude the balloon bursts, and the radiosonde descends by parachute.

Key things to understand

  1. The balloon is filled with a lighter-than-air gas, usually helium or hydrogen, which creates an upward buoyant force.
  2. As the balloon rises, the surrounding air pressure drops, so the gas inside expands and the balloon grows larger.
  3. A small instrument package called a radiosonde hangs below, measuring temperature, pressure, humidity and GPS position.
  4. The radiosonde transmits these measurements by radio to a ground station, which tracks the balloon's path to calculate wind speed and direction.
  5. At a certain altitude the balloon bursts, and the radiosonde falls back to Earth on a small parachute.

Labelled diagram

  1. Launch

    Balloon filled with helium or hydrogen, radiosonde attached, released from ground.

  2. Ascent

    Balloon rises, gas expands as pressure drops, balloon grows larger.

  3. Measurements

    Radiosonde measures temperature, pressure, humidity, and GPS position.

  4. Burst

    Balloon bursts at high altitude when gas expands too much.

  5. Descent

    Radiosonde falls back to Earth on a small parachute.

Weather balloon flight profile

Real-world examples

  • The US National Weather Service launches balloons from about 90 stations across the country twice daily.
  • In India, the India Meteorological Department launches balloons from a network of stations to monitor monsoon winds.
  • During the 2010 Eyjafjallajökull volcano eruption in Iceland, weather balloon data helped track ash movement.
  • Antarctic research stations launch balloons in winter to study the polar vortex and ozone layer.

Common mistake

✗ Myth: Weather balloons are the same as hot air balloons, just smaller.

✓ Fact: Weather balloons use lighter-than-air gases like helium or hydrogen, not heated air. They are uncrewed and designed to burst at high altitude, unlike hot air balloons that carry people and stay aloft.

People also ask

What is a radiosonde?
A radiosonde is a small instrument package carried by a weather balloon. It measures temperature, pressure, humidity, and wind speed and direction as it rises, then transmits the data by radio to a ground station. Radiosondes are used worldwide for weather forecasting and climate research.
Why do weather balloons burst?
Weather balloons burst because the gas inside expands as the surrounding air pressure decreases with altitude. The balloon material stretches until it can stretch no more, then it pops. The burst altitude depends on the balloon's initial size and the amount of gas used.
How do weather balloons help predict weather?
Weather balloons provide vertical profiles of temperature, humidity, pressure, and wind, which are fed into computer forecast models. These data show how the atmosphere is structured and how it is likely to change, improving the accuracy of weather predictions and severe weather warnings.
What happens to the weather balloon after it bursts?
After the balloon bursts, the radiosonde and the remains of the balloon fall back to Earth under a small parachute. Many radiosondes are designed to be returned if found, with instructions and a mailing bag inside, though recovery rates vary.
How high does a weather balloon go?
Most weather balloons reach an altitude of about 20 to 35 kilometres (12 to 22 miles) before bursting. At that height the air is extremely thin, and the balloon has expanded to several times its launch size.
Why do weather balloons carry a parachute?
The parachute slows the fall of the radiosonde so it does not injure people or damage property on landing. It also helps keep the instrument intact, increasing the chance it can be found and reused.
How often are weather balloons launched?
Most weather services launch balloons twice a day, at the same times worldwide, roughly at 00:00 and 12:00 UTC. This synchronised timing gives a consistent snapshot of the atmosphere for weather forecasting.

Part of the guide: Water & Weather Phenomena →