On this date in 1929, the first radiosonde was sent up by French meteorologists. A radiosonde is a balloon that is released from a ground station. It rises to a height of about 80,000 feet, transmitting atmospheric conditions by radio back to the ground station.
Upper air stations all over the world release a balloon at midnight and noon Greenwich Mean Time. This gives meteorologists a comprehensive snapshot of upper air conditions around the globe.
The balloon measures about five feet in diameter and is filled with hydrogen. A cable that is about one hundred feet long trails below the balloon. The cable is so long because air movement around the balloon cannot affect the readings. At the end of this cable is an instrument package that contains a thermometer, hygrometer and barometer.
As the balloon ascends, it gradually expands and bursts at a height of about 80,000 feet. The package has a parachute to help it float back to ground where instructions direct the finder to return it to the Weather Service.
