Dane+Sackett+weather+balloons

Weather balloons are launched every 12 hours all over the world. There are 70 sites around the United States and more than 700 more sites in the world. The are all launched at the same time using the Greenwich Mean Time system. Weather balloons have been used since World War II and they provide data on temperature, pressure, relative humidity, and wind velocity. All of this data is then sent to a central computer in Maryland. The rubber weather balloons are filled to about 2 m with either helium or hydrogen and then have an instrument package attached to each balloon by a 15-m cord. The balloon rises and once it reaches a height of 30 km the volume is so great the balloon bursts. The instrument package is then safely parachuted to the ground. This intstrument package records all the data from the balloon.