Autumn-Weather+Balloons

weather balloons page 387
Weather Balloons are used to provide the data for the country's weather forecasts. These devices have been used since World War II to provide temperature, pressure, relative humidity, and wind velocity profiles in the upper atmosphere. there are 70 launching sites in the U.S. and more than 700 in the world. Balloons are released at the same time in all countries at 6:00 and 18:00 hours GMT. Data from allover the world reach the U.S. via a central computer in Maryland. From there, the data is then sent to regional weather service stations throughout the country to be put into newspapers and television and radio networks. The rubber balloons are inflated with either helium or hydrogen to a diameter of about 2m. They becaome buoyant because the density of either gas is less than the density of air. An instrument package is attached to each balloon by a 15-m cord. As the pressure in the atmosphere decreases, the gas inside the balloon expands, making the balloon go higher. When it reaches 30km, the volume of the gas is so great the balloon bursts. a parachute carries the package containing the radio transmitter and measuring instruments safely to the ground.