Weather balloons are launched
from the upper air building which is located in a valley adjacent to
the forecast office (pictured, top row left). They are filled with helium
inside of the small building (pictured, top row center and right), then
taken outside to launch (pictured, bottom row center). The helium, which
is a very light gas, allows the balloon to reach heights of 60,000 feet
above the earth's surface in about an hour. As the balloon rises, the
atmosphere thins and the pressure outside the balloon decreases allowing
the balloon to expand and eventually break. This usually happens within
two hours of the launch at elevations of 80,000 to 120,000 feet.
An instrument, called a radiosonde,
is tethered to the balloon (pictured, bottom row center). As the balloon
rises through the air, the radiosonde measures temperature, relative
humidity, and pressure. A transmitter within the radiosonde transmits
this data back to a receiver located in the shelter (pictured, bottom
row right). The receiver tracks the azimuth and range of the balloon
as it ascends. From this information, the wind speed at various levels
in the atmosphere can be calculated.
After the balloon flight is
complete, a technician ensures the data is accurate before it is disseminated.
Additional quality control checks are done at one of our national centers
before the data is incorporated into computer models which meteorologists
use to make their forecasts.
The balloons are launched
from hundreds of locations around the world twice a day every day of
the year. The launches occur simultaneously worldwide! This gives
meteorologists a snapshot of the earth's three-dimensional atmospheric
But what happens to the
radiosonde when the balloon breaks? The radiosonde is protected
by a styrofoam container, which cushions the radiosonde upon impact
with the ground. However, a small parachute will also pop out as the
radiosonde falls, slowing its descent.
Are the radiosondes returned?
Frequently, the radiosondes are discovered in a pasture, grove of
trees, creek, peoples' backyards and other locations. A self-addressed
postage-paid envelope, which is in a compartment of the radiosonde container,
can be used to return the radiosonde to a reconditioning center for
repair, and eventual reuse. Most of the radiosondes launched from this
office follow the prevailing wind and wind up dropping into the North
Atlantic Ocean, never to be recovered.