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Radiosonde
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Radiosondes
are instruments used by weather agencies around the world to collect
weather information. These instruments are carried aloft by hydrogen
filled balloons to measure and simultaneously transmit recorded data
which include pressure, temperatures and humidity. Winds are determined
by using an instrument that tracks the radio signal transmitted from
the radiosonde. Vertical
data from the radiosonde is interpreted at the launching station
and entered into a worldwide communications network. In this manner,
information is relayed to various forecast centers around the globe.
Radiosonde observations are taken twice daily at 0000 hours and 1200
hours Greenwich Mean Time (GMT), or at 6 pm and 6 am CST. All worldwide
agencies launch their radiosondes at approximately the same time,
and over 1500 such observations are taken daily.
In the United States, data is collected at the National Center for
Environmental Prediction (NCEP) in Washington, D.C. The radiosonde
data is processed together with over 25,000 surface observations,
hundreds of aircraft reports and a wealth of satellite data. Location,
movement, as well as strength of the weather systems that circle the
earth are analyzed from this data. Through mathematical equations,
large supercomputers at NCEP then project weather patterns anywhere
from 3 to 7 days into the future. The NCEP computers produce a wide
assortment of maps and numerical forecast data, and these are then
relayed to field forecast offices (such as NWS Mobile) where local
and regional weather forecasts are prepared.
Here close to home along the Central Gulf Coast, the New Orleans,
Jackson, Birmingham, and Tallahassee NWS Offices are stations in the
worldwide network which launch radiosondes twice daily. Although not
identical, the balloon and instrument package released by our offices
are similar to those used by other nations, including Mexico and Canada.
Balloons generally reach altitudes as high as 100,000 feet prior to
bursting about 90 minutes after launch. Distances traveled by the
balloon may vary significantly due to the nature of winds in the upper
atmosphere. The atmosphere that encircles the earth flows as vast
rivers, and winds often show tremendous variations in direction and
speed as a balloon rises. During a balloon ascent, winds may completely
reverse direction or range from calm at the surface to over 200 mph
in high level jet streams.
Data on winds, temperatures and humidity help forecasters predict
clouds, rain and the paths of major storms. The information is also
critical to the prediction of a variety of severe weather events which
includes defining the threat of tornadoes, damaging thunderstorms
or high winds.
Radiosonde balloons are inflated with either helium or hydrogen gases
and are usually launched in an open field, generally at an airport
where obstructions are at a minimum. When completely inflated, the
balloon reaches about 8 to 10 feet in height.
Information relating to the data and location of launch are stamped
on the package prior to release. A manufacturers number is also carried
on the package. A parachute is attached to the radiosonde just prior
to launch. This prevents destruction of the instrument so that it
can be reused.
As you might imagine, the radiosonde weather balloon plays a significant
part in the observation, analysis and prediction of the world's weather.
In spite of advances in satellite and computer technology, the weather
balloon remains a very significant and integral part of the worlds
weather observation network.
For more information on the NWS radiosonde network, visit NOAA's
upper air page.
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