Balloons and Meteorology
Preparing to launch America''s first "ballon-sonde." Since this first
launch on September 15, 1904, in St. Louis, Missouri, literally millions
of weather balloons have been launched by the National Weather Service and
its predecessor organization.
Balloons are ideal for
gathering meteorological information and have been used for that purpose
throughout their history. Meteorological measurements of wind and air
pressure have gone hand in hand with the earliest balloon launches and
continue today. Balloons can climb through the denser air close to the
Earth to the thinner air in the upper atmosphere and collect data about
wind, the different layers of the atmosphere, and weather conditions as
The first meteorological
balloon sondes, or "registering balloons," were flown in France in 1892.
These balloons were relatively large, several thousand cubic feet, and
carried instruments to record barometric pressure (barometers),
temperature (thermometers), and humidity (hygrometers) data from the upper
atmosphere. They were open at the base of the balloon and were
inflated with a lifting
gas, which could be hydrogen, helium, ammonia, or methane.
The lifting gas in the balloon exited through the opening as the balloon
expanded during its ascent and the air became thinner and the pressure
dropped. At the end of the day, as the lifting gas cooled and took up less
space, the balloon descended very slowly. The meteorologists had to wait
until the balloon descended all the way to Earth to retrieve their
instruments, which often had drifted up to 700 miles (1,126 kilometres)
from their launch point.
The German meteorologist
Assmann solved the problem of drifting balloons and retrieval of
instruments in 1892 by introducing closed rubber balloons that burst when
they reached a high altitude, dropping the instruments to Earth by
parachute much closer to the launch site. These balloons also had fairly
constant rates of ascent and descent for more accurate temperature
readings. Assmann also invented a psychrometer, a type of hygrometer used
to measure humidity in the air that laboratories generally use.
In the 1930s,
meteorologists were able to get continuous atmospheric data from balloons
when the radiosonde was developed. A radiosonde is a small, radio
transmitter that broadcasts or radios measurements from a group of
instruments. Balloons, usually unmanned, carry the transmitter and
instruments into the upper atmosphere. The radiosonde transmits data to
Earth while measuring humidity, temperature, and pressure conditions.
Two men performing balloon tests for the U.S.
Today, three types of
balloons are commonly used for meteorological research.
Assmann's rubber, or neoprene, balloon is used for measuring vertical
columns in the atmosphere, called vertical soundings. The balloon,
inflated with a gas that causes the balloon to rise, stretches as it
climbs into thin air, usually to around 90,000 feet (27,400 meters). Data
is taken as the balloon rises. When the balloon has expanded from three to
six times its original length (its volume will have increased 30 to 200
times its original amount), it bursts. The instruments float to Earth
under a small parachute. The neoprene balloon can either carry radiosondes
that transmit meteorological information or be tracked as a pilot balloon,
a small balloon sent aloft to show wind speed and direction. Around the
world, balloons equipped with radiosondes make thousands of soundings of
the winds, temperature, pressure, and humidity in the upper atmosphere
each day. But these balloons are launched and tracked from land, which
limits what the radiosondes can measure to less than one-third of the
(usually polyethylene) balloons were first launched in 1958. They carry
scientific instruments to a predetermined atmospheric density level.
Zero-pressure balloons are the best for extremely high altitudes because
the balloons can be lighter and stress on them can be distributed over the
surface of the balloon.
A zero-pressure balloon being inflated at Alice
About the same time, the
Air Force Cambridge Research Laboratories (AFCRL) started working on
super-pressure balloons, which were made from Mylar.
The development of Mylar plastic films and advances in
electronic miniaturization made constant-altitude balloons possible.
Mylar is a
plastic that can withstand great internal pressure. The Mylar
super-pressure balloon does not expand as it rises, and it is sealed to
prevent the release of gas as the balloon rises. By the time the balloon
reaches the altitude where its density equals that of the atmosphere, the
gas has become pressurized because the heat of the sun increases the
internal gas pressure. However, because Mylar can withstand great internal
pressure, the volume of the balloon remains the same.
By carefully calculating the weight of the
balloon and whatever it is carrying, the altitude at which the balloon
will achieve equilibrium and float can be calculated. As long as the
pressure inside the balloon remains the same, it will remain at that
These balloons could be
launched to remain aloft at specified altitudes for weeks or months at a
time. Moreover, satellites could be used to track and request data from
many balloons in the atmosphere to obtain a simultaneous picture of
atmospheric conditions all over the globe. Another advantage of
super-pressure balloons is that, since they transmit their data to
satellites, they can gather data from over oceans as well as land, which
is a limitation of balloons equipped with radiosondes.
The AFCRL program resulted
in the Global Horizontal Sounding Technique (GHOST) balloon system. With
GHOST, meteorologists at last achieved their goal of semi-permanent
platforms floating high in the atmosphere.
balloons were launched starting in March of 1966. The GHOST balloons and
their French counterpart, EOLE, (the name Clement Ader used for one of his
aircraft—named after the Greek god of the wind) used strong, plastic
super-pressure balloons to trace air circulation patterns by drifting with
the wind at constant density altitudes. Many super-pressure balloons were
aloft at a time, grouped at constant density levels. Each balloon had a
sensing device and transmitting system for gathering information on its
position and weather data and transmitted atmospheric and weather data to
weather satellites. They first transmitted their data to the NASA
satellite in 1970.
In 1966, a GHOST balloon
circled the Earth in 10 days at 42,000 feet (12,801 meters). By 1973, NASA
had orbited scientific instrument packages aboard sealed balloons at
altitudes up to 78,000 feet (23,774 meters). Other GHOST balloons remained
aloft for up to a year. The program lasted for 10 years.
The ultimate of the
super-pressure balloons was the balloon satellite
Echo I. Launched into space in
1960, the balloon inflated to a sealed volume by residual air, benzoic
acid, and a chemical called anthraquinone.
Constant-altitude, super-pressure balloons continue to fly over the oceans
and land surfaces. These balloons have
been relied on for decades to provide extensive knowledge of global
meteorology and improve worldwide weather forecasting.