Meterological balloons

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Meterological Ballons

  • Weather balloons  are typically teardrop shaped rubber enclosure about two meters in diameter filled with sufficient helium to loft an instrument package to very high atmospheric levels.
  • Data on the pressure, temperature and humidity are collected during its ascent.Winds are calculated from the measured position of the balloon during its ascent.
  • The balloon grows larger as it reaches lower and lower atmospheric  pressures until it finally bursts after expanding to six meters or more in diameter.

  • The Instrument package for  weather balloons has evloved over time into a smaller unit with better sensors,now typically with a mass of only a few hundred grams depending on the model  and features.This package was originally called a radio Meteorograph  but is now referred to as a radiosonde.
  • Radio for the battery powered transmitter that sends atmospheric data back to earth as the ballon ascends and sonde for the meterological sounding produced from the transmitted data.



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    • A modern Radiosonde is monitored by its radio signals using various types of radio direction finding equipment. The ascent rate of a weather balloon is approximately constant and is known, So the pressure reading can be related to geometric altitudes. 
    • Data transmitted by the radiosonde are recorded by ground equipment and then transmitted around the world so that all nation contribute to an international pool of radiosonde data and  also obtain radiosonde measurements from other countries.
    • Data from a radiosonde ( temperature, humidity  and wind various pressure levels) can be plotted on a  thermodynamic diagram as an atmospheric  sounding  or on a chart to create a weather map at a given upper level. In addition, radiosonde data are very important in computer models of NWP( Numerical Weather Prediction). 
    • Early weather balloon instrument packages did not have radio transmitters to allow their tracking. Rather the balloon carried a radar reflector which was actively tracked and located by radar, or by a radio  theodolite. 
    • This kind of weather balloon and instrument packages was called a rawinsonde for radar plus wind plus sondes.Upper winds were calculated from the various position of the balloon recorded by the tracking procedure. A radio transmitter sends back temperature and humidity data.


    Balloon Launchings

    A balloon ascent can last more than two hours and the balloon can drift as much as 200 Km. For this reason , the balloon are generally launched about 45 minutes before the time at which  their data are considered valid to allow them to raise into the stronger winds of upper levels in the atmosphere.

     In ideal conditions , weather balloons are capable of reaching altitudes of 30Km at pressures typically about 1/100 th of that at the earth surface, although not all of them  make it that high. The temperature sensor is designed to record temperatures as low as minus 90 degree Centigrade.





      

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