Radiosonde

  A radiosonde (Sonde is French for probe) is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. Radiosondes may operate at a radio frequency of 403 MHz or 1680 MHz and both types may be adjusted slightly higher or lower as required. A rawinsonde is a radiosonde that is designed to also measure wind speed and direction. Colloquially, rawinsondes are usually referred to as radiosondes.

The radiosonde was invented and launched for the first time by Soviet meteorologist Pavel Molchanov on January 30 1930.^[1][2] Named "271120", it was released 13:44 Moscow Time in Pavlovsk, USSR from the Main Geophysical Observatory and reached a height of 7.8 kilometers measuring temperature there (-40.7 °C). 32 minutes after the launch radiosonde sent the first aerological message to the Leningrad Weather Bureau and Moscow Central Forecast Institute.^[3]

Modern radiosondes measure or calculate the following variables:

• Pressure
• Altitude
• Geographical position (Latitude/Longitude)
• Temperature
• Relative humidity
• Wind speed and direction

Less commonly, radiosondes may also measure ozone concentration.

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Operation

A rubber or latex balloon filled with either helium or hydrogen lifts the device up through the atmosphere. The maximum altitude to which the balloon ascends is determined by the diameter and thickness of the balloon. Balloon sizes can range from 150 grams to 3000 grams. As the balloon ascends through the atmosphere, the pressure decreases, causing the balloon to expand. Eventually, the balloon will expand to the extent that its skin will break, terminating the ascent. An 800 gram balloon will burst at about 30,000 meters (about 100,000 feet).

The modern radiosonde communicates via radio with a computer that stores all the variables in real-time. The first rawinsondes were observed from the ground with a theodolite, and gave only a wind estimation by the position. Modern radiosondes can use a variety of mechanisms for determining wind speed and direction, such as Loran, radio direction finder, GPS and (in Canada only) Very low frequency. The weight of a radiosonde is typically 250 grams.

Sometimes radiosondes are deployed by being dropped from an aircraft instead of being carried aloft by a balloon. Radiosondes deployed in this way are called dropsondes. They are most often used in special research projects, such as when it is desired to obtain a profile through a specific feature of a storm.

Routine radiosonde launches

Worldwide there are more than 800 radiosonde launch sites. Most countries share data with the rest of the world through international agreements. Nearly all routine radiosonde launches occur at 0000 UTC and 1200 UTC to provide an instantaneous snapshot of the atmosphere. This is especially important for numerical modeling. In the United States the National Weather Service is tasked with providing timely upper-air observations for use in weather forecasting, severe weather watches and warnings, and atmospheric research. The National Weather Service launches radiosondes from 92 stations in North America and the Pacific Islands twice daily. It also supports the operation of 10 radiosonde sites in the Caribbean.

A list of U.S. operated land based launch sites can be found in C, U.S. Land-based Rawinsode Stations of the Meteorological Handbook #3, titled Rawisonde and Pibal Observations, dated May 1997.

California Radiosonde launch sites includes: San Nicolas Island, Edwards AFB, Oakland, Pt. Mugu, San Diego, Vandenberg AFB and Vandenberg AFB South.

Uses of upper air observations

Raw upper air data is routinely ingested by numerical models. Forecasters often view the data in a graphical format, plotted on thermodynamic diagrams such as Skew-T log-P diagrams, Tephigrams, and or Stüve diagrams, all useful for the interpretation of the atmosphere's vertical thermodynamics profile of temperature and moisture as well as kinematics of vertical wind profile.

Radiosonde data is a crucially important component of numerical weather prediction. Because a sonde may drift several hundred kilometers during the 90 to 120 minute flight, there may be concern that this could introduce problems into the model initialization. However, this appears not to be so except perhaps locally in jet stream regions in the stratosphere [1].

In 1985 the Soviet Venus probes Vega 1 and Vega 2 each dropped a radiosonde into the atmosphere of Venus. The sondes could be tracked for two days.

References

1. ^ BALLOONS SAMPLE THE WEATHER. Weather Doctor Almanac (July 2005).
2. ^ Kirk. Martinez,; Jane K. Hart, Edward Linacre, Bart Geerts (1997). Climates & Weather Explained.. Routledge (UK), p. 17. ISBN 0415125200. 
3. ^ 75th anniversary of starting aerological observations in Russia (Russian). EpizodSpace.

See also

• Atmospheric thermodynamics
• Ceiling balloon
• Global horizontal sounding technique
• Rocketsonde
• Sounding rocket