Radiosonde

A GPS sonde, approx 220 × 80 ×75 mm (8.7 × 3.1 × 3 in) (with grounding station in background, used to perform a 'ground check' and also recondition the humidity sensor)

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 only measure wind speed and direction. Colloquially, rawinsondes are usually referred to as radiosondes.

Modern radiosondes measure or calculate the following variables:

• Pressure
• Altitude
• Geographical position (Latitude/Longitude)
• Temperature
• Relative humidity
• Wind (both wind speed and wind direction)
• Cosmic ray readings at high altitude

Radiosondes measuring ozone concentration are known as ozonesondes.

History

Kites used to fly a meteograph

Meteograph used by the US Weather Bureau in 1898

The first flights of aerological instruments was done in the second half of the XIX century with kites and meteographs, a recording device measuring pressure and temperature that was recuperated after the experiment. This proved to be difficult because the kites were linked to the ground and were very difficult to manoueuvrer in gusty conditions. Furthermore, the sounding was limited to low altitudes because of the link to the ground.

Gustave Hermite and Georges Besançon, from France, were de first in 1892 to use a balloon to fly the meteograph. In 1898, Léon Teisserenc de Bort organized at the Observatoire de Météorologie Dynamique de Trappes the first regular dayly use of these balloons which lead him to notice that the temperature lower with height up to a certain latitude, varying with seasons, and then stabilize and raise afterward. This is the discovery of the tropopause and the stratosphere which he announce in 1902 at the French Academy of Sciences. Other researchers, like Richard Aßmann and William Henry Dines, were working at the same times with similar instruments.

In 1924, Colonel William Blaire in the U.S. Signal Corps did the first primitive experiments with weather measurements from balloon, making use of the temperature dependence of radio circuits. The first true radiosonde that sent precise encoded telemetry from weather sensors was invented in France by Robert Bureau. Bureau coined the name "radiosonde" and flew the first instrument on January 7, 1929. Developed independently a year later, Pavel Molchanov flew a radiosonde on January 30, 1930. Molchanov's design became a popular standard because of its simplicity and because it converted sensor readings to Morse code, making it particularly easy to use without special equipment or training.

Working with a modified Molchanov sonde, Sergey Vernov was the first to use radiosondes to perform cosmic ray readings at high altitude. On April 1, 1935, he took measurements up to 13.6 km (8.5 mi) using a pair of Geiger counters in an anti-coincidence circuit to avoid counting secondary ray showers. This became an important technique in the field, and Vernov flew his radiosondes on land and sea over the next few years, measuring the radiation's latitude dependence caused by the Earth's magnetic field.

In 1985, as part of the Soviet Union's Vega program, the two Venus probes, Vega 1 and Vega 2, each dropped a radiosonde into the atmosphere of Venus. The sondes were tracked for two days.

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 100 to 3,000 g (3.5 to 105.8 oz). 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 g (28 oz) balloon will burst at about 21 km (13 mi). One radiosonde from Clark Air Base, Philippines reached an altitude of 155,092 ft (47,272 m). At that time the United States Air Force was not logging such records.

The modern radiosonde communicates via radio with a computer that stores all the variables in real-time. The first radiosondes were observed from the ground with a theodolite, and gave only a wind estimation by the position. With the advent of radar by the Signal Corps it was possible to track the balloons with the SCR-658 radar. Modern radiosondes can use a variety of mechanisms for determining wind speed and direction, such as a radio direction finder or GPS. The weight of a radiosonde is typically 250 g (8.8 oz). It should also be noted that the average radiosonde is lost and never recovered; however, for the more expensive instrument packages, balloon-borne unmanned gliders (or UAVs) are used to ensure recovery.

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 45 minutes before the official observation time of 0000 UTC and 1200 UTC, so as 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 Appendix C, U.S. Land-based Rawinsode Stations of the Federal Meteorological Handbook #3, titled Rawisonde and Pibal Observations, dated May 1997.

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.

This process was also used to collect data in the lower atmosphere. The National Severe Storms Laboratory (NSSL) in Norman, OK used radiosonde data to better understand and predict tornadic activity. Release stations were manned during the height of the tornado season around Oklahoma City, OK in March and April each year. Routine balloon launches were done to collect atmospheric data when conditions indicated a chance of a large storm event. The ultimate goal was have a radiosonde equipped balloon drawn into the developed tornado providing pressure and temperature data to the tracking crew at the launch site. This data would then be sent to the NSSL for analysis.

See also

• 6AK5
• Aerography (meteorology)
• Atmospheric model
• Atmospheric thermodynamics
• Ceiling balloon
• Global horizontal sounding technique
• Rocketsonde
• Sonde (electronics)
• Sounding rocket
• Totex
• Vilho Väisälä
• Vaisala
• Water-activated battery

External links

• Upper air data for the world - past and present
• WMO spreadsheet of all Upper Air stations around the world
• Interpreting radiosonde data Tephigrams and Skew-T log P diagrams.
• Radiosonde Sounding System at webmet.com
• NOAA National Weather Service Radiosonde Factsheet
• Sergei Nikolaevich Vernov
• SCR-658 pics
• early pics