Background on Driftsondes

September 2006

What is a driftsonde?
It’s a new type of observing system that shows great promise in tracking weather above hard-to-reach parts of the globe, such as the remote Pacific and Atlantic oceans. A driftsonde consists of a large balloon (roughly 30 feet tall), a device that sends and receives radio signals, and a gondola to hold instrument packages that descend by parachute. This summer NCAR and the French space agency (CNES) collaborated to launch the first driftsonde ever used in a weather research project. In this partnership, CNES was responsible for the balloon system and NCAR developed the gondola and instrument packages.

How does a driftsonde work?
The special type of balloon used in the driftsonde ascends to the lower stratosphere, at heights of around 60,000 to 65,000 feet. It can remain airborne for a week or longer, drifting with the winds that prevail at these altitudes. Scientists at an operations center communicate with the driftsonde through Iridium communications satellites. With a remote command, they can release one of the instrument packages, which is called a dropsonde. The dropsonde falls through the atmosphere, collecting weather data twice per second and sending the data back to the driftsonde gondola. Later, the information is relayed to the operations center and then on to forecast centers.

Why are driftsondes only now being used for weather research?
The idea for driftsondes was first conceived in the early 1970s, and several tests were conducted in subsequent years. However, the power and communication technologies were insufficient at the time, and the instruments were relatively bulky and heavy, requiring expensive balloons to loft them. In the last few years, miniaturized electronics have reduced the size, weight, and power required for driftsonde instruments, and GPS-based communications have become standard. The new technology is also more durable in the stratosphere’s extreme cold.

What’s next for the driftsonde?
The use of driftsondes for hurricane genesis was made possible by two major studies: THORPEX (The Observing System Research and Predictability Experiment), a 10-year program under the World Meteorological Organization designed to accelerate skill in predicting high-impact weather events, and AMMA (the African Monsoon Multidisciplinary Analysis), a multiyear program designed to advance understanding of the West African monsoon. The next major deployment of driftsondes in THORPEX will be for an Antarctic climate-change study in association with the International Polar Year (2007-08) and  a North Pacific campaign in 2008 focused on predicting intense winter cyclones, floods, severe thunderstorm outbreaks, and fire weather over North America.

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