Weather Balloons: How These Low-Tech Tools Help Meteorologists Save Lives
By By Mark Leberfinger, AccuWeather.com Staff Writer
April 20, 2015, 6:06:22 AM EDT
In a high-tech world of satellites, computers, mobile devices and wearables, the weather balloon is still an important tool which helps meteorologists create more accurate forecasts that can help save lives and protect property, especially in the case of severe weather.
A radiosonde, an instrument that measures variables such as temperature and wind, is attached to the balloon, which is filled with helium, then launched into the atmosphere.
The earliest radiosondes were flown on kites, and it was in the 1930s when balloons were first used and tracked, Peter Ray, professor of Meteorology at Florida State University, said.
“Its unique capability, which no remote sensor can give, is high vertical resolution in temperature, relative humidity and even winds,” Ray said.
The down side is two-fold: The readings are in a quasi-vertical column or the path of the balloon, and there are only 91 National Weather Service weather balloon sites in the United States, Ray said.
“The data are used for assisting in the initial conditions for weather forecast models, combined with radar, satellite and other ground-based observations. Launches are done twice a day (23 UTC and 11 UTC) and are fed into the forecast models for the 00 UTC and 12 UTC model runs,” AccuWeather.com Meteorologist Brett Rathbun said.
This data are also used for local forecasting to help in determining the setup for severe thunderstorms, tornadoes, ice storms and more, Rathbun said.
“Typically, during the severe weather season, a 'cap' is observed in the lower levels of the atmosphere. A cap is a region in the lower levels of the atmosphere where temperatures increase with height,” he said. “This cap would prevent thunderstorms from developing if it is too strong. During the day, surface heating would weaken the cap.”
For locations with the potential for severe thunderstorms, special soundings may be launched during the day for updated information on the environmental conditions, Rathbun said.
“These are used to determine the strength of the cap and if thunderstorms may develop late in the day or if the cap will prevent any development. Radiosonde data can also determine the type of severe weather expected [squall line, tornadoes, etc.] based on the vertical wind pattern,” he said.
Despite any drawbacks, the radiosonde is the “gold standard” for accuracy and resolution for those points on its trajectory, Ray said. “All other methods smooth out the profile; they are all also subject to a variety of different errors."
“The best is what we have: a combination. Remote sensing gives coverage over the vast oceans, which the weather balloons cover poorly.”
Because air pressure decreases with increasing altitude, the latex balloon expands throughout the launch, Rathbun said.
“Once the balloon reaches the upper levels of the atmosphere, the balloon pops and the instrument begins its rapid descent back to the Earth's surface,” he said.
About 20 percent of the radiosondes are returned to the National Weather Service, Ray said.
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