GENEVA

Hundreds of high-flying balloons are genuine gatherers of climate information, the World Meteorological Organization (WMO) said Friday. 

“Weather balloons have been a very important part of the global observing network for decades as they are the primary source of data above the ground,” it said.

Computer forecast models which use weather balloon data are used by meteorological forecasters worldwide.

After the US shot down a Chinese balloon in its airspace, speculation about the balloons has accelerated.

WMO spokesperson Clare Nullis was asked about the phenomenon at a UN news conference. Her organization later released a statement on objects in space or high in the sky.

“Millions of observations are gathered worldwide every day: from space by over 50 satellites; from the ocean by 400 moored buoys, 1,250 drifting buoys and 7,300 ships; by 4 000 aircraft from around 40 commercial aircraft companies, and 10,000 automated and land-based observing stations, and by nearly 1,000 weather balloons equipped with radio-sondes,” said the WMO statement. “Radiosondes, which act as upper-air stations, are attached to free-rising balloons and released simultaneously from almost 900 locations worldwide.”

Between 100 and 200 stations make observations once every day.

“The balloon flights last for around 2 hours, making measurements of pressure, wind velocity, temperature, and humidity from just above the ground to heights of up to 35 km (22 miles),” it said.

They can travel many miles before they burst and fall back to Earth under a parachute.

Weather balloons provide valuable input in real-time for computer forecast models, local data for meteorologists to make forecasts and predict storms, climate monitoring, and data for research to better understand weather and climate processes. 

Made of natural rubber

Weather balloons are made of natural rubber or synthetic latex based on polychloroprene, according to the WMO.

Synthetic latex balloons have a much slower decomposition rate than natural rubber latex ones and the latter is preferred.

“Balloons are filled with either hydrogen or helium,” it said.

The sides are about 0.051 millimeters (0.002 inches) thick before release and will be only 0.0025 millimeters thick at typical bursting altitudes.

Their typical weight is 500 grams (1.1 pounds) but can vary from 10 grams to 3,000 grams, while their payload is up to 1,000 grams for the largest balloons.

On release, the balloons are less than 2 meters (6.56 feet) wide during ascent and the air pressure around the balloon decreases, allowing gas in the balloon to expand as they rise to about 6 meters in diameter.

“The radiosonde attached to the balloon will often endure temperatures as cold as -139 F (- 95C), relative humidities from 0% to 100%,” said the WMO.

“A transmitter on the radiosonde sends the data back to tracking equipment on the ground every one to two seconds. By tracking the position of the radiosonde, we can also calculate wind speed and direction,” it said.

A small battery powers the radiosonde.

In ocean areas, radiosonde observations are taken by about 15 ships, which mainly ply the North Atlantic, fitted with automated shipboard upper-air sounding facilities.

“There is constant research into improving radiosondes to ensure they can make accurate, consistent measurements,” said the WMO.