By Sabin Russell
Intrepid weather balloonists at Berkeley Lab have unintentionally achieved stratospheric heights in their quest to develop a cheap and reliable system to track layers of soot in the atmosphere.
A four-foot latex balloon launched from the Lab last month soared as planned seven miles into the morning skies, into the lower reaches of the stratosphere. That was the goal of this early test flight, but the balloon seemed to have a mind of its own: It climbed another five miles, where its camera caught the dark edges of space arcing above.
I last wrote about the ups and downs of this fascinating and frankly fun research project in April. It has a serious goal of gathering hard-to-get data on the fingers of sooty particles that blow through the skies and exert complex effects on weather and climate. Sometimes these pollutants from power plants, diesel engines, and wildfires help to heat up and dry out the atmosphere; and sometimes they block sunlight and cool temperatures down.
The team led by Environmental Energy Technologies Division climate scientist Thomas Kirchstetter and atmospheric chemist Odelle Hadley carried out this first long-distance test flight of their sensor-packed weather balloon on the morning of July 27.
Satellite instruments can probe a column of air to assess layered soot concentrations, but the data are not dependable. Aircraft can carry instruments to measure much more accurately, but plane flights are far too expensive, particularly if measurements are to be collected for many years. Weather balloons, on the other hand, can be purchased on-line for about $35 each, and will fly with the winds for about $100 worth of helium.
The balloon and its five-pound package, which included two on-board digital video cameras, was released at 8 a.m. from the new parking lot at the site of the recently removed Bevatron, the old atom-smasher that helped four Berkeley Lab scientists win Nobel prizes. “Not likely to win as many for this project,” Kirchstetter deadpanned. The goal was to reach 12 kilometers (7.2 miles), at which point the instrument package would be cut loose by a small charge and would descend by an umbrella-sized parachute to a field near Winters, California, just west of Davis.
The balloon release was flawless, and despite a tense moment when it looked like the package could snag in one of the great eucalyptus giants that ring Berkeley Lab, it rose freely and headed northeast. Almost two hours into the flight, five miles over the Delta town of Fairfield, the chase team driving up the I-80 corridor suddenly lost contact with the GPS transponder inside the Styrofoam instrument case. But the balloon was still sailing along, on course and sending temperature and altitude data via satellite link.
Then, seven miles over the farm fields of Winters, things got dicey. After five previous low-altitude tests where it worked like a charm, the cut-down charge failed at its appointed hour. The balloon and package kept on soaring, into the stratosphere. “If the balloon had reached equilibrium, and caught the jet stream, it could have gone all the way to Africa,” says Hadley. Instead — as anticipated in Plan B — the ever-expanding helium-filled balloon kept rising and simply popped, 12 miles (20 km) above rice fields near Yuba City. During those tense two extra hours, the GPS system mysteriously came to life. That eased the task of the chase team: Instrument designer Danny Wilson, who is a Berkeley Lab researcher and UC Berkeley PhD student; and summer interns Areidy Beltran, Jacob Schneider-Martin, and Allen Boltz. Schneider-Martin will be a senior this fall at Berkeley High, where Boltz teaches chemistry. They followed the revived GPS signal, and about an hour after it had landed, they found the package safe and sound in a Sacramento Valley farm field, just a few yards from an irrigation ditch.
Now the team is evaluating the flight; to find out why the GPS device temporarily failed (cold battery?) and why the cut-and-release charge didn’t fire (moisture?). On this flight, the package transmitted data that tracked temperature, relative humidity, and altitude — the same sort of information gathered every day by weather balloon radiosondes launched by the National Weather Service. Left off this test flight was the package of custom-built electronics called an Aethalometer™ that will perform the actual measurements of black carbon. A miniaturized version of a device invented a decade ago by scientists at Berkeley Lab, it is a highly sensitive instrument that sucks air past a filter through which an LED light source shines. A sensor measures the dimming of the light to calculate the concentrations of soot over time. Each one costs about $8,000. “We could not afford to lose it on our first long-distance flight,” said Hadley.
Once the team has full confidence in its release, chase, and retrieve system, the scientists plan to start launching a series of data-gathering flights with the soot detector aboard. Short term, their goal is to compare their reliable balloon-flight findings with sensor data from satellites. With enough flights, they hope to characterize accurately the complex layers of soot to understand how they affect weather and climate patterns. Long-term, they hope to prove that this inexpensive system could piggyback on those daily National Weather Service balloon flights and build a dynamic nationwide portrait of the skies.
In this and all of these future balloon flights, there is no need to reach for the stratosphere. The varied sooty layers of most scientific interest lie in the troposphere, that seven mile column of sky where most of our weather occurs — and where better-behaved balloons are supposed to fly.
Since this blog post was written, the team has conducted another launch from the Bevatron site. This time the aethalometer was aboard. The balloon traveled about 40 miles and the package cut loose as planned, five miles above fields near Rio Vista. It landed in a goat pasture, and was safely retrieved by the LBNL chase team, which is now evaluating the data.
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