Up and away: Launching a weather balloon
By Joy Moses-Hall
Sunday, April 15, 2018
The April breezes that follow March freezes are just teases for a balloon to wander where it pleases.
To put it in the terms of a homework problem, If a weather balloon leaves Catawba Valley Community College at 9 a.m. on Saturday, where will the payload land?
It’s not a fruitless problem. Every day about 800 weather balloons are launched from meteorological stations around the world, lifting instruments high up into the atmosphere: higher than clouds, higher than jets, higher than most of the air, taking measurements as they go to aid in weather predictions that help us figure out where balloons will fly.
A balloon’s journey is a three-dimensional puzzle, because the balloon does not just go straight up and straight down. It can and does get caught in strong winds, possibly blowing the balloon hundreds of miles in any direction. Its ultimate position depends on how much time it spends in the fastest winds.
The vertical journey also contributes to where it lands. The vertical journey is all about buoyancy. Like the oil bobbing up in salad dressing, a balloon filled with helium is lighter than air, floating up to the top of the sky. The more helium in the balloon, the faster it floats up. But helium fills a double-edged gas bladder. Extra helium juices the vertical flight, but also cuts it short. Extra helium fattens the balloon from the very start, leaving it less room to expand in the diminished atmosphere above before bursting like a bubble in uncorked champagne.
The instrument package tagging along with the balloon holds it back. Every gram of wizardry going up adds another dollop of helium to the starting girth, and sacrifices a few feet of altitude.
A few feet of altitude was all that Larry Walters sought when he secured 45 weather balloons to his lawnchair in 1982, and lifted off with a beer, a sandwich, and a pellet gun, beating Pixar to a punchline. His plan was to float at treetop level for a few hours in his California neighborhood. His surprising reality launched him a nonstop three miles up, where temperatures are around 0 degrees and sandwiches freeze. He drifted through LAX airspace and blacked out a Long Beach community after he shot out some balloons and dragged a tether across the power lines.
Unlike recreational riders, instrument payloads rely on a balloon’s planned obsolescence at the 1 percent atmosphere, about 100,000 feet. The balloon, stretched to capacity, ruptures 19 miles overhead. The payload descent, fast and guided by the small parachute, begins. Radio and GPS transmitters on board continue to emit pings like smoke rings of radar, broadcasting the three dimensional position once or more every minute.
Things fall from the sky all the time. Meteorites, bits of Mars, space junk, airplanes. The terrible tragedy of a small plane crash an hour from our home in New York State in the 1970s was a hiking opportunity to view a piece of solemn history. So we hiked. As teenagers, my brother and I whined as Dad led us into the woods from a country road. Out in the middle of nowhere’s nowhere, heading for who knew what, wandering without conviction. Wasted effort. Wasted time. Wasted essence.
Until all of a sudden the waste lay bare before our eyes. An errant cushion. A scrap of metal. A wheel. A pall, invisible but rigid, drew tightly around the wreckage. An upside-down seat, even after a year’s worth of leaves had feathered the shards: what essence had sat there? With what happy enthusiasm had the journey begun? With what horror had failure loomed? A crisp autumn nothing day crystallized around the sudden sad sweep of fate that befell the plane’s occupants. We stood around the propeller, wordless. Dad reached down, lifted the propeller, hoisted it onto his shoulders, trudged out of the forest, and later mounted it on the wall of his classroom.
Perhaps we can imagine that the plane crash would not have happened in more modern times because of better forecasting, better positioning information, better payloads. Even when they go silent, and find their own nowhere to land, the nature of humans to innovate and grow is bettered by the efforts of little payloads.
The Pitt Community College payload that launched from Catawba went silent on the way down. After rising to 93,000 feet — unofficially higher than the other five community college balloons — it went off the grid at 60,000 feet west of Greensboro. None of the tracking devices on board has been heard from since, but it was found a few days later in a backyard northwest of Durham. Now the data crunching begins. Another homework problem.
Follow @jmoseshall on Facebook. Joy Moses-Hall teaches physics and astronomy at Pitt Community College. She has a PhD in oceanography and is the author of the novel Wretched Refuge.