Chaos theory in the atmosphere
Researchers map the paths particles take. Nick Carne reports.
Hungarian researchers say they have used chaos theory to produce maps for predicting the paths of particles emitted into the atmosphere.
Writing in the American Institute of Physics journal Chaos, Tímea Haszpra from Eötvös Loránd University describes combining wind data with the known behaviour of air particles in the atmosphere to determine how pollutants and volcanic ash will travel.
That would be worth knowing. Particles from industrial accidents have the potential to travel full hemispheres before falling to the ground, and the risk of ash reaching the stratosphere is well known to anyone who’s had a flight delayed after a volcano.
"One of the most surprising parts of the research is the wide range of individual lifetimes," Haszpra says.
"Lifetimes ranged from about two to 150 days for typical volcanic ash particles. More than 10% of smaller particles survive in the atmosphere as much as one year, and more than 1% survive two years."
Atmospheric particle motion exhibits fractal-like behaviour, Haszpra says, and when data is specially filtered, an object that governs chaotic particle motion and is called a chaotic saddle can be found.
The paths of each simulated particle show properties that are transiently brought together by the changes in the flow of the atmosphere, akin to sitting on the saddle, before falling off the saddle and, consequently, falling to Earth.
In general, Haszpra and a colleague found that particles coming from the area around the equator remain in the atmosphere for the longest time, and particles smaller than one micron could stay in the atmosphere for years before falling.
They also found that particles in one area of a map could be in the air up to 10 times as long as particles nearby on the map. How these lifetimes were distributed around the globe varied depending on the season.
To illustrate the concepts in the paper, Haszpra has created an online game called RePLaT-Chaos, which lets players learn the topic of atmospheric advection by creating and testing their own volcanic eruptions.
She hopes the findings can inform future efforts to use sun-reflecting air particles to counteract climate change.
She says she plans to expand on this work by incorporating historical meteorological data and climate models to better understand how the dispersion of particles might change when the climate changes.