Monsoons in the USA are increasingly breaking through into the stratosphere, a typically undisturbed layer of the atmosphere, introducing burning biomass and aerosols from western wildfires with potentially concerning consequences for the ozone layer and the climate.
A new study led by Dan Cziczo, a professor in the Department of Earth, Atmospheric, and Planetary Sciences in Purdue University’s College of Science, along with research scientist Xiaoli Shen, shows that these powerful summer storms can puncture into the stratosphere
Using high-altitude aircraft in collaboration with NASA, the team measured aerosols and particles inside the lower stratosphere during severe storm and wildfire seasons in the Midwestern United States.
Cziczo said: ‘In the summer, here in the Midwest particularly, we get all these air-quality warnings from wildfires because the climate is getting warmer and the land is getting drier. That’s becoming more common, but that’s all close to the planet’s surface, where we thought it was staying.
‘We flew this research aircraft up into the stratosphere, the next layer up of the atmosphere, which should be separate. Stratosphere means stratified; it should be separate. But what we found is that during these big wildfire seasons, the lower part of the stratosphere is just littered with these biomass particles.’
When moist air from the Gulf of Mexico collides with the Rocky Mountains, severe convective storms form across the Midwest and Great Plains, in a similar way to how monsoons form in the Indian subcontinent.
Ordinarily, the boundary between the troposphere (the layer of atmosphere closest to Earth’s surface) and the stratosphere acts like a roof. These severe storms can push up toward it, but rarely penetrate it.
However, this research finds that some storms develop “overshooting tops” so powerful they break through into the stratosphere, carrying not just water vapour and ice, but also smoke, aerosols and biomass-burning particles. The result is that was considered a pristine region of the atmosphere is now being altered.
Cziczo warns: ‘This could be a really big deal for a number of reasons. For one thing, for so long, we’ve assumed the stratosphere is a pristine area. But what this shows is that human impacts through a changing climate can affect the chemistry and the radiative ability of the stratosphere.
‘These particles can interact with sunlight and heat up, warm the stratosphere. It could affect its stability — which is vital to the planet.’
While the research does not yet quantify the full long-term risk to the ozone layer or global climate, it highlights a previously under-appreciated pathway by which wildfires and storm systems may reach far into the upper atmosphere. As wildfire seasons lengthen, and storms intensify under a warming climate, the implications for stratospheric chemistry and Earth’s protective layers could grow.
The research can be accessed here.
Photo: Matteo Fusco
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