“When commercial airplanes break through the clouds to reach cruising altitude, they have typically arrived in the stratosphere, the second layer of Earth’s atmosphere. The air up there is dry and clear, and much calmer than the turbulent atmosphere we experience on the ground.
And yet, for all its seeming tranquility, the stratosphere can be a powerful conveyor belt, pulling air up from the Earth’s equatorial region and pushing it back down toward the poles in a continuously circulating pattern. The strength of this circulation can significantly impact the amount of water vapor, chemicals, and ozone transported around the planet.
Now scientists in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) have for the first time determined the strength of the stratosphere’s circulation, based on observations of key chemicals traveling within this atmospheric layer.
In a paper published today in the journal Nature Geoscience, the team reports that the stratosphere pulls about 7 billion kilograms of air up through the tropics per second, worldwide, at an altitude of about 20 kilometers. The researchers estimate that the average parcel of air can spend about 1.5 years within this layer before circulating back down to lower layers of the atmosphere.
The new estimate can help scientists gauge where and for how long water vapor, ozone, and greenhouse gases remain within the stratosphere. Scientists can also use the team’s method to determine future changes in the stratosphere’s strength — essential information for tracking the recovery of the ozone hole and the progression of global warming.
The paper’s lead authors are Marianna Linz, a former PhD student in EAPS who is now a postdoc at the University of California at Los Angeles; and Alan Plumb, a professor emeritus in EAPS; along with researchers from New York University, Karlsruhe Institute of Technology, the National Center for Atmospheric Research, Cambridge University, and Caltech.”