MIT graduate student Aditi Sheshadri's research on the impacts of stratospheric warming events on the lower atmosphere garnered her an award at the American Meteorological Society's 18th Conference on the Middle Atmosphere.
Aditi Sheshadri, a graduate student in MIT’s Program in Atmospheres, Oceans, and Climate, is a recipient of the American Meteorological Society’s (AMS) Best Student Presentation Award for her research on the impacts of stratospheric warming events on the lower atmosphere, which she presented at the 18th Conference on the Middle Atmosphere. Sheshadri is one of only three students to win the award at this year’s conference.
“I was surprised I won this award; it was unexpected,” she said. “But it’s great.”
A member of Professor of Meteorology Alan Plumb’s group, Sheshadri researches stratospheric circulation variability. “[Aditi] especially focuses on the dramatic collapse of westerly winds that occur during sudden stratospheric warmings and final warmings in the northern and southern hemisphere, which have implications for surface climate,” Plumb said.
In the study presented at AMS, Sheshadri investigated the behavior of stratospheric polar vortices—large cyclonic flows that form and decay seasonally. These vortices reach their maximum strength by mid-winter when the polar stratosphere is coldest, and break up during warmer seasons.
About every other year, the Arctic polar vortex in the northern hemisphere collapses in the middle of winter, when it should be strongest. This causes temperatures in the stratosphere over this cold region to increase by up to 50 degrees in a week. “These are pretty extreme events,” she said. “And result in persistent perturbations to surface weather and winds for up to two months after collapse.”
To figure out the conditions under which this happens, Sheshadri modeled how the vortex’s seasonal behavior changed in response to the amount of wave forcing from the troposphere—the lowest layer of Earth’s atmosphere where all weather occurs. She found that the stratosphere’s seasonal cycle has a continuous impact on the troposphere, even if the troposphere doesn’t have a seasonal cycle of its own.“[From the model] we were able to recover how the northern and southern hemisphere polar vortices behave in the real atmosphere, which is cool,” Sheshadri said. “We also looked at whether the stratosphere has memory.”
In other words, if a polar vortex collapses this winter, is it more likely to happen again next year or was it a random event? “We found that in the real atmosphere there might possibly be some evidence of memory, but in the model these events appear to happen at random with a given probability,” she said.
Sheshadri continues to study polar vortex variability—particularly the impact of the ozone hole on the Antarctic polar vortex, its’ subsequent impacts on Southern Hemisphere surface climate, and eddy-mean flow feedbacks in the stratosphere. The work is published in the Journal of Atmospheric Sciences.