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Speaker: Aaron Match, New York University

Title: Understanding the ozone response to global warming

Abstract: Over the past two decades, the ozone layer has begun to recover from ozone-depleting substances. At the same time, chemistry-climate models suggest that global warming will generally increase ozone, due to stratospheric cooling, except in the tropical lower stratosphere, where ozone is reduced by tropospheric warming. There are competing explanations for these reductions. In a first family of explanations, the ozone reductions are argued to result from strengthening of the Brewer-Dobson circulation, which upwells ozone-poor air from below. A second family of explanations assumes that tropospheric expansion directly shifts the ozone profile upwards. As such, tropopause-following coordinates are used to remove global warming trends. Yet, on physical grounds, tropospheric expansion is not expected to lead directly to an upward shift of the ozone profile, but rather to an upward shift in the tropospheric destruction of ozone, which takes a “bite” out of the stratosphere, the low ozone anomalies from which are then advected upwards. An idealized model of ozone photochemistry and transport reveals that strengthening upwelling and tropospheric expansion both contribute at leading order to reducing ozone in the tropical lower stratosphere under global warming. Tropopause-following coordinates are found to not generally remove the effects of tropospheric expansion.

Brief bio: Dr. Aaron Match is an NSF Postdoctoral Research Fellow in Atmospheric and Geospace Sciences working with Professor Edwin Gerber at New York University. Dr. Match received his Ph.D. in 2021 from the Program in Atmospheric and Oceanic Sciences at Princeton University under the supervision of Professor Stephan Fueglistaler, with a thesis entitled, “The Unified Internal Dynamics and External Interactions of the Quasi-Biennial Oscillation”. Dr. Match conducts climate science outreach with Climate Up Close.