22 May 2023
 | 22 May 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

N2O as a regression proxy for dynamical variability in stratospheric trace gas trends

Kimberlee Dubé, Susann Tegtmeier, Adam Bourassa, Daniel Zawada, Douglas Degenstein, Patrick E. Sheese, Kaley A. Walker, and William Randel

Abstract. Trends in stratospheric trace gases like HCl, N2O, O3, and NOy show a hemispheric asymmetry over the last two decades, with trends having opposing signs in the Northern and Southern Hemispheres. Here we use N2O, a long-lived tracer with a tropospheric source, as a proxy for stratospheric circulation in the multiple linear regression model used to calculate stratospheric trace gas trends. This is done in an effort to isolate trends due to circulation changes from trends due to ozone depleting substances. We use measurements from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) and the Optical Spectrograph and InfraRed Imager System (OSIRIS), and model results from the Whole Atmosphere Community Climate Model (WACCM). Trends in HCl, O3, and NOy for 2004–2018 are examined. Using the N2O regression proxy, we show that observed HCl increases in the Northern Hemisphere are due to changes in the stratospheric circulation. We also show that negative O3 trends above 30 hPa in the Northern Hemisphere can be explained by change in the circulation, but that negative ozone trends at lower levels cannot. Trends in stratospheric NOy are found to be largely consistent with trends in N2O.

Kimberlee Dubé et al.

Status: open (until 03 Jul 2023)

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Kimberlee Dubé et al.

Kimberlee Dubé et al.


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Short summary
This paper presents a technique for understanding the causes of long-term changes in stratospheric composition. By using N2O as a proxy for stratospheric circulation in the model used to calculated trends it is possible to separate the effects of dynamics and chemistry on observed trace gas trends. We find that observed HCl increases are due to changes in the stratospheric circulation, as are O3 decreases above 30 hPa in the Northern Hemisphere.