20 years of ClO measurements in the Antarctic lower stratosphere

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We present 20 years of springtime measurements of ClO over Antarctica from the Chlorine monOxide Experiment (ChlOE1) ground-based millimeter wave spectrometer at Scott Base, Antarctica, as well 12 years of ClO measurements from the Aura Microwave Limb Sounder (MLS). From August onwards we observe a strong increase in lower stratospheric ClO, with a peak column amount usually occurring in early September. From mid-September onwards we observe a strong decrease in ClO. In order to study interannual differences we focus on a 3-week period from August 28 to September 17 for each year, and compare the average column ClO anomalies. These column ClO anomalies are shown to be highly correlated with the average ozone mass deficit for September and October of each year. We also show that anomalies in column ClO are anti-correlated with 30 hPa temperature anomalies, both on a daily and an interannual timescale. We calculate the dependence of interannual variations in column ClO on interannual variations in temperature. By making use of this relationship we can better estimate the underlying trend in the Cly which provides the reservoir for the ClO. The resultant trends for zonal MLS, Scott Base MLS (both 2004–2015), and ChlOE (1996–2015) were 0.5 ± 0.2 %/yr, −1.4 ± 0.9 %/yr, and −0.6 ± 0.4 %/yr, respectively. These trends are within 1σ of trends in stratospheric Cly previously found at other latitudes. This decrease in ClO is the result of changes in anthropogenic CFC emissions due to actions taken under the Montreal Protocol.




Nedoluha, G. E., Connor, B. J., Mooney, T., Barrett, J. W., Parrish, A., Gomez, R. M., … Santee, M. L. (2016). 20 years of ClO measurements in the Antarctic lower stratosphere. Atmospheric Chemistry and Physics, 16(16), 10725–10734. https://doi.org/10.5194/acp-16-10725-2016

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