Exceptionally Low Arctic Stratospheric Ozone in Spring 2020 as Seen in the CAMS Reanalysis

Abstract

A reanalysis data set produced by the Copernicus Atmosphere Monitoring service (CAMS reanalysis, 2003 to present day) augmented by ERA5 data for the years before 2003 is used to describe the evolution of the 2020 Arctic ozone season and to compare it with years back to 1979. Ozone columns over large parts of the Arctic reached record low values in March and April 2020 because of an exceptionally strong, cold, and persistent Arctic polar vortex. Minimum ozone columns were below 250 DU for most of March and the first half of April, with the lowest values of 211 DU in the CAMS reanalysis found on 18 March. Such low values are extremely unusual for the Arctic. The previous years with similarly strong Arctic ozone depletion were 2011 and 1997 with minimum values of 232 and 217 DU, respectively. The performance of the CAMS ozone analysis is assessed by comparison with ozonesonde data and found to agree well with the independent observations. We find a clear sign of chemical ozone destruction with ozone severely depleted in a layer between 80 and 50 hPa in late March and early April when partial pressure values below 2 mPa were observed. Profiles from the limb sounders Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer (ACE‐FTS) and Microwave Limb Sounder (MLS) show clear signs of chlorine activation and the presence of polar stratospheric clouds. Monthly mean ozone columns in March 2020 were up to 180 DU or 40% lower than the CAMS climatology (2003–2019) while values for 2011 and 1997 were lower by 31% and 35%, respectively.

The Unusual Stratospheric Arctic Winter 2019/20: Chemical Ozone Loss From Satellite Observations and TOMCAT Chemical Transport Model

“…The Arctic winter/spring 2019/20 is one of the coldest on record (Dameris et al., 2021; Inness et al., 2020; Lawrence et al., 2020) with temperatures sufficient for PSC occurrence from November until April. The PSC volume was at a record high (based on available observations) in November and from late February throughout March, which indicates substantial polar ozone loss.…”

“…In February 2020, the 100 hPa eddy heat flux reached the lowest value since 1980, which may have been responsible for setting record high PSC volumes starting by the end of February 2020. Both the continuous low dynamical activity, also linked to the positive Further details on the stratospheric meteorology in this particular winter and comparisons to past winters can be found in this journal's special issue and other studies (Dameris et al, 2021;Inness et al, 2020;Lawrence et al, 2020;Manney et al, 2020).…”

“…Further details on the stratospheric meteorology in this particular winter and comparisons to past winters can be found in this journal's special issue and other studies (Dameris et al., 2021; Inness et al., 2020; Lawrence et al., 2020; Manney et al., 2020).…”

“…Both the continuous low dynamical activity, also linked to the positive anomaly in the Arctic Oscillation (Lawrence et al, 2020), and very low stratospheric temperatures contributed to the very low ozone in Arctic winter 2019/20. Further details on the stratospheric meteorology in this particular winter and comparisons to past winters can be found in this journal's special issue and other studies (Dameris et al, 2021;Inness et al, 2020;Lawrence et al, 2020;Manney et al, 2020).…”

“…The polar minimum total ozone evolved in a very similar way to the mean (Figure 3b). A first record minimum was observed in March 2011 and this record was broken again in March 2020 with total ozone being slightly below 220 DU for a brief period (Inness et al., 2020; Wohltmann et al., 2020), a value which commonly defines the boundary of the Antarctic ozone hole (e.g., NASA Ozone Watch, 2020). The steady decline in minimum ozone in polar winter is considered a good proxy for continued polar chemical ozone loss (Müller et al., 2008).…”