Multiple symptoms of total ozone recovery inside the Antarctic vortex during austral spring
Authors: Pazmiño Andrea , Godin-Beekmann Sophie , Hauchecorne Alain , Claud Chantal , Khaykin Sergey , Goutail Florence , Wolfram Elian , Salvador Jacobo , Quel Eduardo 
Published: May 2018

Abstract. The long-term evolution of total ozone column inside the Antarctic polar
vortex is investigated over the 1980–2017 period. Trend analyses are
performed using a multilinear regression (MLR) model based on various proxies
for the evaluation of ozone interannual variability (heat flux,
quasi-biennial oscillation, solar flux, Antarctic oscillation and aerosols).
Annual total ozone column measurements corresponding to the mean monthly values inside the
vortex in September and during the period of maximum ozone depletion from
15 September to 15 October are used. Total ozone columns from
the Multi-Sensor Reanalysis version 2 (MSR-2) dataset and from a combined record based
on TOMS and OMI satellite datasets with gaps filled by MSR-2 (1993–1995)
are considered in the study. Ozone trends are computed by a piece-wise
trend (PWT) proxy that includes two linear functions before and after the
turnaround year in 2001 and a parabolic function to account for the
saturation of the polar ozone destruction. In order to evaluate average total
ozone within the vortex, two classification methods are used, based on the
potential vorticity gradient as a function of equivalent latitude. The first
standard one considers this gradient at a single isentropic level (475 or
550 K), while the second one uses a range of isentropic levels between 400
and 600 K. The regression model includes a new proxy (GRAD) linked to the
gradient of potential vorticity as a function of equivalent latitude and
representing the stability of the vortex during the studied month. The
determination coefficient (R2) between observations and modelled values
increases by ∼ 0.05 when this proxy is included in the MLR
model. Highest R2 (0.92–0.95) and minimum residuals are obtained for the
second classification method for both datasets and months. Trends in September over the 2001–2017 period are statistically
significant at 2σ level with values ranging between 1.84 ± 1.03
and 2.83 ± 1.48 DU yr−1 depending on the methods and considered
proxies. This result confirms the recent studies of Antarctic ozone healing
during that month. Trends from 2001 are 2 to 3 times smaller than before the
turnaround year, as expected from the response to the slowly ozone-depleting
substances decrease in polar regions. For the first time, significant trends are found for the period of maximum
ozone depletion. Estimated trends from 2001 for the 15 September–15 October period over
2001–2017 vary from 1.21 ± 0.83 to 1.96 DU ± 0.99 yr−1 and
are significant at 2σ level. MLR analysis is also applied to the ozone mass deficit (OMD) metric for both
periods, considering a threshold at 220 DU and total ozone columns south of
60∘ S. Significant trend values are observed for all cases and
periods. A decrease of OMD of 0.86 ± 0.36 and 0.65 ± 0.33 Mt yr−1
since 2001 is observed in September and 15 September–15 October,
respectively. Ozone recovery is also confirmed by a steady decrease of the relative area
of total ozone values lower than 175 DU within the vortex in the
15 September–15 October period since 2010 and a delay in the occurrence of ozone levels
below 125 DU since 2005.