Merging of ozone profiles from SCIAMACHY, OMPS and SAGE II observations to study stratospheric ozone changes
Authors: Arosio Carlo , Rozanov Alexei , Malinina Elizaveta , Weber Mark , Burrows John P. 
Published: April 2019

Abstract. This paper presents vertically and zonally resolved merged ozone time series
from limb measurements of the SCanning Imaging Absorption spectroMeter for
Atmospheric CHartographY (SCIAMACHY) and the Ozone Mapping and Profiler Suite
(OMPS) Limb Profiler (LP). In addition, we present the merging of the latter
two data sets with zonally averaged profiles from Stratospheric Aerosol and
Gas Experiment (SAGE) II. The retrieval of ozone profiles from SCIAMACHY and
OMPS-LP is performed using an inversion algorithm developed at the University
of Bremen. To optimize the merging of these two time series, we use data from
the Microwave Limb Sounder (MLS) as a transfer function and we follow two
approaches: (1) a conventional method involving the calculation of
deseasonalized anomalies and (2) a “plain-debiasing” approach, generally
not considered in previous similar studies, which preserves the seasonal
cycles of each instrument. We find a good correlation and no significant
drifts between the merged and MLS time series. Using the merged data set from
both approaches, we apply a multivariate regression analysis to study ozone
changes in the 20–50 km range over the 2003–2018 period. Exploiting
the dense horizontal sampling of the instruments, we investigate not only the
zonally averaged field, but also the longitudinally resolved long-term ozone
variations, finding an unexpected and large variability, especially at mid
and high latitudes, with variations of up to 3 %–5 % per decade at
altitudes around 40 km. Significant positive linear trends of about
2 %–4 % per decade were identified in the upper stratosphere between
altitudes of 38 and 45 km at mid latitudes. This is in agreement with
the predicted recovery of upper stratospheric ozone, which is attributed to
both the adoption of measures to limit the release of halogen-containing
ozone-depleting substances (Montreal Protocol) and the decrease in
stratospheric temperature resulting from the increasing concentration of
greenhouse gases. In the tropical stratosphere below 25 km negative
but non-significant trends were found. We compare our results with previous
studies and with short-term trends calculated over the SCIAMACHY period
(2002–2012). While generally a good agreement is found, some discrepancies
are seen in the tropical mid stratosphere. Regarding the merging of SAGE II
with SCIAMACHY and OMPS-LP, zonal mean anomalies are taken into consideration
and ozone trends before and after 1997 are calculated. Negative trends above
30 km are found for the 1985–1997 period, with a peak of −6 %
per decade at mid latitudes, in agreement with previous studies. The increase
in ozone concentration in the upper stratosphere is confirmed over the
1998–2018 period. Trends in the tropical stratosphere at 30–35 km
show an interesting behavior: over the 1998–2018 period a negligible trend
is found. However, between 2004 and 2011 a negative long-term change is
detected followed by a positive change between 2012 and 2018. We attribute
this behavior to dynamical changes in the tropical middle stratosphere.