Abstract
Abstract. For the past 17 years, the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument on the Canadian SCISAT satellite has been measuring profiles of atmospheric ozone. The latest operational versions of the level 2 ozone data are versions 3.6 and 4.1. This study characterizes how both products compare with correlative data from other limb-sounding satellite instruments, namely MAESTRO, MLS, OSIRIS, SABER, and SMR. In general, v3.6, with respect to the other instruments, exhibits a smaller bias (which is on the order of ∼ 3 %) in the middle stratosphere than v4.1 (∼ 2 %–9 %); however, the bias exhibited in the v4.1 data tends to be more stable, i.e. not changing significantly over time in any altitude region. In the lower stratosphere, v3.6 has a positive bias of about 3 %–5 % that is stable to within ±1 % per decade, and v4.1 has a bias on the order of −1 % to +5 % and is also stable to within ±1 % per decade. In the middle stratosphere, v3.6 has a positive bias of ∼ 3 % with a significant negative drift on the order of 0.5 %–2.5 % per decade, and v4.1 has a positive bias of 2 %–9 % that is stable to within ±0.5 % per decade. In the upper stratosphere, v3.6 has a positive bias that increases with altitude up to ∼ 16 % and a significant negative drift on the order of 2 %–3 % per decade, and v4.1 has a positive bias that increases with altitude up to ∼ 15 % and is stable to within ±1 % per decade. Estimates indicate that both versions 3.6 and 4.1 have precision values on the order of 0.1–0.2 ppmv below 20 km and above 45 km (∼ 5 %–10 %, depending on altitude). Between 20 and 45 km, the estimated v3.6 precision of ∼ 4 %–6 % is better than the estimated v4.1 precision of ∼ 6 %–10 %.
Highlights
It has been well established that prior to the implementation of the Montreal Protocol, global stratospheric ozone (O3) concentrations were declining on the order of approximately 5 % per decade (WMO, 2018)
The correlation coefficients are on the order of 0.8–0.9, and the standard deviations are on the order of 15 % (∼ 0.3 ppmv) in the upper stratosphere, 10 % (∼ 0.5 ppmv) in the middle stratosphere, and 20 % (0.1 ppmv) in the lower stratosphere
45 km the bias decreased slightly from 2 %–13 % to 2 %–11 % due to an improvement in the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) altitude registration, which is generated from measurements of the N2 continuum (Boone et al, 2020)
Summary
It has been well established that prior to the implementation of the Montreal Protocol, global stratospheric ozone (O3) concentrations were declining on the order of approximately 5 % per decade (WMO, 2018). Since 1997, after the implementation of the Montreal Protocol, stratospheric O3 concentrations are no longer declining, and the question remains, are O3 concentrations recovering? One type of uncertainty that needs to be properly characterized is the stability of systematic errors (drift) in the data. This is especially important when merging O3 data sets in order to produce a long-term data record on the order of decades.
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