Abstract
Abstract. The ozone profile records of a large number of limb and occultation satellite instruments are widely used to address several key questions in ozone research. Further progress in some domains depends on a more detailed understanding of these data sets, especially of their long-term stability and their mutual consistency. To this end, we made a systematic assessment of 14 limb and occultation sounders that, together, provide more than three decades of global ozone profile measurements. In particular, we considered the latest operational Level-2 records by SAGE II, SAGE III, HALOE, UARS MLS, Aura MLS, POAM II, POAM III, OSIRIS, SMR, GOMOS, MIPAS, SCIAMACHY, ACE-FTS and MAESTRO. Central to our work is a consistent and robust analysis of the comparisons against the ground-based ozonesonde and stratospheric ozone lidar networks. It allowed us to investigate, from the troposphere up to the stratopause, the following main aspects of satellite data quality: long-term stability, overall bias and short-term variability, together with their dependence on geophysical parameters and profile representation. In addition, it permitted us to quantify the overall consistency between the ozone profilers. Generally, we found that between 20 and 40 km the satellite ozone measurement biases are smaller than ±5 %, the short-term variabilities are less than 5–12 % and the drifts are at most ±5 % decade−1 (or even ±3 % decade−1 for a few records). The agreement with ground-based data degrades somewhat towards the stratopause and especially towards the tropopause where natural variability and low ozone abundances impede a more precise analysis. In part of the stratosphere a few records deviate from the preceding general conclusions; we identified biases of 10 % and more (POAM II and SCIAMACHY), markedly higher single-profile variability (SMR and SCIAMACHY) and significant long-term drifts (SCIAMACHY, OSIRIS, HALOE and possibly GOMOS and SMR as well). Furthermore, we reflected on the repercussions of our findings for the construction, analysis and interpretation of merged data records. Most notably, the discrepancies between several recent ozone profile trend assessments can be mostly explained by instrumental drift. This clearly demonstrates the need for systematic comprehensive multi-instrument comparison analyses.
Highlights
Long-term global observations of the distribution and evolution of ozone are vital to improve our current understanding of atmospheric processes, and thereby to allow more robust projections of the recovery of the ozone layer and climate change
Profile data from alternative viewing geometries were not investigated either, and their quality may well be different from the findings presented in the following
We mention some indicators of the performance of the ground networks for this type of analysis: (a) the smallest value of the 1 σ regression uncertainty found across the network, (b) the typically found uncertainty and (c) the adjustment factor κ
Summary
Long-term global observations of the distribution and evolution of ozone are vital to improve our current understanding of atmospheric processes, and thereby to allow more robust projections of the recovery of the ozone layer and climate change. Measurements of the vertical profile of ozone have been carried out over the last few decades by a large number of instruments, operating in situ or from remote vantage points, on the ground and in space (for an overview, see Hassler et al, 2014) These indisputably show globally declining ozone levels during the 1980s and a large part of the 1990s in the lower and upper stratosphere (∼ 5–7 % decade−1), and to a lesser extent in the middle stratosphere (1– 2 % decade−1) (WMO, 2014; Harris et al, 2015). The observed loss rates are in excellent agreement with expectations for the chemical destruction of ozone by manmade halocarbons (WMO, 2014) The abundances of these substances have decreased significantly over the past 15– 20 years (WMO, 2011), as a result of the Montreal Protocol and its subsequent adjustments and amendments. Shedding more light on the latter issue is the main objective of this paper
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