Abstract
Abstract. High-quality satellite-based measurements are crucial to the assessment of global stratospheric composition change. The Stratospheric Aerosol and Gas Experiment II (SAGE II) provides the longest, continuous data set of vertically resolved ozone and aerosol extinction coefficients to date and therefore remains a cornerstone of understanding and detecting long-term ozone variability and trends in the stratosphere. Despite its stability, SAGE II measurements must be screened for outliers that are a result of excessive aerosol emitted into the atmosphere and that degrade inferences of change. Current methods for SAGE II ozone measurement quality assurance consist of multiple ad hoc and sometimes conflicting rules, leading to too much valuable data being removed or outliers being missed. In this work, the SAGE II ozone data set version 7.00 is used to develop and present a new set of screening recommendations and to compare the output to the screening recommendations currently used. Applying current recommendations to SAGE II ozone leads to unexpected features, such as removing ozone values around zero if the relative error is used as a screening criterion, leading to biases in monthly mean zonal mean ozone concentrations. Most of these current recommendations were developed based on “visual inspection”, leading to inconsistent rules that might not be applicable at every altitude and latitude. Here, a set of new screening recommendations is presented that take into account the knowledge of how the measurements were made. The number of screening recommendations is reduced to three, which mainly remove ozone values that are affected by high aerosol loading and are therefore not reliable measurements. More data remain when applying these new recommendations compared to the rules that are currently being used, leading to more data being available for scientific studies. The SAGE II ozone data set used here is publicly available at https://doi.org/10.5281/zenodo.3710518 (Kremser et al., 2020). The complete SAGE II version 7.00 data set, which includes other variables in addition to ozone, is available at https://eosweb.larc.nasa.gov/project/sage2/sage2_v7_table (last access: December 2019), https://doi.org/10.5067/ERBS/SAGEII/SOLAR_BINARY_L2-V7.0 (SAGE II Science Team, 2012; Damadeo et al., 2013).
Highlights
Even though the stratosphere contains less than 10 % of the mass of the atmosphere, changes in its chemical composition affect surface climate
We developed adequate Stratospheric Aerosol and Gas Experiment II (SAGE II) ozone datascreening rules using only three rules compared to up to 11 rules used in previous similar efforts that included screening used to produce homogenized ozone data sets (Davis et al, 2016; Hassler et al, 2018)
The new rules are simple and everything required to apply these rules is provided with the SAGE II data available from the NASA data centre (ASDC)
Summary
Even though the stratosphere contains less than 10 % of the mass of the atmosphere, changes in its chemical composition affect surface climate. Measurements from the Stratospheric Aerosol and Gas Experiment II (SAGE II, McCormick, 1987) remain a cornerstone of understanding and detecting long-term ozone variability and trends in the stratosphere This data set is recognized for its stability over its 21-year lifetime (1984–2005) and the high vertical resolution of its ozone and aerosol extinction coefficient measurements during its mission. A long-term, latitudinally and vertically resolved ozone database is required as input to climate models that do not have the ability to include a fully coupled stratospheric chemistry scheme (Hassler et al, 2018) Both Davis et al (2016) and Hassler et al (2018) applied around seven rules that are mainly based on previous studies by Wang et al (2002) with the modifications outlined in the SAGE II version 7.00 release notes. The expectation is that these new rules to SAGE II ozone data results in a more robust SAGE II ozone data set that can be used in trend analysis studies and homogenization efforts with other space-based measurements
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