Overview and update of the SPARC Data Initiative: comparison of stratospheric composition measurements from satellite limb sounders

Abstract

Abstract. The Stratosphere-troposphere Processes and their Role in Climate (SPARC) Data Initiative (SPARC, 2017) performed the first comprehensive assessment of currently available stratospheric composition measurements obtained from an international suite of space-based limb sounders. The initiative's main objectives were (1) to assess the state of data availability, (2) to compile time series of vertically resolved, zonal monthly mean trace gas and aerosol fields, and (3) to perform a detailed intercomparison of these time series, summarizing useful information and highlighting differences among datasets. The datasets extend over the region from the upper troposphere to the lower mesosphere (300–0.1 hPa) and are provided on a common latitude–pressure grid. They cover 26 different atmospheric constituents including the stratospheric trace gases of primary interest, ozone (O3) and water vapor (H2O), major long-lived trace gases (SF6, N2O, HF, CCl3F, CCl2F2, NOy), trace gases with intermediate lifetimes (HCl, CH4, CO, HNO3), and shorter-lived trace gases important to stratospheric chemistry including nitrogen-containing species (NO, NO2, NOx, N2O5, HNO4), halogens (BrO, ClO, ClONO2, HOCl), and other minor species (OH, HO2, CH2O, CH3CN), and aerosol. This overview of the SPARC Data Initiative introduces the updated versions of the SPARC Data Initiative time series for the extended time period 1979–2018 and provides information on the satellite instruments included in the assessment: LIMS, SAGE I/II/III, HALOE, UARS-MLS, POAM II/III, OSIRIS, SMR, MIPAS, GOMOS, SCIAMACHY, ACE-FTS, ACE-MAESTRO, Aura-MLS, HIRDLS, SMILES, and OMPS-LP. It describes the Data Initiative's top-down climatological validation approach to compare stratospheric composition measurements based on zonal monthly mean fields, which provides upper bounds to relative inter-instrument biases and an assessment of how well the instruments are able to capture geophysical features of the stratosphere. An update to previously published evaluations of O3 and H2O monthly mean time series is provided. In addition, example trace gas evaluations of methane (CH4), carbon monoxide (CO), a set of nitrogen species (NO, NO2, and HNO3), the reactive nitrogen family (NOy), and hydroperoxyl (HO2) are presented. The results highlight the quality, strengths and weaknesses, and representativeness of the different datasets. As a summary, the current state of our knowledge of stratospheric composition and variability is provided based on the overall consistency between the datasets. As such, the SPARC Data Initiative datasets and evaluations can serve as an atlas or reference of stratospheric composition and variability during the “golden age” of atmospheric limb sounding. The updated SPARC Data Initiative zonal monthly mean time series for each instrument are publicly available and accessible via the Zenodo data archive (Hegglin et al., 2020).

Stratospheric water vapor and ozone response to different QBO disruption events in 2016 and 2020

“…The version 4.4 MLS data set used here has a vertical resolution of 2.5-3 km ranging from 8 to 35 km and 60 • S/N with a high precision and lower systematic uncertainty (Santee et al, 2017). Previous findings show that MLS zonal monthly mean H 2 O mixing ratios show very good agreement with the multi-instrument mean (Hegglin et al, 2013(Hegglin et al, , 2021.…”

Methane's Solar Radiative Forcing

“…(2017), and Hegglin et al. (2021), respectively. Datasets containing principal results (monthly means) are available at the University of Reading Research Data Archive via https://doi.org/10.17864/1947.000396 (Byrom & Shine, 2022).…”

“…CH 4 mole fractions are derived from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) climatology (Hegglin et al, 2021), comprising zonal-mean values averaged between 2005 and 2012 from 300 hPa to 0.1 hPa at a 5° spatial resolution. Text S2 in Supporting Information S1 describes this dataset further and details how these fields are utilized to construct pre-industrial CH 4 mole fraction profiles.…”

“…The SOCRATES radiative transfer code and documentation is available from https://code.metoffice.gov.uk/trac/ socrates under an open source license but requires a free account from the UK Met Office (Scientific_Partnerships@metoffice.gov.uk) to access the website. ERA-interim renalysis, SCIAMACHY LER and MIPAS CH 4 climatology data are available via the in-text references Dee et al (2011), Tilstra et al (2017), and Hegglin et al (2021, respectively. Datasets containing principal results (monthly means) are available at the University of Reading Research Data Archive via https://doi.org/10.17864/1947.000396 .…”

Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results

“…The MIPAS HOCl measurements were taken at about 10:00 and 22: Good agreement was obtained, overall, versus the expected HOCl diurnal variations, despite the noise in some of the data sets (with SMILES HOCl producing the least noisy data). In SPARC (2017), HOCl monthly zonal mean distributions from MIPAS, SMILES, and MLS were intercompared, albeit not for the same range of years (see also the recent update by Hegglin et al, 2021). Nighttime values were used, as this time period exhibits somewhat smaller changes versus local time than the daytime data.…”