Abstract
Abstract. A robust stratospheric aerosol climate data record enables the depiction of the radiative forcing of this highly variable component of climate. In addition to the radiative forcing, stratospheric aerosol also plays a key role in the chemical processes leading to ozone depletion. Therefore, stratospheric aerosol is one of the crucial parameters in understanding climate change in the past and potential changes in the future. As a part of Stratospheric-tropospheric Processes and their Role in Climate (SPARC) Stratospheric Sulfur and its Role in Climate (SSiRC) activity, the Global Space-based Stratospheric Aerosol Climatology (GloSSAC) was created (Thomason et al., 2018) to support the World Climate Research Programme's (WCRP) Coupled Model Intercomparison Project Phase 6 (CMIP6) (Eyring et al., 2016). This data set is a follow-on to one created as a part of SPARC's Assessment of Stratospheric Aerosol Properties (ASAP) activity (SPARC, 2006) and a data created for the Chemistry-Climate Model Initiative (CCMI) in 2012 (Eyring and Lamarque, 2012). Herein, we discuss changes to the original release version including those as a part of v1.1 that was released in September 2018 that primarily corrects an error in the conversion of Cryogenic Limb Array Etalon Spectrometer (CLAES) data to Stratospheric Aerosol and Gas Experiment (SAGE) II wavelengths, as well as the new release, v2.0. Version 2.0 is focused on improving the post-SAGE II era (after 2005) with the goal of mitigating elevated aerosol extinction in the lower stratosphere at mid- and high latitudes noted in v1.0 as noted in Thomason et al. (2018). Changes include the use of version 7.0 of the Optical Spectrograph and InfraRed Imaging System (OSIRIS), the recently released Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar Level 3 stratospheric aerosol profile monthly product and the new addition of SAGE III/ISS. Here, we use an observed relationship between (i) OSIRIS extinction at 750 nm and (ii) SAGE II and SAGE III/ISS extinction at 525 nm to derive an altitude–latitude-based monthly climatology of Ångström exponent to compute OSIRIS extinction at 525 nm, resulting in a better agreement between OSIRIS and SAGE measurements. We employ a similar approach to convert OSIRIS 750 nm extinction to 1020 nm extinction for the post-SAGE II period. Additionally, we incorporate the recently released standard CALIPSO stratospheric aerosol profile monthly product into GloSSAC with an improved conversion technique of the 532 nm backscatter coefficient to extinction using an observed relationship between OSIRIS 525 nm extinction and CALIPSO 532 nm backscatter. SAGE III/ISS data are also incorporated in GloSSAC to extend the climatology to the present and to test the approach used to correct OSIRIS/CALIPSO data. The GloSSAC v2.0 netCDF file is accessible at https://doi.org/10.5067/glossac-l3-v2.0 (Thomason, 2020).
Highlights
Stratospheric aerosols play a key role in determining the chemical (e.g., Hofmann and Solomon, 1989; Fahey et al, 1993; Solomon et al, 1996) and radiative (e.g., Minnis et al, 1993; Ridley et al, 2014) balance of the atmosphere
For Global Space-based Stratospheric Aerosol Climatology (GloSSAC) v1.0, we used the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) version 4.0 level 1 aerosol data product at 532 nm and identified and removed observations that suggested the presence of cloud using the depolarization measurement
We present v2.0 of GloSSAC that extends from 1979 through 2018 with the addition of new Stratospheric Aerosol and Gas Experiment (SAGE) III/ISS data toward the end of the record and with some changes to the data used in the post-SAGE II era
Summary
Stratospheric aerosols play a key role in determining the chemical (e.g., Hofmann and Solomon, 1989; Fahey et al, 1993; Solomon et al, 1996) and radiative (e.g., Minnis et al, 1993; Ridley et al, 2014) balance of the atmosphere. An exception to this process was the higher-than-expected extinction in the lower stratosphere in mid- and high latitudes during the CALIOP/OSIRIS era based on observations at similar overall aerosol levels during the SAGE II period Both GloSSAC v1.0 and v1.1 retained these offsets in extinction as, at the time, it was not clear if the difference was due to real geophysical variability possibly driven by volcanic activity or due to deficiencies in conversion process or in the source data themselves. Very similar discrepancies were noted between OSIRIS and CALIOP data and SAGE III/ISS observations some 12 years later
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