The Global Space-based Stratospheric Aerosol Climatology (version 2.0): 1979–2018

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).

OMPS LP Version 2.0 multi-wavelength aerosol extinction coefficient retrieval algorithm

“…Carbonyl sulfide (OCS) makes the second largest contribution to the aerosol layer. These sulfur species originate at the Earth's surface in a variety of reduced forms (including CS 2 , DMS and H 2 S) before oxidation in the atmosphere (Kremser et al, 2016). Other sources of stratospheric aerosol include the transport of tropospheric aerosol across the tropical tropopause through large convective systems such as the Asian monsoon (Vernier et al, 2011a;Thomason and Vernier, 2013).…”

“…Over the past few years, there has been a rising interest in the geoengineering concept for solar radiation management, by injecting aerosol into the stratosphere (Rasch et al, 2008), for which a basic understanding of the present stratospheric aerosol layer is essential. A review paper by Kremser et al (2016) concluded that it is critical to maintain continuous observational records to detect unpredictable events (like large volcanic eruptions) or unexpected developments (such as non-volcanic processes like strong PyroCb events that result in changes in stratospheric aerosol levels), noting that observations are critical for testing the reliability of climate models.…”

“…The V1 Level-3 CALIPSO stratospheric aerosol profile product was produced using only the nighttime measurements, and substantial spatial (vertical averaging to 900 m, 5 • latitude bins, 20 • longitude bins) and temporal (monthly) averaging were applied. A constant lidar ratio (extinction-to-backscatter ratio) of 50 sr was used to obtain the extinction profiles, which is a typical value used for stratospheric aerosol background conditions (Kremser et al, 2016). The extinction profiles were retrieved using two different methods.…”

“…CALIPSO 532 nm extinction (allaerosol mode) is converted to 745 nm using an Ångström exponent of 1.9, similar to the Ångström exponent for the OMPS assumed aerosol model. We also included SAGE III/ISS measurements at 755 nm as an independent reference, since SAGE measurements are widely considered to be the most accurate stratospheric aerosol dataset (SPARC, 2006;von Savigny et al, 2015;Kremser et al, 2016;Thomason et al, 2018;Kar et al, 2019). Although coverage and sampling differences can make such comparisons difficult, it provides a chance to evaluate the entire OMPS LP data record relative to these two datasets.…”

Evidence for the predictability of changes in the stratospheric aerosol size following volcanic eruptions of diverse magnitudes using space-based instruments

“…In addition, as sulfuric acid aerosol particles absorb upwelling infrared radiation, the presence of a volcanic aerosol layer can change the thermal structure of the stratosphere (Labitzke, 1994) and the troposphere and modulate stratospheric circulation as well as transport across the tropopause (Pitari et al, 2016). Significant effort has been expended toward measuring stratospheric aerosol using a variety of instruments (Kremser et al, 2016), and an extensive data collection of observations are now available. Some global climate models (GCMs) and Earth system models (ESMs) use these measurements or parameters directly derived from them (Mann et al, 2015), whereas others, which L. W. Thomason et al: Evidence for the predictability of changes in the stratospheric aerosol size use interactive aerosol model schemes (Mills et al, 2016) and similar tools (Toohey et al, 2016), assess how well their tools replicate observations and, thus, infer the reliability of the models' assessment of the climate impact of volcanic eruptions (Timmreck et al, 2016).…”