Impacts of Mt. Pinatubo volcanic aerosol on the tropical stratosphere in chemistry-climate model simulations using CCMI and CMIP6 stratospheric aerosol data.

Abstract:

For phase 6 of the Coupled Model Intercomparison Project (CMIP6) and the Chemistry-Climate Model Initiative (CCMI), two stratospheric aerosol data sets were compiled for use by chemistry-climate models that do not include an online aerosol module. The data sets provide temporally and spatially resolved aerosol size parameters for heterogeneous chemistry and aerosol radiative properties as a function of wavelength. The “SAGE-4λ” data set was compiled for CCMI, and the “SAGE-3λ” data set was compiled for CMIP6. These data sets are both based on SAGE (Stratospheric Aerosol and Gas Experiment) II satellite measurements. Following the Mt. Pinatubo eruption in 1991, when the stratosphere was too optically opaque for SAGE II, the SAGE-4λ data set was gap-filled with ground-based Lidar measurements, while the SAGE-3λ data set was gap-filled using measurements from CLAES (Cryogenic Limb Array Etalon Spectrometer) on UARS, the Upper Atmosphere Research Satellite. We performed SOCOLv3 (Solar Climate Ozone Links version 3) chemistry-climate model simulations of the recent past (1986–2005) to investigate the impact of the Mt. Pinatubo eruption in 1991 on stratospheric temperature and ozone and how this response differs depending on which aerosol data set is applied.

In the simulations using SAGE-4λ aerosols, heating and ozone loss are overestimated in the post-eruption period in the tropical lower stratosphere compared to observations, by approximately 3 K and 0.2 ppmv, respectively. The different gap-filling procedure used for the SAGE-3λ data set in the post-Pinatubo eruption period means that less heating occurs in the model simulations using SAGE-3λ stratospheric aerosols. Tropical temperature anomalies in these simulations are in good agreement with MERRA and ERA-Interim reanalyses in the post-eruption period. Differences in the rate of tropical upwelling and of ozone destruction chemistry by the odd nitrogen and chlorine cycles means that, in the SAGE-3λ simulations, ozone is in better agreement with observations from the SWOOSH record than in the simulations based on SAGE-4λ. Overall, the CMIP6 stratospheric aerosol data set, SAGE-3λ, allows SOCOLv3 to more accurately simulate tropical stratospheric temperature and ozone during the post-Pinatubo eruption period.