Abstract
Abstract. This paper presents decadal simulations of stratospheric and tropospheric aerosol and its radiative effects by the chemistry general circulation model EMAC constrained with satellite observations in the framework of the ESA Aerosol CCI project such as GOMOS (Global Ozone Monitoring by Occultation of Stars) and (A)ATSR ((Advanced) Along Track Scanning Radiometer) on the ENVISAT (European Environmental Satellite), IASI (Infrared Atmospheric Sounding Interferometer) on MetOp (Meteorological Operational Satellite), and, additionally, OSIRIS (Optical Spectrograph and InfraRed Imaging System). In contrast to most other studies, the extinctions and optical depths from the model are compared to the observations at the original wavelengths of the satellite instruments covering the range from the UV (ultraviolet) to terrestrial IR (infrared). This avoids conversion artifacts and provides additional constraints for model aerosol and interpretation of the observations. MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) SO2 limb measurements are used to identify plumes of more than 200 volcanic eruptions. These three-dimensional SO2 plumes are added to the model SO2 at the eruption times. The interannual variability in aerosol extinction in the lower stratosphere, and of stratospheric aerosol radiative forcing at the tropopause, is dominated by the volcanoes. To explain the seasonal cycle of the GOMOS and OSIRIS observations, desert dust simulated by a new approach and transported to the lowermost stratosphere by the Asian summer monsoon and tropical convection turns out to be essential. This also applies to the radiative heating by aerosol in the lowermost stratosphere. The existence of wet dust aerosol in the lowermost stratosphere is indicated by the patterns of the wavelength dependence of extinction in observations and simulations. Additional comparison with (A)ATSR total aerosol optical depth at different wavelengths and IASI dust optical depth demonstrates that the model is able to represent stratospheric as well as tropospheric aerosol consistently.
Highlights
Climate effects of stratospheric aerosols can be important, as analyzed for example by Solomon et al (2011), Santer et al (2014) and Ridley et al (2014)
We rely on the multiple instrument satellite dataset provided in the Climate Change Initiative (CCI) of the European Space Agency (ESA) (Popp et al, 2016), which was developed as a tool for evaluation and improvement of the treatment of stratospheric and tropospheric aerosols in global chemistry climate models, like the EMAC (ECHAM5/Modular Earth Submodel System (MESSy) Atmospheric Chemistry) model (Brühl et al, 2015)
The present paper is organized as follows: in Sect. 2, we briefly present the satellite datasets used to evaluate the model, and to check for consistency of observations at different wavelengths: GOMOS, IASI, (A)ATSR and OSIRIS
Summary
Climate effects of stratospheric aerosols can be important, as analyzed for example by Solomon et al (2011), Santer et al (2014) and Ridley et al (2014). That and the present study contribute to the SPARC/SSIRC initiative (Stratosphere-troposphere Processes And their Role in Climate / Stratospheric Sulfur and Its Role in Climate, see for example Timmreck et al, 2018), aiming at a better understanding of the composition, microphysical and radiative properties characteristics of stratospheric aerosols and their impact on climate (Kremser et al, 2016). We rely on the multiple instrument satellite dataset provided in the Climate Change Initiative (CCI) of the European Space Agency (ESA) (Popp et al, 2016), which was developed as a tool for evaluation and improvement of the treatment of stratospheric and tropospheric aerosols in global chemistry climate models, like the EMAC (ECHAM5/MESSy Atmospheric Chemistry) model (Brühl et al, 2015).
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