Analyzing composition and trends of the Asian Tropopause Aerosol Layer
Final Report Abstract
Chemistry, dynamics and microphysics of the stratosphere and the tropopause region play a crucial role for the climate system. Trace gases and aerosol in the stratosphere have a longer lifetime compared to lower altitudes, which increases their impact on the climate. One important component for the climate system is stratospheric aerosol. By backscattering shortwave radiation to space, stratospheric aerosol has a significant cooling effect on the climate. Aerosols are either directly injected into the Upper Troposphere and Lower Stratosphere (UTLS) during moderate/major volcanic eruptions and extreme wildfire events or converted from aerosol precursors (e.g. Carbonyl sulfide). One important pathway for aerosols and aerosol precursors from the ground into the UTLS is the Asian monsoon. Air masses are lifted and confined within the boundaries of the Asian monsoon anticyclone (AMA). During the DFG project (at CNRS, LPC2E, France) I observed enhanced aerosols within the Asian monsoon anticyclone (AMA) with a new space-borne data sets SAGE III/ISS, confirming the first detection of the Asian Tropopause Aerosol Layer (ATAL) with the satellite instrument CALIOP. I furthermore investigated the evolution of the ATAL during and prior to the 1990 with old satellite observations (SAGE I and II) and found, other than previously assumed, that the ATAL has been present and detectable throughout the whole data record underlying a year to year variability due to limited profile averaging and the natural variability of the ATAL itself. A major volcanic eruption significantly changes the aerosol content in the stratosphere with a direct climate impact, resulting in a significant temperature decrease on the Earth’s surface. Moderate but more recurrent volcanic eruptions on the aerosol layer and the radiative balance were shown to have a significant impact. Furthermore, as a new phenomenon, recent extreme wildfire events had a comparable impact on the stratospheric aerosol to moderate volcanic eruptions. Those events are even expected to increase in extent and frequency with global warming. During my DFG project, I studied the global impact of the most recent stratospheric aerosol events: The Canadian fires 2017, volcanic eruptions at Ambae 2018 and Raikoke/Ulawun 2019, Australian fires 2020. We show that the circulation of the AMA played an important role in transporting plume air masses from UTLS northern latitudes to the tropics. The eruption at Ambae was mostly overlooked in the literature. We show that two significant stratospheric injections took place, with a perturbation of the global stratospheric aerosol throughout one year, with stratospheric aerosol depth peak values at 0.01. The more complex situation around the Raikoke eruption is first described in Kloss et al. (2021). It had mostly an impact on the northern hemisphere, with AOD values up to 0.025. Differences between model simulations and satellite observations let us suspect that ash might have played a significant role for the distribution and lifetime of the Raikoke plume particles. We furthermore studied the long-range transport of dense CO and other trace gas plumes within the UTLS during the Australian fires 2019/2020 already in November, before the prominent pyro-Cb convection events during New Year 2019/2020.
Publications
- ‘Transport of the 2017 Canadian wildfire plume to the tropics and global stratosphere via the Asian monsoon circulation ‘, Atmospheric Chemistry and Physics (2019)
Kloss C. et al.
(See online at https://doi.org/10.5194/acp-19-13547-2019) - ‘Impact of the 2018 Ambae eruption on the global stratospheric aerosol layer and climate’, Journal of Geophysical Research (2020)
Kloss C. et al.
(See online at https://doi.org/10.1029/2020JD032410) - ‘Global modelling studies of composition and decadal trends of the Asian Tropopause Aerosol Layer’, Atmospheric Chemistry and Physics Discussion (2021)
Bossolasco A. et al.
(See online at https://doi.org/10.5194/acp-21-2745-2021) - ‘Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions and climate impact’, Atmospheric Chemistry and Physics (2021)
Kloss et al.
(See online at https://doi.org/10.5194/acp-21-535-2021) - ‘Transport pathways in the Asian monsoon UTLS inferred from (StratoClim) trace gas observations’, Atmospheric Chemistry and Physics (2021)
Von Hobe M. et al.
(See online at https://doi.org/10.5194/acp-21-1267-2021)
