Abstract
Abstract. Artificial injections of sulfur dioxide (SO2) into the stratosphere show in several model studies an impact on stratospheric dynamics. The quasi-biennial oscillation (QBO) has been shown to slow down or even vanish under higher SO2 injections in the equatorial region. But the impact is only qualitatively but not quantitatively consistent across the different studies using different numerical models. The aim of this study is to understand the reasons behind the differences in the QBO response to SO2 injections between two general circulation models, the Whole Atmosphere Community Climate Model (WACCM-110L) and MAECHAM5-HAM. We show that the response of the QBO to injections with the same SO2 injection rate is very different in the two models, but similar when a similar stratospheric heating rate is induced by SO2 injections of different amounts. The reason for the different response of the QBO corresponding to the same injection rate is very different vertical advection in the two models, even in the control simulation. The stronger vertical advection in WACCM results in a higher aerosol burden and stronger heating of the aerosols and, consequently, in a vanishing QBO at lower injection rate than in simulations with MAECHAM5-HAM. The vertical velocity increases slightly in MAECHAM5-HAM when increasing the horizontal resolution. This study highlights the crucial role of dynamical processes and helps to understand the large uncertainties in the response of different models to artificial SO2 injections in climate engineering studies.
Highlights
Recent model intercomparison studies of sulfate evolution and transport after volcanic eruptions and after artificial injections of SO2 into the stratosphere reveal substantial differences between model results
We show that the response of the quasi-biennial oscillation (QBO) to injections with the same SO2 injection rate is very different in the two models, but similar when a similar stratospheric heating rate is induced by SO2 injections of different amounts
We performed here simulations with different injection rates of SO2 at the Equator to compare the impact on the QBO in two different general circulation models (WACCM and ECHAM)
Summary
Recent model intercomparison studies of sulfate evolution and transport after volcanic eruptions and after artificial injections of SO2 into the stratosphere reveal substantial differences between model results. The lifetime of the aerosols after a simulated Tambora-like eruption differs by several months and the aerosol optical depth (AOD) shows different maximum values and decay rates (Zanchettin et al, 2016; Marshall et al, 2018). Similar differences in response are found in climate engineering (CE) studies, in which SO2 is continuously injected into the stratosphere over a period of many years. Niemeier and Tilmes (2017) show a wide range of radiative forcing values resulting from the same sulfur injection rate but in different models. Radiative forcing results of the two models compared in Kleinschmitt et al (2017) are closer but still vary by 0.5 W m−2 for an injection rate of 10 Tg(S) yr−1. Kleinschmitt et al (2017) assumed differences in aerosol heating and consequent stronger vertical advection as a reason for the differences
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