scholarly journals Size-Resolved Stratospheric Aerosol Distributions after Pinatubo Derived from a Coupled Aerosol-Chemistry-Climate Model

2018 ◽  
Author(s):  
Timofei Sukhodolov ◽  
Jian-Xiong Sheng ◽  
Aryeh Feinberg ◽  
Bei-Ping Luo ◽  
Thomas Peter ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Climate Model ◽  
Reference Model ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Aerosol Chemistry ◽  
Quasi Biennial Oscillation ◽  
Aerosol Parameters

Abstract. We evaluate how the coupled aerosol-chemistry-climate model SOCOL-AER represents the influence of the 1991 eruption of Mt. Pinatubo on stratospheric aerosol loading, aerosol microphysical processes, radiative effects, and atmospheric chemistry. The aerosol module includes comprehensive sulfur chemistry and microphysics, in which the particle size distribution is represented by 40 size bins spanning radii from 0.39 nm to 3.2 μm. Radiative forcing is computed online using aerosol optical properties calculated according to Mie theory. SOCOL-AER simulations are compared with satellite and in situ measurements of aerosol parameters, temperature reanalyses, and ozone observations. In addition to the reference model configuration, we performed a series of sensitivity experiments looking at different processes affecting the aerosol layer. An accurate sedimentation scheme is found to be essential to prevent particles diffusing too rapidly to high and low altitudes. The aerosol radiative feedback and the use of a nudged quasi-biennial oscillation help to keep aerosol in the tropics and significantly affect the evolution of the stratospheric aerosol burden, which improves the agreement with observed aerosol mass distributions. Changes in the aerosol distribution affected by an inclusion of Van der Waals forces to the particle coagulation scheme suggest improvements in particle effective radius, although other parameters (such as aerosol longevity) deteriorate. Modification of the Pinatubo emission rate also improves some aerosol parameters, while worsens others compared to observations. Observations themselves are highly uncertain and render it difficult to conclusively judge the necessity of further model reconfiguration. In conclusion, our results show that SOCOL-AER is capable of predicting the most important global-scale atmospheric and climate effects following volcanic eruptions, which is also a prerequisite for improved understanding of anthropogenic effects from sulfur emissions.

scholarly journals Stratospheric aerosol evolution after Pinatubo simulated with a coupled size-resolved aerosol–chemistry–climate model, SOCOL-AERv1.0

2018 ◽  
Vol 11 (7) ◽  
pp. 2633-2647 ◽  
Author(s):  
Timofei Sukhodolov ◽  
Jian-Xiong Sheng ◽  
Aryeh Feinberg ◽  
Bei-Ping Luo ◽  
Thomas Peter ◽  
...  
Keyword(s):  
Climate Model ◽  
Reference Model ◽  
Volcanic Eruptions ◽  
Global Scale ◽  
Stratospheric Aerosol ◽  
Atmospheric Effects ◽  
Aerosol Layer ◽  
Aerosol Chemistry ◽  
Quasi Biennial Oscillation ◽  
Aerosol Parameters

Abstract. We evaluate how the coupled aerosol–chemistry–climate model SOCOL-AERv1.0 represents the influence of the 1991 eruption of Mt. Pinatubo on stratospheric aerosol properties and atmospheric state. The aerosol module is coupled to the radiative and chemical modules and includes comprehensive sulfur chemistry and microphysics, in which the particle size distribution is represented by 40 size bins with radii spanning from 0.39 nm to 3.2 µm. SOCOL-AER simulations are compared with satellite and in situ measurements of aerosol parameters, temperature reanalyses, and ozone observations. In addition to the reference model configuration, we performed series of sensitivity experiments looking at different processes affecting the aerosol layer. An accurate sedimentation scheme is found to be essential to prevent particles from diffusing too rapidly to high and low altitudes. The aerosol radiative feedback and the use of a nudged quasi-biennial oscillation help to keep aerosol in the tropics and significantly affect the evolution of the stratospheric aerosol burden, which improves the agreement with observed aerosol mass distributions. The inclusion of van der Waals forces in the particle coagulation scheme suggests improvements in particle effective radius, although other parameters (such as aerosol longevity) deteriorate. Modification of the Pinatubo sulfur emission rate also improves some aerosol parameters, while it worsens others compared to observations. Observations themselves are highly uncertain and render it difficult to conclusively judge the necessity of further model reconfiguration. The model revealed problems in reproducing aerosol sizes above 25 km and also in capturing certain features of the ozone response. Besides this, our results show that SOCOL-AER is capable of predicting the most important global-scale atmospheric effects following volcanic eruptions, which is also a prerequisite for an improved understanding of solar geoengineering effects from sulfur injections to the stratosphere.

scholarly journals Sensitivity of the radiative forcing by stratospheric sulfur geoengineering to the amount and strategy of the SO<sub>2</sub>injection studied with the LMDZ-S3A model

2018 ◽  
Vol 18 (4) ◽  
pp. 2769-2786 ◽  
Author(s):  
Christoph Kleinschmitt ◽  
Olivier Boucher ◽  
Ulrich Platt
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Quasi Biennial Oscillation ◽  
Detailed Model ◽  
Mass Unit ◽  
Modelling Studies ◽  
Injection Rates

Abstract. The enhancement of the stratospheric sulfate aerosol layer has been proposed as a method of geoengineering to abate global warming. Previous modelling studies found that stratospheric aerosol geoengineering (SAG) could effectively compensate for the warming by greenhouse gases on the global scale, but also that the achievable cooling effect per sulfur mass unit, i.e. the forcing efficiency, decreases with increasing injection rate. In this study we use the atmospheric general circulation model LMDZ with the sectional aerosol module S3A to determine how the forcing efficiency depends on the injected amount of SO2, the injection height, and the spatio-temporal pattern of injection. We find that the forcing efficiency may decrease more drastically for larger SO2 injections than previously estimated. As a result, the net instantaneous radiative forcing does not exceed the limit of –2 W m−2 for continuous equatorial SO2 injections and it decreases (in absolute value) for injection rates larger than 20 Tg S yr−1. In contrast to other studies, the net radiative forcing in our experiments is fairly constant with injection height (in a range 17 to 23 km) for a given amount of SO2 injected. Also, spreading the SO2 injections between 30∘ S and 30∘ N or injecting only seasonally from varying latitudes does not result in a significantly larger (i.e. more negative) radiative forcing. Other key characteristics of our simulations include a consequent stratospheric heating, caused by the absorption of solar and infrared radiation by the aerosol, and changes in stratospheric dynamics, with a collapse of the quasi-biennial oscillation at larger injection rates, which has impacts on the resulting spatial aerosol distribution, size, and optical properties. But it has to be noted that the complexity and uncertainty of stratospheric processes cause considerable disagreement among different modelling studies of stratospheric aerosol geoengineering. This may be addressed through detailed model intercomparison activities, as observations to constrain the simulations of stratospheric aerosol geoengineering are not available and analogues (such as volcanic eruptions) are imperfect.

scholarly journals The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): Experimental design and forcing input data

2016 ◽  
Author(s):  
Davide Zanchettin ◽  
Myriam Khodri ◽  
Claudia Timmreck ◽  
Matthew Toohey ◽  
Anja Schmidt ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Initial Conditions ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Model Intercomparison ◽  
Climatic Response ◽  
Volcanic Forcing ◽  
Intercomparison Project

Abstract. The enhancement of the stratospheric aerosol layer by volcanic eruptions induces a complex set of responses causing global and regional climate effects on a broad range of timescales. Uncertainties exist regarding the climatic response to strong volcanic forcing identified in coupled climate simulations that contributed to the fifth phase of the Climate Model Intercomparison Project (CMIP5). In order to better understand the sources of these model diversities, the model intercomparison project on the climate response to volcanic forcing (VolMIP) has defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the CMIP6 protocol. VolMIP provides a common stratospheric aerosol dataset for each experiment to eliminate differences in the applied volcanic forcing, and defines a set of initial conditions to determine how internal climate variability contributes to determining the response. VolMIP will assess to what extent volcanically-forced responses of the coupled ocean-atmosphere system are robustly simulated by state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in the treatment of physical processes. This paper illustrates the design of the idealized volcanic perturbation experiments in the VolMIP protocol and describes the common aerosol forcing input datasets to be used.

scholarly journals Particulate sulfur in the upper troposphere and lowermost stratosphere – sources and climate forcing

2017 ◽  
Vol 17 (18) ◽  
pp. 10937-10953 ◽  
Author(s):  
Bengt G. Martinsson ◽  
Johan Friberg ◽  
Oscar S. Sandvik ◽  
Markus Hermann ◽  
Peter F. J. van Velthoven ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Radiative Forcing ◽  
Chemical Elements ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Pixe Analysis ◽  
Upper Troposphere ◽  
Particulate Sulfur ◽  
Fine Mode

Abstract. This study is based on fine-mode aerosol samples collected in the upper troposphere (UT) and the lowermost stratosphere (LMS) of the Northern Hemisphere extratropics during monthly intercontinental flights at 8.8–12 km altitude of the IAGOS-CARIBIC platform in the time period 1999–2014. The samples were analyzed for a large number of chemical elements using the accelerator-based methods PIXE (particle-induced X-ray emission) and PESA (particle elastic scattering analysis). Here the particulate sulfur concentrations, obtained by PIXE analysis, are investigated. In addition, the satellite-borne lidar aboard CALIPSO is used to study the stratospheric aerosol load. A steep gradient in particulate sulfur concentration extends several kilometers into the LMS, as a result of increasing dilution towards the tropopause of stratospheric, particulate sulfur-rich air. The stratospheric air is diluted with tropospheric air, forming the extratropical transition layer (ExTL). Observed concentrations are related to the distance to the dynamical tropopause. A linear regression methodology handled seasonal variation and impact from volcanism. This was used to convert each data point into stand-alone estimates of a concentration profile and column concentration of particulate sulfur in a 3 km altitude band above the tropopause. We find distinct responses to volcanic eruptions, and that this layer in the LMS has a significant contribution to the stratospheric aerosol optical depth and thus to its radiative forcing. Further, the origin of UT particulate sulfur shows strong seasonal variation. We find that tropospheric sources dominate during the fall as a result of downward transport of the Asian tropopause aerosol layer (ATAL) formed in the Asian monsoon, whereas transport down from the Junge layer is the main source of UT particulate sulfur in the first half of the year. In this latter part of the year, the stratosphere is the clearly dominating source of particulate sulfur in the UT during times of volcanic influence and under background conditions.

scholarly journals Exploring accumulation-mode H<sub>2</sub>SO<sub>4</sub> versus SO<sub>2</sub> stratospheric sulfate geoengineering in a sectional aerosol–chemistry–climate model

2019 ◽  
Vol 19 (7) ◽  
pp. 4877-4897 ◽  
Author(s):  
Sandro Vattioni ◽  
Debra Weisenstein ◽  
David Keith ◽  
Aryeh Feinberg ◽  
Thomas Peter ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Continuous Production ◽  
Stratospheric Aerosol ◽  
So2 Emissions ◽  
Aerosol Chemistry ◽  
Accumulation Mode ◽  
Direct Emission ◽  
Equivalent Mass ◽  
The Tropics

Abstract. Stratospheric sulfate geoengineering (SSG) could contribute to avoiding some of the adverse impacts of climate change. We used the SOCOL-AER global aerosol–chemistry–climate model to investigate 21 different SSG scenarios, each with 1.83 Mt S yr−1 injected either in the form of accumulation-mode H2SO4 droplets (AM H2SO4), gas-phase SO2 or as combinations of both. For most scenarios, the sulfur was continuously emitted at an altitude of 50 hPa (≈20 km) in the tropics and subtropics. We assumed emissions to be zonally and latitudinally symmetric around the Equator. The spread of emissions ranged from 3.75∘ S–3.75∘ N to 30∘ S–30∘ N. In the SO2 emission scenarios, continuous production of tiny nucleation-mode particles results in increased coagulation, which together with gaseous H2SO4 condensation, produces coarse-mode particles. These large particles are less effective for backscattering solar radiation and have a shorter stratospheric residence time than AM H2SO4 particles. On average, the stratospheric aerosol burden and corresponding all-sky shortwave radiative forcing for the AM H2SO4 scenarios are about 37 % larger than for the SO2 scenarios. The simulated stratospheric aerosol burdens show a weak dependence on the latitudinal spread of emissions. Emitting at 30∘ N–30∘ S instead of 10∘ N–10∘ S only decreases stratospheric burdens by about 10 %. This is because a decrease in coagulation and the resulting smaller particle size is roughly balanced by faster removal through stratosphere-to-troposphere transport via tropopause folds. Increasing the injection altitude is also ineffective, although it generates a larger stratospheric burden, because enhanced condensation and/or coagulation leads to larger particles, which are less effective scatterers. In the case of gaseous SO2 emissions, limiting the sulfur injections spatially and temporally in the form of point and pulsed emissions reduces the total global annual nucleation, leading to less coagulation and thus smaller particles with increased stratospheric residence times. Pulse or point emissions of AM H2SO4 have the opposite effect: they decrease the stratospheric aerosol burden by increasing coagulation and only slightly decrease clear-sky radiative forcing. This study shows that direct emission of AM H2SO4 results in higher radiative forcing for the same sulfur equivalent mass injection strength than SO2 emissions, and that the sensitivity to different injection strategies varies for different forms of injected sulfur.

scholarly journals The Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP): motivation and experimental design

2018 ◽  
Vol 11 (7) ◽  
pp. 2581-2608 ◽  
Author(s):  
Claudia Timmreck ◽  
Graham W. Mann ◽  
Valentina Aquila ◽  
Rene Hommel ◽  
Lindsay A. Lee ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Transport Processes ◽  
Aerosol Layer ◽  
Model Intercomparison ◽  
Aerosol Model ◽  
Model Experiments ◽  
Aerosol Forcing ◽  
Intercomparison Project

Abstract. The Stratospheric Sulfur and its Role in Climate (SSiRC) Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP) explores uncertainties in the processes that connect volcanic emission of sulfur gas species and the radiative forcing associated with the resulting enhancement of the stratospheric aerosol layer. The central aim of ISA-MIP is to constrain and improve interactive stratospheric aerosol models and reduce uncertainties in the stratospheric aerosol forcing by comparing results of standardized model experiments with a range of observations. In this paper we present four co-ordinated inter-model experiments designed to investigate key processes which influence the formation and temporal development of stratospheric aerosol in different time periods of the observational record. The Background (BG) experiment will focus on microphysics and transport processes under volcanically quiescent conditions, when the stratospheric aerosol is controlled by the transport of aerosols and their precursors from the troposphere to the stratosphere. The Transient Aerosol Record (TAR) experiment will explore the role of small- to moderate-magnitude volcanic eruptions, anthropogenic sulfur emissions, and transport processes over the period 1998–2012 and their role in the warming hiatus. Two further experiments will investigate the stratospheric sulfate aerosol evolution after major volcanic eruptions. The Historical Eruptions SO2 Emission Assessment (HErSEA) experiment will focus on the uncertainty in the initial emission of recent large-magnitude volcanic eruptions, while the Pinatubo Emulation in Multiple models (PoEMS) experiment will provide a comprehensive uncertainty analysis of the radiative forcing from the 1991 Mt Pinatubo eruption.

scholarly journals 35 years of stratospheric aerosol measurements at Garmisch-Partenkirchen: from Fuego to Eyjafjallajökull, and beyond

2012 ◽  
Vol 12 (9) ◽  
pp. 23135-23193 ◽  
Author(s):  
T. Trickl ◽  
H. Giehl ◽  
H. Jäger ◽  
H. Vogelmann
Keyword(s):  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Saharan Dust ◽  
Positive Trend ◽  
Aerosol Layer ◽  
Quasi Biennial Oscillation ◽  
Mauna Loa ◽  
Background Period ◽  
Lidar Measurements ◽  
Volcanic Impact

Abstract. The powerful backscatter lidar at Garmisch-Partenkirchen (Germany) has almost continually delivered backscatter coefficients of the stratospheric aerosol since 1976. The time series is dominated by signals from the particles injected into or formed in the stratosphere due to major volcanic eruptions, in particular those of El Chichon (Mexico, 1982) and Mt. Pinatubo (Philippines, 1991). The volcanic aerosol disappears within about five years, the removal from the stratosphere being modulated by the phase of the quasi-biennial oscillation. Here, we focus more on the long-lasting background period since the late 1990s and 2006, in view of processes maintaining a residual lower-stratospheric aerosol layer in absence of major eruptions, as well as the period of moderate volcanic impact afterwards. During the long background period the stratospheric backscatter coefficients reached a level even below that observed in the late 1970s. This suggests that the predicted potential influence of the strongly growing air traffic on the stratospheric aerosol loading is very low. Some correlation may be found with single strong forest-fire events, but the average influence of biomass burning seems to be quite limited. No positive trend in background aerosol can be resolved over a period as long as that observed by lidar at Mauna Loa or Boulder. This suggests being careful with invoking Asian air pollution as the main source as found in the literature. Rather an impact of previously missed volcanic eruptions on the stratospheric aerosol must be taken into consideration. A key observation in this regard was that of the plume from the Icelandic volcano Eyjafjallajökull above Garmisch-Partenkirchen (April 2010) due to the proximity of that source. The top altitude of the ash next to the source was reported just as roughly 9.3 km, but the lidar measurements revealed enhanced stratospheric aerosol up to 14.5 km. Our analysis suggests for two, perhaps three, of the four measurement days the presence of a stratospheric contribution from Iceland related to quasi-horizontal transport, contrasting the strongly descending lower layers entering Central Europe. The backscatter coefficients within the first 2 km above the tropopause exceed the stratospheric background by a factor of three to four. In addition, Asian and Saharan dust layers were identified in the free troposphere, Asian dust most likely even in the stratosphere. The number of minor mid-latitude eruptions has gradually increased during the past ten years. We conclude that, although their stratospheric contribution could not be clearly identified above our site they can sum up for forming some minor background. Clear stratospheric signatures were only seen in the case of eruptions reaching higher altitudes.

Volcanic forcing of climate since 1850 in an interactive aerosol-chemistry-climate model

2021 ◽  
Author(s):  
Thomas Aubry ◽  
Anja Schmidt ◽  
Alix Harrow ◽  
Jeremy Walton ◽  
Jane Mulcahy ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Coupled Model ◽  
Ice Cores ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Model ◽  
Volcanic Forcing

&lt;p&gt;Reconstructions of volcanic aerosol forcing and its climatic impacts are undermined by uncertainties in both the models used to build these reconstructions as well as the proxy and observational records used to constrain those models. Reducing these uncertainties has been a priority and in particular, several modelling groups have developed interactive stratospheric aerosol models. Provided with an initial volcanic injection of sulfur dioxide, these models can interactively simulate the life cycle and optical properties of sulfate aerosols, and their effects on climate. In contrast, most climate models that took part in the Coupled Model Intercomparison Project Phase 5 and 6 (CMIP6) directly prescribe perturbations in atmospheric optical properties associated with an eruption. However, before the satellite era, the volcanic forcing dataset used for CMIP6 mostly relies on a relatively simple aerosol model and a volcanic sulfur inventory derived from ice-cores, both of which have substantial associated uncertainties.&lt;/p&gt;&lt;p&gt;In this study, we produced a new set of historical simulations using the UK Earth System Model UKESM1, with interactive stratospheric aerosol capability (referred to as interactive runs hereafter) instead of directly prescribing the CMIP6 volcanic forcing dataset as was done for CMIP6 (standard runs, hereafter). We used one of the most recent volcanic sulfur inventories as input for the interactive runs, in which aerosol properties are consistent with the model chemistry, microphysics and atmospheric components. We analyzed how the stratospheric aerosol optical depth, the radiative forcing and the climate response to volcanic eruptions differed between interactive and standard runs, and how these compare to observations and proxy records. In particular, we investigate in detail the differences in the response to the large-magnitude Krakatoa 1883 eruption between the two sets of runs. We also discuss differences for the 1979-2015 period where the forcing data in standard runs is directly constrained from satellite observations. Our results shed new light on uncertainties affecting the reconstruction of past volcanic forcing and highlight some of the benefits and disadvantages of using interactive stratospheric aerosol capabilities instead of a unique prescribed volcanic forcing dataset in CMIP&amp;#8217;s historical runs.&lt;/p&gt;

scholarly journals Exploring accumulation-mode-H<sub>2</sub>SO<sub>4</sub> versus SO<sub>2</sub> stratospheric sulfate geoengineering in a sectional aerosol-chemistry-climate model

2018 ◽  
Author(s):  
Sandro Vattioni ◽  
Debra Weisenstein ◽  
David Keith ◽  
Aryeh Feinberg ◽  
Thomas Peter ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Surf Zone ◽  
Climate Model ◽  
Continuous Production ◽  
Short Wave ◽  
Stratospheric Aerosol ◽  
Aerosol Chemistry ◽  
Accumulation Mode ◽  
So2 Flux ◽  
Direct Emission

Abstract. Stratospheric sulfate geoengineering (SSG) could contribute to avoiding some of the adverse impacts of climate change. We used the global 3D-aerosol-chemistry-climate model, SOCOL-AER, to investigate 21 different SSG scenarios, each with 1.83 Mt S yr−1 injected either in the form of accumulation-mode-H2SO4 droplets (AM-H2SO4), gas-phase SO2, or as combinations of both. For most scenarios, the sulfur was continuously emitted at 50 hPa (≈ 20 km) altitude in the tropics and subtropics, zonally and latitudinally symmetric about the equator (ranging from &amp;pm;3.75° to &amp;pm;30°). In the SO2 emission scenarios, continuous production of tiny nucleation mode particles results in increased coagulation, which together with condensation produces larger coarse mode particles. These larger particles are less effective for backscattering solar radiation and sedimentation out of the stratosphere is faster. On average, AM-H2SO4 injection increases stratospheric aerosol residence times by 32 % and stratospheric aerosol burdens 37–41 % when comparing to SO2 injection. The modelled all-sky (clear-sky) short-wave radiative forcing for AM-H2SO4 injection scenarios is up to 17–70 % (44 %–57 %) larger than is the case for SO2. Aerosol burdens have a surprisingly week dependence on the latitudinal spread of emissions with emission in the stratospheric surf zone (> 15° N–15° S) decreasing burdens by only about 10 %. This is because the faster removal through stratosphere-to-troposphere transport via tropopause folds found when injection is spread farther from the equator is roughly balanced by a decrease in coagulation. Increasing injection altitude is also surprisingly ineffective because the increase in burden is compensated by an increase in large aerosols due to increased condensation. Increasing the local SO2 flux in the injection region by pulse or point emissions reduces the total global annual nucleation. Coagulation is also reduced due to the interruption of the continuous flow of freshly formed particles. The net effect of pulse or point emission of SO2 is to increase stratospheric aerosol residence time and radiative forcing. Pulse or point emissions of AM-H2SO4 has the opposite effect—decreasing stratospheric aerosol burden and radiative forcing by increasing coagulation. In summary, this study corroborates previous studies with uncoupled aerosol and radiation modules, suggesting that, compared to SO2 injection, the direct emission of AM-H2SO4 results in more radiative forcing for the same sulfur equivalent mass injection strength and that sensitivities to different injection strategies may vary for different forms of injected sulfur.

scholarly journals Stratospheric SO<sub>2</sub> and sulphate aerosol, model simulations and satellite observations

2013 ◽  
Vol 13 (4) ◽  
pp. 11395-11425 ◽  
Author(s):  
C. Brühl ◽  
J. Lelieveld ◽  
M. Höpfner ◽  
H. Tost
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Lower Boundary ◽  
Circulation Model ◽  
Volcanic Eruptions ◽  
Satellite Observations ◽  
Quasi Biennial Oscillation ◽  
Tropospheric Aerosol

Abstract. A multiyear study with the atmospheric chemistry general circulation model EMAC with the aerosol module GMXe at high altitude resolution demonstrates that the sulfur gases COS and SO2, the latter from low-latitude volcanic eruptions, predominantly control the formation of stratospheric aerosol. The model consistently uses the same parameters in the troposphere and stratosphere for 7 aerosol modes applied. Lower boundary conditions for COS and other long-lived trace gases are taken from measurement networks, while estimates of volcanic SO2 emissions are based on satellite observations. We show comparisons with satellite data for aerosol extinction (e.g. SAGE) and SO2 in the middle atmosphere (MIPAS on ENVISAT). This corroborates the interannual variability induced by the Quasi-Biennial Oscillation, which is internally generated by the model. The model also realistically simulates the radiative effects of stratospheric and tropospheric aerosol including the effects on the model dynamics. The medium strength volcanic eruptions of 2005 and 2006 exerted a nonnegligible radiative forcing of up to −0.6 W m−2 in the tropics, while the large Pinatubo eruption caused a maximum though short term tropical forcing of about −10 W m−2. The study also shows that observed upper stratospheric SO2 can be simulated accurately only when a sulphur sink on meteoritic dust is included and the photolysis of gaseous H2SO4 in the near infrared is higher than assumed previously.

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