Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

Abstract. Reduction of surface temperatures of the planet by injecting sulfate aerosols in the stratosphere has been suggested as an option to reduce the amount of human-induced climate warming. Several previous studies have shown that for a specified amount of injection, aerosols injected at a higher altitude in the stratosphere would produce more cooling because aerosol sedimentation would take longer. In this study, we isolate and assess the sensitivity of stratospheric aerosol radiative forcing and the resulting climate change to the altitude of the aerosol layer. We study this by prescribing a specified amount of sulfate aerosols, of a size typical of what is produced by volcanoes, distributed uniformly at different levels in the stratosphere. We find that stratospheric sulfate aerosols are more effective in cooling climate when they reside higher in the stratosphere. We explain this sensitivity in terms of effective radiative forcing: volcanic aerosols heat the stratospheric layers where they reside, altering stratospheric water vapor content, tropospheric stability, and clouds, and consequently the effective radiative forcing. We show that the magnitude of the effective radiative forcing is larger when aerosols are prescribed at higher altitudes and the differences in radiative forcing due to fast adjustment processes can account for a substantial part of the dependence of the amount of cooling on aerosol altitude. These altitude effects would be additional to dependences on aerosol microphysics, transport, and sedimentation, which are outside the scope of this study. The cooling effectiveness of stratospheric sulfate aerosols likely increases with the altitude of the aerosol layer both because aerosols higher in the stratosphere have larger effective radiative forcing and because they have higher stratospheric residence time; these two effects are likely to be of comparable importance.

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Climate System Response to Stratospheric Sulfate Aerosols: Sensitivity to Altitude of Aerosol Layer

10.5194/esd-2019-21 ◽

2019 ◽

Cited By ~ 3

Author(s):

Krishnamohan Krishna-Pillai Sukumara-Pillai ◽

Govindasamy Bala ◽

Long Cao ◽

Lei Duan ◽

Ken Caldeira

Keyword(s):

Radiative Forcing ◽

Stratospheric Aerosol ◽

System Response ◽

Substantial Part ◽

Aerosol Layer ◽

Sulfate Aerosols ◽

Cooling Effectiveness ◽

Aerosol Radiative Forcing ◽

Stratospheric Water Vapor ◽

Effective Radiative Forcing

Abstract. Reduction of surface temperatures of the planet by injecting sulfate aerosols in the stratosphere has been suggested as an option to reduce the amount of human-induced climate warming. Several previous studies have shown that for a specified amount of injection, aerosols injected at a higher altitude in the stratosphere would produce more cooling because aerosol sedimentation would take longer time. In this study, we isolate and assess the sensitivity to the altitude of the aerosol layer of stratospheric aerosol radiative forcing and the resulting climate change. We study this by prescribing a specified amount of sulfate aerosols, of a size typical of what is produced by volcanoes, distributed uniformly at different levels in the stratosphere. We find that stratospheric sulfate aerosols are more effective in cooling climate when they reside higher in the stratosphere. We explain this sensitivity in terms of effective radiative forcing: volcanic aerosols heat the stratospheric layers where they reside, altering stratospheric water vapor content, tropospheric stability and clouds, and consequently the effective radiative forcing. We show that the magnitude of the effective radiative forcing is larger when aerosols are prescribed at higher altitudes and the differences in radiative forcing due to fast adjustment processes can account for a substantial part of the dependence of amount of cooling on aerosol altitude. These altitude effects would be additional to dependences on aerosol microphysics, transport, and sedimentation, which are outside the scope of this study. The cooling effectiveness of stratospheric sulfate aerosols likely increases with altitude of the aerosol layer both because aerosols higher in the stratosphere have larger effective radiative forcing and because they have a longer stratospheric residence time; these two effects are likely to be of comparable importance.

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Stratospheric aerosol radiative forcing simulated by the chemistry climate model EMAC using Aerosol CCI satellite data

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-12845-2018 ◽

2018 ◽

Vol 18 (17) ◽

pp. 12845-12857 ◽

Cited By ~ 6

Author(s):

Christoph Brühl ◽

Jennifer Schallock ◽

Klaus Klingmüller ◽

Charles Robert ◽

Christine Bingen ◽

...

Keyword(s):

Optical Depth ◽

Radiative Forcing ◽

Volcanic Eruptions ◽

Stratospheric Aerosol ◽

Radiative Heating ◽

Aerosol Radiative Forcing ◽

Tropospheric Aerosol ◽

Model Aerosol ◽

Atmospheric Sounding ◽

Aerosol Radiative

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.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-10937-2017 ◽

2017 ◽

Vol 17 (18) ◽

pp. 10937-10953 ◽

Cited By ~ 4

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.

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Investigation of short-term effective radiative forcing of fire aerosols over North America using nudged hindcast ensembles

10.5194/acp-2017-414 ◽

2017 ◽

Author(s):

Yawen Liu ◽

Kai Zhang ◽

Yun Qian ◽

Yuhang Wang ◽

Yufei Zou ◽

...

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Analysis Data ◽

Ensemble Spread ◽

Short Term ◽

Large Ensemble ◽

Southern Mexico ◽

Aerosol Radiative Forcing ◽

Fire Emissions ◽

Effective Radiative Forcing

Abstract. Aerosols from fire emissions can potentially have large impact on clouds and radiation. However, fire aerosol sources are often intermittent and their effect on weather and climate is difficult to quantify. Here we investigated the short-term effective radiative forcing of fire aerosols using the global aerosol-climate model Community Atmosphere Model Version 5 (CAM5). Different from previous studies, we used nudged hindcast ensembles to quantify the forcing uncertainty due to the chaotic response to small perturbations in the atmosphere state. Daily mean emissions from three fire inventories were used to consider the uncertainty in emission strength and injection heights. The simulated aerosol optical depth (AOD) and mass concentrations were evaluated against in-situ measurements and re-analysis data. Overall, the results show the model has reasonably good predicting skills. Short (10-day) nudged ensemble simulations were then performed with and without fire emissions to estimate the effective radiative forcing. Results show fire aerosols have large effects on both liquid and ice clouds over the two selected regions in April 2009. For the 10-day average, we found a large ensemble spread of regional mean shortwave cloud radiative effect over Southern Mexico (15.6 %) and the Central U.S. (64.3 %), despite that the regional mean AOD time series are almost indistinguishable during the 10-day period. Moreover, the ensemble spread is much larger when using daily averages instead of 10-day averages. For the case investigated here, a minimum of 9 ensemble members is necessary to get a reasonable estimate of the ensemble mean and spread of the forcing on individual days. This demonstrates the importance of using a large ensemble of simulations to estimate the short-term effective aerosol radiative forcing.

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

Geoscientific Model Development ◽

10.5194/gmd-11-2581-2018 ◽

2018 ◽

Vol 11 (7) ◽

pp. 2581-2608 ◽

Cited By ~ 17

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.

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The impact of volcanic eruptions of different magnitude on stratospheric water vapor in the tropics

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-6565-2021 ◽

2021 ◽

Vol 21 (8) ◽

pp. 6565-6591

Author(s):

Clarissa Alicia Kroll ◽

Sally Dacie ◽

Alon Azoulay ◽

Hauke Schmidt ◽

Claudia Timmreck

Keyword(s):

Water Vapor ◽

Radiative Forcing ◽

Volcanic Eruptions ◽

Aerosol Layer ◽

Power Functions ◽

Max Planck ◽

Point Temperature ◽

Stratospheric Water Vapor ◽

Cold Point ◽

The Impact

Abstract. Increasing the temperature of the tropical cold-point region through heating by volcanic aerosols results in increases in the entry value of stratospheric water vapor (SWV) and subsequent changes in the atmospheric energy budget. We analyze tropical volcanic eruptions of different strengths with sulfur (S) injections ranging from 2.5 Tg S up to 40 Tg S using EVAens, the 100-member ensemble of the Max Planck Institute – Earth System Model in its low-resolution configuration (MPI-ESM-LR) with artificial volcanic forcing generated by the Easy Volcanic Aerosol (EVA) tool. Significant increases in SWV are found for the mean over all ensemble members from 2.5 Tg S onward ranging between [5, 160] %. However, for single ensemble members, the standard deviation between the control run members (0 Tg S) is larger than SWV increase of single ensemble members for eruption strengths up to 20 Tg S. A historical simulation using observation-based forcing files of the Mt. Pinatubo eruption, which was estimated to have emitted (7.5±2.5) Tg S, returns SWV increases slightly higher than the 10 Tg S EVAens simulations due to differences in the aerosol profile shape. An additional amplification of the tape recorder signal is also apparent, which is not present in the 10 Tg S run. These differences underline that it is not only the eruption volume but also the aerosol layer shape and location with respect to the cold point that have to be considered for post-eruption SWV increases. The additional tropical clear-sky SWV forcing for the different eruption strengths amounts to [0.02, 0.65] W m−2, ranging between [2.5, 4] % of the aerosol radiative forcing in the 10 Tg S scenario. The monthly cold-point temperature increases leading to the SWV increase are not linear with respect to aerosol optical depth (AOD) nor is the corresponding SWV forcing, among others, due to hysteresis effects, seasonal dependencies, aerosol profile heights and feedbacks. However, knowledge of the cold-point temperature increase allows for an estimation of SWV increases of 12 % per Kelvin increase in mean cold-point temperature. For yearly averages, power functions are fitted to the cold-point warming and SWV forcing with increasing AOD.

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Letter to the Editor Aerosol radiative forcing over land: effect of surface and cloud reflection

Annales Geophysicae ◽

10.5194/angeo-20-2105-2002 ◽

2002 ◽

Vol 20 (12) ◽

pp. 2105-2109 ◽

Cited By ~ 67

Author(s):

S. K. Satheesh

Keyword(s):

Optical Depth ◽

Atmospheric Aerosols ◽

Radiative Forcing ◽

Tropical Indian Ocean ◽

Atmospheric Composition ◽

Aerosol Layer ◽

Atmospheric Sciences ◽

Aerosol Radiative Forcing ◽

Aerosol Forcing ◽

Absorbing Aerosols

Abstract. It is now clearly understood that atmospheric aerosols have a significant impact on climate due to their important role in modifying the incoming solar and outgoing infrared radiation. The question of whether aerosol cools (negative forcing) or warms (positive forcing) the planet depends on the relative dominance of absorbing aerosols. Recent investigations over the tropical Indian Ocean have shown that, irrespective of the comparatively small percentage contribution in optical depth ( ~ 11%), soot has an important role in the overall radiative forcing. However, when the amount of absorbing aerosols such as soot are significant, aerosol optical depth and chemical composition are not the only determinants of aerosol climate effects, but the altitude of the aerosol layer and the altitude and type of clouds are also important. In this paper, the aerosol forcing in the presence of clouds and the effect of different surface types (ocean, soil, vegetation, and different combinations of soil and vegetation) are examined based on model simulations, demonstrating that aerosol forcing changes sign from negative (cooling) to positive (warming) when reflection from below (either due to land or clouds) is high.Key words. Atmospheric composition and structure (aerosols and particles) History of Geophysics (atmospheric sciences) Hydrology (anthropogenic effects)

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Impact of the Ambae, Raikoke and Ulawun eruptions in 2018-2019 on the global stratospheric aerosol layer and climate

10.5194/egusphere-egu2020-2406 ◽

2020 ◽

Author(s):

Corinna Kloss ◽

Pasquale Sellitto ◽

Bernard Legras ◽

Jean-Paul Vernier ◽

Fabrice Jégou ◽

...

Keyword(s):

Radiative Transfer ◽

Radiative Forcing ◽

Volcanic Eruptions ◽

Stratospheric Aerosol ◽

Orthogonal Polarization ◽

Transfer Model ◽

Aerosol Layer ◽

The Impact ◽

Aerosol Plume

Using a combination of satellite, ground-based and in-situ observations, and radiative transfer modelling, we quantify the impact of the most recent moderate volcanic eruptions (Ambae, Vanuatu in July 2018; Raikoke, Russia and Ulawun, New Guinea in June 2019) on the global stratospheric aerosol layer and climate.For the Ambae volcano (15&#176;S and 167&#176;E), we use the Stratospheric Aerosol and Gas Experiment III (SAGE III), the Ozone Mapping Profiler Suite (OMPS), the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Himawari geostationary satellite observations of the aerosol plume evolution following the Ambae eruption of July 2018. It is shown that the aerosol plume of the main eruption at Ambae in July 2018 was distributed throughout the global stratosphere within the global large-scale circulation (Brewer-Dobson circulation, BDC), to both hemispheres. Ground-based LiDAR observations in Gadanki, India, as well as in-situ Printed Optical Particle Spectrometer (POPS) measurements acquired during the BATAL campaign confirm a widespread perturbation of the stratospheric aerosol layer due to this eruption. Using the UVSPEC radiative transfer model, we also estimate the radiative forcing of this global stratospheric aerosol perturbation. The climate impact is shown to be comparable to that of the well-known and studied recent moderate stratospheric eruptions from Kasatochi (USA, 2008), Sarychev (Russia, 2009) and Nabro (Eritrea, 2011). Top of the atmosphere radiative forcing values between -0.45 and -0.60 W/m2, for the Ambae eruption of July 2018, are found.In a similar manner the dispersion of the aerosol plume of the Raikoke (48&#176;N and 153&#176;E) and Ulawun (5&#176;S and 151&#176;E) eruptions of June 2019 is analyzed. As both of those eruptions had a stratospheric impact and happened almost simultaneously, it is challenging to completely distinguish both events. Even though the eruptions occurred very recently, first results show that the aerosol plume of the Raikoke eruption resulted in an increase in aerosol extinction values, double as high as compared to that of the Ambae eruption. However, as the eruption occurred on higher latitudes, the main bulk of Raikoke aerosols was transported towards the northern higher latitude&#8217;s in the stratosphere within the BDC, as revealed by OMPS, SAGE III and a new detection algorithm for SO2 and sulfate aerosol using IASI (Infrared Atmospheric Sounder Interferometer). Even though the Raikoke eruption had a larger impact on the stratospheric aerosol layer, both events (the eruptions at Raikoke and Ambae) have to be considered in stratospheric aerosol budget and climate studies.

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Composition Dependence of Stratospheric Aerosol Radiative Forcing

10.5194/egusphere-egu21-13162 ◽

2021 ◽

Author(s):

Yaowei Li ◽

John Dykema ◽

Frank Keutsch

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Radiative Forcing ◽

Complex Refractive Index ◽

Stratospheric Aerosol ◽

Organic Component ◽

Aerosol Optical Properties ◽

Aerosol Radiative Forcing ◽

Aerosol Radiative

Model results suggest organic aerosol represents a significant fraction of total stratospheric aerosol radiative forcing, which in itself could represent as much as a quarter of global radiative forcing. Other model investigations suggest that the radiative influence of organic aerosols and dust must be included to obtain consistency with satellite measurements of stratospheric aerosols. In situ observations suggest that stratospheric aerosol composition is strongly vertically dependent and contains a significant organic component in the lower stratosphere. Laboratory studies suggest a range of possible values for the complex refractive index of organic aerosols in the stratosphere. The real part of the refractive index could vary over a range that brackets the value of the real refractive index for pure sulfuric acid/water aerosols. The imaginary part of the refractive index of the organic component is highly uncertain, suggesting aerosols that range from being purely refractive to significantly absorbing (eg, brown carbon). The mixing state of these mixed composition aerosols is also uncertain; depending on the complex refractive index of the organic component, morphological variation could have a significant influence on aerosol radiative properties. In this work we perform a sensitivity study of shortwave radiative forcing of stratospheric aerosols, examining the influence of different plausible values of complex refractive index and particle morphologies. In situ measurements of aerosol size and composition are used to represent the size distribution, vertical profile, and organic mass fraction for the computation of aerosol optical properties. These profiles of aerosol optical properties are used as inputs to a radiative transfer model to calculate profiles of shortwave fluxes and radiative heating rates for standard model atmospheres. The implications of the variations in aerosol optical depth and resulting radiative forcing are interpreted in terms of implications for satellite measurements of stratospheric radiative forcing. The various radiative forcing results and remote sensing implications for different scenarios of organic complex refractive index and morphology call for better understandings of the effects of chemical evolution and transport dynamics on the aerosol optical properties in the stratosphere.

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

10.5194/gmd-2017-308 ◽

2018 ◽

Cited By ~ 3

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 sulphur 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 4 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 sulphur emissions and transport processes over the period 1998–2012 and their role in the warming hiatus. Two further experiments will investigate the stratospheric sulphate 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.

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Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer