Understanding volcano-climate impacts and the stratospheric aerosol layer 

Volcanic aerosol clouds from major tropical eruptions cause periods of strong surface cooling in the historical climate record and are dominant influences within decadal surface temperature trends.

Even the transition from the unusual 1998-2002 period of a “fully decayed to quiescence” stratospheric aerosol layer, into a more typical period of modest volcanic activity temporarily offset a substantial proportion of the subsequent decadal forcing from increased greenhouse gases.

Advancing our understanding of the influence of volcanoes on climate relies upon better knowledge of (i) the radiative forcings of past eruptions and the microphysical, chemical and dynamical processes which affect the evolution of stratospheric aerosol properties and (ii) the response mechanisms governing post-eruption climate variability and their dependency on the climate state at the time of the eruption. This can only be achieved by combining information from satellite and in-situ observations of recent eruptions, stratospheric aerosol and climate modelling activities, and reconstructions of past volcanic histories and post-eruption climate state from proxies.

In recent years the smoke from intense wildfires in North America and Australia has also been an important component of the stratospheric aerosol layer, the presence of organic aerosol and meteoric particles in background conditions now also firmly established.

This session seeks presentations from research aimed at better understanding the stratospheric aerosol layer, its volcanic perturbations and the associated impacts on climate through the post-industrial period (1750-present) and also those further back in the historical record.

We also welcome contributions to understand the societal impacts of volcanic eruptions and the human responses to them. Contributions addressing volcanic influences on atmospheric composition, such as changes in stratospheric water vapour, ozone and other trace gases are also encouraged.

The session aims to bring together research contributing to several current international co-ordinated activities: SPARC-SSiRC, CMIP6-VolMIP, CMIP6-PMIP, and PAGES-VICS.

Co-organized by CL4/NH2, co-sponsored by SPARC-SSiRC and CMIP6-VolMIP
Convener: Graham Mann | Co-conveners: Myriam Khodri, Claudia Timmreck, Matthew Toohey, Davide Zanchettin
vPICO presentations
| Tue, 27 Apr, 09:00–12:30 (CEST)

vPICO presentations: Tue, 27 Apr

Chairpersons: Myriam Khodri, Davide Zanchettin, Graham Mann
Krakatau and 19th century volcanic forcing/climate-response
Elizaveta Malinina and Nathan Gillett

Volcanic eruptions are an important driver of climate variability. Multiple literature sources have shown that after large explosive eruptions there is a decrease in global mean temperature, caused by an increased amount of stratospheric aerosols which influence the global radiative budget. In this study, we investigate the changes in several climate variables after a volcanic eruption. Using ESMValTool (Earth System Model Evaluation Tool) on an ensemble of historical simulations from CMIP6, such variables as global mean surface temperature (GMST), Arctic sea ice area and Nino 3.4 index were analyzed following the 1883 Krakatoa eruption. While there is a definite decrease in the multi-model mean GMST after the eruption, other indices do not show as prominent change. The reasons for this behavior are under investigation. 

How to cite: Malinina, E. and Gillett, N.: Climate variability following large volcanic eruption: CMIP6 model investigation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3686,, 2021.

Rafael Castro, Tushar Mittal, and Stephen Self

The 1883 Krakatau eruption is one of the most well-known historical volcanic eruptions due to its significant global climate impact as well as first recorded observations of various aerosol associated optical and physical phenomena. Although much work has been done on the former by comparison of global climate model predictions/ simulations with instrumental and proxy climate records, the latter has surprisingly not been studied in similar detail. In particular, there is a wealth of observations of vivid red sunsets, blue suns, and other similar features, that can be used to analyze the spatio-temporal dispersal of volcanic aerosols in summer to winter 1883. Thus, aerosol cloud dispersal after the Krakatau eruption can be estimated, bolstered by aerosol cloud behavior as monitored by satellite-based instrument observations after the 1991 Pinatubo eruption. This is one of a handful of large historic eruptions where this analysis can be done (using non-climate proxy methods). In this study, we model particle trajectories of the Krakatau eruption cloud using the Hysplit trajectory model and compare our results with our compiled observational dataset (principally using Verbeek 1884, the Royal Society report, and Kiessling 1884).

In particular, we explore the effect of different atmospheric states - the quasi-biennial oscillation (QBO) which impacts zonal movement of the stratospheric volcanic plume - to estimate the phase of the QBO in 1883 required for a fast-moving westward cloud. Since this alone is unable to match the observed latitudinal spread of the aerosols, we then explore the impact of an  umbrella cloud (2000 km diameter) that almost certainly formed during such a large eruption. A large umbrella cloud, spreading over ~18 degrees within the duration of the climax of the eruption (6-8 hours), can lead to much quicker latitudinal spread than a point source (vent). We will discuss the results of the combined model (umbrella cloud and correct QBO phase) with historical accounts and observations, as well as previous work on the 1991 Pinatubo eruption. We also consider the likely impacts of water on aerosol concentrations and the relevance of this process for eruptions with possible significant seawater interactions, like Krakatau. We posit that the role of umbrella clouds is an under-appreciated, but significant, process for beginning to model the climatic impacts of large volcanic eruptions.

How to cite: Castro, R., Mittal, T., and Self, S.: Revisiting the Krakatau 1883 Volcanic Aerosol Dispersal , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10489,, 2021.

Thomas Aubry, Anja Schmidt, Alix Harrow, Jeremy Walton, Jane Mulcahy, Fiona O'Connor, Colin Jones, Steven Rumbold, Lauren Marshall, and Luke Abraham

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.

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’s historical runs.

How to cite: Aubry, T., Schmidt, A., Harrow, A., Walton, J., Mulcahy, J., O'Connor, F., Jones, C., Rumbold, S., Marshall, L., and Abraham, L.: Volcanic forcing of climate since 1850 in an interactive aerosol-chemistry-climate model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10070,, 2021.

Shih-Wei Fang, Claudia Timmreck, Johann Jungclaus, and Hauke Schmidt

Volcanic eruptions and reduced solar radiance can individually cool our globe through both direct changes in incoming radiation and indirect influences from dynamical processes. However, whether the cooling from the combination of two forcing can be linearly additive, or if additional cooling exists when reduced solar radiance is imposed during volcanic eruptions remains unclear. In this project, by using the state-of-art climate model (MPI-ESM1-2-LR), we found that the total cooling of the two forcing can be additive, but also have additional cooling during the period when volcanic cooling bouncing back to climatology. Our experiments focus on the early 19th century (1791-1850) since the period existed multiple strong volcanic events (especially the 1809 unidentified eruption and 1815 Tambora eruption), a solar minimum (Dalton minimum from 1790-1830), and limited influence from anthropogenic greenhouse gases. In the presentation, we will discuss how volcanic eruptions and different amplitudes of solar reconstructions can individually and together cool the surface through both direct radiative changes and dynamical influences. Our main focus will be how the atmospheric circulation may influence the polar sea ice and large-scale climate patterns when imposing combinations of solar and volcanic forcing.

How to cite: Fang, S.-W., Timmreck, C., Jungclaus, J., and Schmidt, H.: The Interplay between Volcanic and Solar Cooling in the Early 19th Century, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10277,, 2021.

Claudia Timmreck, Matthew Toohey, Davide Zanchettin, Stefan Brönnimann, Elin Lundstadt, and Robert Wilson

The  "1809 eruption” is one of the most recent unidentified volcanic eruptions with a global climate impact. Even though the eruption ranks as the 3rd largest since 1500 with an eruption magnitude estimated to be two times that of the 1991 eruption of Pinatubo, not much is known of it from historic sources. Based on a compilation of instrumental and reconstructed temperature time series, we show here that tropical temperatures show a significant drop in response to the ~1809 eruption, similar to that produced by the Mt. Tambora eruption in 1815, while the response of Northern Hemisphere (NH) boreal summer temperature is spatially heterogeneous.  Here, we present the sensitivity of the climate response simulated by the MPI Earth system model to a range of volcanic forcing estimates constructed using estimated volcanic stratospheric sulfur injections (VSSI) and uncertainties from ice core records. Three of the forcing reconstructions represent a tropical eruption with approximately symmetric hemispheric aerosol spread but different forcing magnitudes, while a fourth reflects a hemispherically asymmetric scenario without volcanic forcing in the NH extratropics. Observed and reconstructed post-volcanic surface NH summer temperature anomalies lie within the range of all the scenario simulations. Therefore, assuming the model climate sensitivity is correct, the VSSI estimate is accurate within the uncertainty bounds. Comparison of observed and simulated tropical temperature anomalies suggests that the most likely VSSI for the 1809 eruption would be somewhere between 12 -19 Tg of sulfur. Model results show that NH large-scale climate modes are sensitive to both volcanic forcing strength and its spatial structure.  While spatial correlations between the N-TREND NH temperature reconstruction and the model simulations are weak in terms of the ensemble mean model results, individual model simulations show good correlation over North America and Europe, suggesting the spatial heterogeneity of the 1810 cooling could be due to internal climate variability. 

How to cite: Timmreck, C., Toohey, M., Zanchettin, D., Brönnimann, S., Lundstadt, E., and Wilson, R.: The unidentified volcanic eruption of ~1809: why it remains a climatic cold case, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5330,, 2021.

ENSO variability and volcanic impacts on monsoons
Feng Zhu, Julien Emile-Geay, Kevin Anchukaitis, Greg Hakim, Andrew Wittenberg, Mariano Morales, and Jonathan King

The potential for explosive volcanism to affect the state of the El Niño-Southern Oscillation (ENSO) has been debated since the 1980s. Several observational studies, largely based on tree rings, have since found support for a positive ENSO phase in the year following large eruptions. Models of different complexities also simulate such a response, detectable above the backdrop of internal variability – though they disagree on the underlying mechanisms. In contrast, recent coral data from the heart of the tropical Pacific suggest no uniform ENSO response to all eruptions over the last millennium. Here we leverage paleoclimate data assimilation to integrate the latest paleoclimate evidence into a consistent dynamical framework and re-appraise this relationship. Our analysis finds only a weak statistical association between volcanism and ENSO, suggestive of either no causal association, or of an insufficient number of large volcanic events over the past millennium to obtain reliable statistics. While currently available observations do not support the model-based inference that tropical eruptions promote an ENSO response, there are hints of a response to hemispherically asymmetric forcing, consistent with the "ITCZ shift" mechanism. We discuss the difficulties of conclusively establishing a volcanic influence on ENSO given the many degrees of freedom affecting the response, including eruption season, spatial characteristics of the forcing, and ENSO phase preconditioning.

How to cite: Zhu, F., Emile-Geay, J., Anchukaitis, K., Hakim, G., Wittenberg, A., Morales, M., and King, J.: Volcanoes and ENSO: a re-appraisal with the Last Millennium Reanalysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-753,, 2021.

Manmeet Singh, Raghavan Krishnan, Bedartha Goswami, Ayantika Dey Choudhury, Swapna Panickal, Ramesh Vellore, Prajeesh A Gopinathan, Sandeep Narayanasetti, Chandra Venkataraman, Reik V Donner, Norbert Marwan, and Jürgen Kurths

The coupling between the El Niño–Southern Oscillation (ENSO) and Indian Monsoon (IM) plays a significant role in the summer rainfall over the Indian subcontinent. In this study, we provide insights into the IM variability with regard to the degree of ENSO variability and radiative forcing from large volcanic eruptions (LVEs). Volcanic dust and gas injected into the stratosphere during major eruptions influence the ENSO from seasonal to interannual timescales. However, the effects of LVEs on the ENSO-IM coupling remain unclear. The relationship between ENSO and IM systems in the context of LVEs is examined using a panoply of datasets and advanced statistical analysis techniques in this study. We find that there is a significant enhancement of the phase-synchronization between ENSO and IM oscillations due to increase in angular frequency of ENSO in the last millennium. Twin surrogates-based statistical significance testing is also used to affirm this result and similar evidence is found in the combinations of 14 ENSO and 11 IM paleoclimate proxy records in the last millennium. Bayesian probabilities conditioned with and without LVEs show LVEs lead to a strong ENSO-IM phase-coupling, with the probabilities remaining higher till the fourth year from the eruption. A large-ensemble climate model experiment with and without the 1883 Krakatoa eruption is conducted using the IITM-ESM, and also with varied volcanic radiative forcing (VRF) depending on the evolved state of ENSO. The simulations show that LVEs force the ENSO-IM systems into a coupled state, and increase (decrease) in the VRF leads to an enhanced (decreased) probability of the phase synchronisation of ENSO-IM systems with a high chance of El Niño-IM drought in the year following the LVE. Our results promisingly pave a way not only for improving the seasonal monsoon prediction improvements but also for the regional impact assessment from the proposed geo-engineering activities over the South Asian region.

How to cite: Singh, M., Krishnan, R., Goswami, B., Choudhury, A. D., Panickal, S., Vellore, R., Gopinathan, P. A., Narayanasetti, S., Venkataraman, C., Donner, R. V., Marwan, N., and Kurths, J.: Fingerprint of volcanic forcing on the ENSO–Indian monsoon coupling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9059,, 2021.

Keith Potts

Volcanic aerosols over south east Asia have always been the trigger and sustaining cause of ENSO events. In recent decades this natural plume has been augmented by the anthropogenic plume which has intensified ENSO events especially in SON. Data from the Last Millennium Ensemble (13,872 months), and Large Ensemble (3,012 months) demonstrate this connection with three ENSO indices and aerosol data derived from the same datasets correlating at 1.00 (LME), 0.97 and 0.99 magnitude (segmented and averaged). ENSO events are the dominant mode of variability in the global climate responsible for Australian, Indian and Indonesian droughts, American floods and increased global temperatures. Understanding the mechanism which enables aerosols over SE Asia and only over SE Asia to create ENSO events is crucial to understanding the global climate. I show that the South East Asian aerosol Plume causes ENSO events by: reflecting/absorbing solar radiation which warms the upper troposphere; and reducing surface radiation which cools the surface under the plume. This inversion reduces convection in the region thereby suppressing the Walker Circulation and the Trade Winds which causes the SST to rise in the central Pacific Ocean and creates convection there. This further weakens/reverses the Walker Circulation driving the climate into an ENSO state which is maintained until the aerosols dissipate and the climate system relaxes into a non-ENSO state. Measured aerosol data from four NASA satellites, estimates of volcanic tephra from the Global Volcanism Program (GVP) for over 100 years and the NASA MERRA-2 reanalysis dataset all confirm this analysis.

How to cite: Potts, K.: How Extreme Apparitions of the Volcanic and Anthropogenic South East Asian Aerosol Plume Trigger and Sustain El Niño events using data from the Last Millennium Ensemble, Large Ensemble, MERRA-2 Reanalysis, four Satellites and the Global Volcanism P, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6743,, 2021.

Seungmok Paik, Seung-Ki Min, Carley E. Iles, Erich M. Fischer, and Andrew P. Schurer

This study identifies a crucial cause of the large uncertainty in global precipitation response after volcanic eruptions. We find an important contribution of diverse El Niño responses to the inter-simulation spread in the global monsoon drying responses to tropical eruptions. Most Coupled Model Intercomparison Project Phase 5 (CMIP5) models simulate El Niño–like equatorial eastern Pacific warming at the year after eruptions but with different amplitudes, which drive a large spread of summer monsoon weakening and corresponding precipitation reduction. Two factors are further identified for the diverse El Niño responses among CMIP5 model simulations. First, difference in imposed volcanic forcings induces systematic differences in the Maritime Continent precipitation drying and subsequent westerly winds over equatorial western Pacific, accounting for a large portion (29%) of inter-simulation spread in El Niño intensities following eruptions. In addition, the internally generated warm water volume over the equatorial western Pacific in the pre-eruption month also contributes to the diverse El Niño development, explaining about 14% of the total inter-simulation variance through the recharge oscillator mechanism. Our findings based on CMIP5 multi-model simulations confirm that reliable estimates of the volcanic forcing magnitude as well as the pre-eruption oceanic condition are required to obtain more reliable simulations or predictions of the hydrological responses to tropical eruptions.

How to cite: Paik, S., Min, S.-K., Iles, C. E., Fischer, E. M., and Schurer, A. P.: Volcanic-induced global monsoon drying modulated by diverse El Niño responses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13993,, 2021.

Meng Zuo, Tianjun Zhou, and Wenmin Man

Both proxy data and climate modeling show divergent responses of global monsoon precipitation to volcanic eruptions. The reason is however unknown. Here, based on analysis of the CESM Last Millennium Ensemble simulation, we show evidences that the divergent responses are dominated by the pre-eruption background oceanic states. We found that under El Niño-Southern Oscillation (ENSO) neutral and warm phases initial conditions, the Pacific favors an El Niño-like anomaly after volcanic eruptions, while La Niña-like SST anomalies tend to occur following eruptions under ENSO cold phase initial condition, especially after southern eruptions. The cold initial condition is associated with stronger upper ocean temperature stratification and shallower thermocline over the eastern Pacific than normal. The easterly anomalies triggered by surface cooling over the tropical South America continent can generate changes in SST through anomalous advection and the ocean subsurface upwelling more efficiently, causing La Niña-like SST anomalies. Whereas under warm initial condition, the easterly anomalies fail to develop and the westerly anomalies still play a dominant role, thus forms an El Niño-like SST anomaly. Such SST response further regulates the monsoon precipitation changes through atmospheric teleconnection. The contribution of direct radiative forcing and indirect SST response to precipitation changes show regional differences, which will further affect the intensity and sign of precipitation response in submonsoon regions. Our results imply that attention should be paid to the background oceanic state when predicting the global monsoon precipitation responses to volcanic eruptions.

How to cite: Zuo, M., Zhou, T., and Man, W.: Dependence of global monsoon response to volcanic eruptions on the background oceanic states, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1003,, 2021.

Major volcanic aerosol clouds: strat-heating, transport/residence-time and volcanic ash
Ilaria Quaglia, Christoph Brühl, Sandip Dhomse, Henning Franke, Anton Laakso, Graham Mann, Micheal Mills, Ulrike Niemeier, Giovanni Pitari, Timofei Sukhodolov, Claudia Timmreck, Paolo Tuccella, and Daniele Visioni

Large magnitude tropical volcanic eruptions emit sulphur dioxide and other gases directly into the stratosphere, creating a long-lived volcanic aerosol cloud which scatter incoming solar radiation, absorbs outgoing terrestrial radiation, and can strongly affect the composition of the stratosphere.

Such major volcanic enhancements of the stratospheric aerosol layer have strong “direct effects” on climate via these influences on radiative transfer, primarily surface cooling via the reduced insolation, but also have a range of indirect effects, due to the volcanic aerosol cloud’s effects on stratospheric circulation, dynamics and chemistry.

In this study, we investigate the 3 largest volcanic enhancements to the stratospheric aerosol layer in the last 100 years (Mt Agung 1963; Mt El Chichón 1982; Mt Pinatubo 1991), comparing co-ordinated simulations within the so-called HErSEA experiments (Historical Eruptions SO2 Emission Assessment) several national climate modelling centres carried out for the model intercomparison project ISA-MIP.

The HErSEA experiment saw participating models performing interactive stratospheric aerosol simulations of each of the volcanic aerosol clouds with common upper-, mid- and lower-estimate amounts and injection heights of sulfur dioxide, in order to better understand known differences among modelling studies for which initial emission gives best agreement with observations. 

First, we compare results of several models HErSEA simulations with a range of observations, with the aim to find where there is agreement between the models and where there are differences, at the different initial sulfur injection amount and altitude distribution.

In this way, we could understand the differences and limitations in the mechanisms that controls the dynamical, microphysical and chemical processes of stratospheric aerosol layer.

How to cite: Quaglia, I., Brühl, C., Dhomse, S., Franke, H., Laakso, A., Mann, G., Mills, M., Niemeier, U., Pitari, G., Sukhodolov, T., Timmreck, C., Tuccella, P., and Visioni, D.: Interactive Stratospheric Aerosol models response to different sulfur injection amount and altitude distribution during volcanic eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13387,, 2021.

Zhihong Zhuo, Herman Fuglestvedt, Matthew Toohey, Michael J. Mills, and Kirstin Krüger

Major volcanic eruptions increase sulfate aerosols in the stratosphere. This causes a large-scale dimming effect with significant surface cooling and stratosphere warming. However, the climate impact differs for tropical and extratropical eruptions, and depends on the eruption season and height, and volcanic volatiles injections. In order to study different volcanic aerosol forcing and their climate impact, we perform simulations based on the fully coupled Community Earth System Model version 2 (CESM2) with the version 6 of the Whole Atmosphere Community Climate Model (WACCM6) with prognostic stratospheric aerosol and chemistry. In this study, explosive eruptions at 14.6 N and 63.6 N in January and July injecting 17 MT and 200 MT SO2 at 24 km with and without halogens are simulated, in line with Central American Volcanic Arc and Icelandic volcanic eruptions. Simulated changes in the stratospheric sulfate and halogen burdens, and related impacts on aerosol optical depth, radiation, ozone and surface climate are analyzed. These simulated volcanic eruption cases will be compared with simulations based on the aerosol-climate model MAECHAM5-HAM.

How to cite: Zhuo, Z., Fuglestvedt, H., Toohey, M., Mills, M. J., and Krüger, K.: Model comparison of volcanic aerosol forcing and climate impact of tropical and extratropical eruptions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15581,, 2021.

Herman Fuglestvedt, Zhihong Zhuo, Michael Sigl, Matthew Toohey, Michael Mills, and Kirstin Krüger

Large explosive volcanic eruptions inject sulphur into the stratosphere where it is converted to sulphur dioxide and sulphate aerosols. Due to atmospheric circulation patterns, aerosols from high-latitude eruptions typically remain concentrated in the hemisphere in which they are injected. Eruptions in the high-latitude Northern Hemisphere could thus lead to a stronger hemispheric radiative forcing and surface climate response than tropical eruptions, a claim that is supported by a previous study based on proxy records and the coupled aerosol-general circulation model MAECHAM5-HAM. Additionally, the subsequent surface deposition of volcanic sulphate is potentially harmful to humans and ecosystems, and an improved understanding of the deposition over polar ice sheets can contribute to better reconstructions of historical volcanic forcing. On this basis, we model Icelandic explosive eruptions in a pre-industrial atmosphere, taking both volcanic sulphur and halogen loading into account. We use the fully coupled Earth system model CESM2 with the atmospheric component WACCM6, which extends to the lower thermosphere and has prognostic stratospheric aerosols and full chemistry. In order to study the volcanic impacts on the atmosphere, environment, and sulphate deposition, we vary eruption parameters such as sulphur and halogen loading, and injection altitude and season. The modelled volcanic sulphate deposition is compared to the deposition in ice cores following comparable historical eruptions. Furthermore, we evaluate the potential environmental impacts of sulphate deposition. To study inter-model differences, we also compare the CESM2-WACCM6 simulations to similar Icelandic eruption experiments simulated with MAECHAM5-HAM. 

How to cite: Fuglestvedt, H., Zhuo, Z., Sigl, M., Toohey, M., Mills, M., and Krüger, K.: Modelling high-latitude explosive eruptions and their atmospheric and environmental impacts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15780,, 2021.

Jesper Sjolte, Florian Adolphi, Hera Guðlaugsdòttir, and Raimund Muscheler

Major volcanic eruptions have a cooling effect on Earth's climate. In addition, low latitude volcanic eruptions can impact atmospheric circulation leading to a positive North Atlantic Oscillation index (NAO) during the subsequent winters. However, the question of the climate effect of high latitude eruptions, and whether volcanic eruptions impact atmospheric circulation during summer has received less attention. Here we show that high latitude eruptions lead to negative NAO during winter and summer. In addition, our analysis of novel climate field reconstructions supports the long-lasting positive winter NAO pattern for up to 5 years after major low latitude eruptions in agreement with earlier reconstructions and model experiments. Furthermore, we demonstrate a positive NAO during summer following low-latitude eruptions. The differences in the effect of high- and low-latitude eruptions on atmospheric circulation and regional temperature provide important insights for the understanding of past and future climate changes in response to volcanic forcing.

How to cite: Sjolte, J., Adolphi, F., Guðlaugsdòttir, H., and Muscheler, R.: Major differences in regional climate impact between high- and low latitude volcanic eruptions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8437,, 2021.

Laura Crick, Andrea Burke, William Hutchison, Stephen Sparks, Sue Mahony, Eric W. Wolff, Emily A. Doyle, James W. B. Rae, Joel Savarino, Mika Kohno, Sepp Kipfstuhl, and Gerhard Wörner

The ~74ka Toba eruption in Indonesia was one of the largest volcanic events of the Quaternary and loaded an estimated 100 million tonnes of H2SO4 into the atmosphere. Understanding the precise timing of this colossal eruption is vital to unravelling the climatic and environmental impacts of the largest volcanic events on Earth. Sulfur aerosols injected into the stratosphere following large volcanic events scatter incoming radiation and lead to global cooling, and in the case of Toba it has been suggested that it led to cooling of 1 – 5°C and extinctions of some local hominin populations. One of the most enigmatic features of the Toba eruption is that the S peak has yet to be identified in the ice core records, although numerous candidate sulfate peaks have been identified in both Arctic and Antarctic ice cores. To address this, we analysed the sulfur isotope fingerprint (δ34S and Δ33S) of 11 Toba candidates from two Antarctic ice cores by multi-collector inductively coupled plasma mass spectrometry. This approach allows us to evaluate injection altitudes and to distinguish large tropical eruptions from proximal eruptions because stratospheric sulfur aerosols undergo UV photochemical reactions that impart a sulfur mass-independent isotopic fractionation (S-MIF). In contrast, tropospheric sulfur aerosols do not exhibit S-MIF because they are shielded from the relevant UV radiation by the ozone layer.

We identify three stratospheric, tropical eruption candidates with two recording the largest Δ33S signals measured to date in the ice core archives. The largest of these Δ33S signals is >2 ‰ more negative than previous measurements of the 1257 Samalas eruption (the largest eruption of the last 2000 years), despite having a similar integrated sulfate flux for this event to the ice core. These three candidates are within uncertainly of the Ar40/Ar39 age estimates for the Toba eruption and when considered with other paleoclimate proxies place the event during the transition into Greenland Stadial 20.  Finally, we further analyse the relationship between the Toba eruption candidates and these proxies to determine the precise timing and potential climatic impacts of one of the largest eruptions of the Quaternary period.

How to cite: Crick, L., Burke, A., Hutchison, W., Sparks, S., Mahony, S., Wolff, E. W., Doyle, E. A., Rae, J. W. B., Savarino, J., Kohno, M., Kipfstuhl, S., and Wörner, G.: New insights into the ~74 ka Toba eruption from sulfur isotopes of polar ice cores, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6495,, 2021.

Matthew Toohey, Yue Jia, and Susann Tegetmeier

The cumulative radiative impact of major volcanic eruptions depends strongly on the length of time volcanic sulfate aerosol remains in the stratosphere. Observations of aerosol from recent eruptions have been used to suggest that residence time depends on the latitude of the volcanic eruption, with tropical eruptions producing aerosol loading that persists longer than that from extratropical eruptions. However, the limited number of eruptions observed make it difficult to disentangle the roles of latitude and injection height in controlling aerosol lifetime. Here we use satellite observations and model experiments to explore the relationship between eruption latitude, injection height and resulting residence time of stratospheric aerosol. We find that contrary to earlier interpretations of observations, the residence time of aerosol from major tropical eruptions like Pinatubo (1991) is on the order of 24 months. Model results suggest that the residence time is greatly sensitive to the height of the sulfur injection, especially within the lowest few kilometers of the stratosphere. As injection heights and latitudes are unknown for the majority of eruptions over the common era, we estimate the impact of this uncertainty on volcanic aerosol forcing reconstructions. 

How to cite: Toohey, M., Jia, Y., and Tegetmeier, S.: Stratospheric residence time and the lifetime of volcanic aerosol, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12131,, 2021.

Clarissa Kroll, Hauke Schmidt, and Claudia Timmreck

Large volcanic eruptions affect the distribution of atmospheric water vapour, for instance through cooling of the surface, warming of the lowermost stratosphere, and increasing the upwelling in the tropical tropopause region.

To better understand the volcanic impact on the tropical tropopause region and associated changes in the water vapour distribution in the stratosphere we employ a combination of short term convection-resolving global simulations with ICON and long term low resolution ensemble simulations with the MPI-ESM1.2-LR EVAens, both with prescribed volcanic forcing. With the EVAens a long term statistical analysis of the water vapour trends during the build-up and decay of a volcanic aerosol layer is made possible. The impact of the heating in the cold point regions is studied for five different eruption magnitudes. Stratospheric water vapour changes are analyzed in simulations with synthetic and observation based aerosol profiles showing that the distance of the aerosol profile from the cold point region can be more important for the water vapour entry into the stratosphere than the emitted amount of sulfur.

Whereas the EVAens is ideal to investigate the slow ascent of water vapour into the stratosphere the 10 km high resolution simulations with ICON allow insights into the convective changes after volcanic eruptions going beyond the limitations parameterizations usually impose on the model data.

How to cite: Kroll, C., Schmidt, H., and Timmreck, C.: Volcanic aerosol heating in the tropical tropopause region and associated water vapour changes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12318,, 2021.

Juan Carlos Antuña-Marrero, Graham W. Mann, John Barnes, Albeth Rodríguez-Vega, Sarah Shallcross, Sandip Dhomse, Giorgio Fiocco, and Gerald W. Grams

We report the recovery and processing methodology of the first ever multi-year lidar dataset of the stratospheric aerosol layer. A Q-switched Ruby lidar measured 66 vertical profiles of 694nm attenuated backscatter at Lexington, Massachusetts between January 1964 and August 1965, with an additional 9 profile measurements conducted from College, Alaska during July and August 1964.

We describe the processing of the recovered lidar backscattering ratio profiles to produce mid-visible (532nm) stratospheric aerosol extinction profiles (sAEP532) and stratospheric aerosol optical depth (sAOD532) measurements.

Stratospheric soundings of temperature, and pressure generate an accurate local molecular backscattering profile, with nearby ozone soundings determining the ozone absorption, those profiles then used to correct for two-way ozone transmittance. Two-way aerosol transmittance corrections were also applied based on nearby observations of total aerosol optical depth (across the troposphere and stratosphere) from sun photometer measurements.

We show the two-way transmittance correction has substantial effects on the retrieved sAEP532 and sAOD532, calculated without the corrections resulting in substantially lower values of both variables, as it was not applied in the original processing producing the lidar scattering ratio profiles we rescued. The combined transmittance corrections causes the aerosol extinction to increase by 67 % for Lexington and 27 % for Fairbanks, for sAOD532 the increases 66 % and 26 % respectively. Comparing the magnitudes of the aerosol extinction and sAOD with the few contemporary available measurements reported show a better agreement in the case of the two way transmittance corrected values.

The sAEP and sAOD timeseries at Lexington show a surprisingly large degree of variability, three periods where the stratospheric aerosol layer had suddenly elevated optical thickness, the highest sAOD532 of 0.07 measured at the end of March 1965. The two other periods of enhanced sAOD532 are both two-month periods where the lidars show more than 1 night where retrieved sAOD532 exceeded 0.05: in January and February 1964 and November and December 1964.

Interactive stratospheric aerosol model simulations of the 1963 Agung cloud illustrate that although substantial variation  in mid-latitude sAOD532 is expected from the seasonal cycle in the Brewer-Dobson circulation, the Agung cloud dispersion will have caused much slower increase than the more episodic variations observed, with also different timing, elevated optical thickness from Agung occurring in winter and spring.

The abruptness and timing of the steadily increasing sAOD from January to July 1965 suggests this variation was from a different source than Agung, possibly from one or both of the two VEI3 eruptions that occurred in 1964/65: Trident, Alaska and Vestmannaeyjar, Heimey, south of Iceland.

A detailed error analysis of the uncertainties in each of the variables involved in the processing chain was conducted, relative errors of 54 % for Fairbanks and 44 % Lexington for the uncorrected sAEP532, corrected sAEP532 of 61 % and 64 % respectively.

The analysis of the uncertainties identified variables that, with additional data recovery and reprocessing could reduce these relative error levels. Data described in this work are available at (Dataset in Review) (Antuña-Marrero et al., 2020).

How to cite: Antuña-Marrero, J. C., Mann, G. W., Barnes, J., Rodríguez-Vega, A., Shallcross, S., Dhomse, S., Fiocco, G., and Grams, G. W.: Data rescue of stratospheric aerosol observations from lidar at Lexington, MA, and Fairbanks, AK, January 1964 to July 1965., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14351,, 2021.

Chairpersons: Claudia Timmreck, Matthew Toohey
Non-sulphate/non-volcanic aerosol
Florent Tencé, Julien Jumelet, Alain Sarkissian, Slimane Bekki, and Sergey Khaykin

Australia experienced an unprecedented fire season from August 2019 to March 2020, now colloquially named as Black Summer. As a warming climate could tend to enhance wildfire seasons, it is critical to study their impact on a large scale : pyrocumunolimbus (pyroCb) events directly inject large quantities of material into the stratosphere, from which aerosols can then be transported due to the general circulation patterns. Stratospheric aerosols have an important impact on the radiative budget of the Earth : directly, through the change in albedo they imply, and indirectly, enhancing nucleation processes.

The pyrocumunolimbus events triggered by these wildfires between 2019/12/29 and 2020/01/04 raised the stratospheric aerosol load of the Southern Hemisphere to a rarely observed level and we hereby present the optical signatures and characterization of the smoke-related aerosols detected at the French Antarctic station Dumont d’Urville (66.6°S – 140°E) since their first detection in november 2019 and their presence throughout the 2020 year after long range transport. Combined with satellite measurements from OMI and OMPS, lidar measurements allow us to follow the time evolution of these aerosol layers, their vertical distribution in altitude as well as their optical properties and assessment of the lidar ratio. As the groundbased instrumental coverage remains sparse in the Southern Hemisphere and especially in Antarctica, such events highlight the importance of running monitoring programs at high latitudes.

How to cite: Tencé, F., Jumelet, J., Sarkissian, A., Bekki, S., and Khaykin, S.: Optical properties of smoke particules from Australian 2019-20 wildfires derived from lidar measurements at the French Antarctic station Dumont d’Urville, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12466,, 2021.

Yaowei Li, John Dykema, and Frank Keutsch

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.

How to cite: Li, Y., Dykema, J., and Keutsch, F.: Composition Dependence of Stratospheric Aerosol Radiative Forcing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13162,, 2021.

Graham Mann, James Brooke, Kamalika Sengupta, Lauren Marshall, Sandip Dhomse, Wuhu Feng, Ken Carslaw, Charles Bardeen, Nicolas Bellouin, Mohit Dalvi, Colin Johnson, Luke Abraham, Samuel Remy, Vincent Huijnen, Simon Chabrillat, Zak Kipling, Terry Deshler, and Larry Thomason

The widespread presence of meteoric smoke particles (MSPs) within a distinct class of stratospheric aerosol particles has become clear from in-situ measurements in the Arctic, Antarctic and at mid-latitudes.
We apply an adapted version of the interactive stratosphere aerosol configuration of the composition-climate model UM-UKCA, to predict the global distribution of meteoric-sulphuric particles nucleated heterogeneously on MSP cores. We compare the UM-UKCA results to new MSP-sulphuric simulations with the European stratosphere-troposphere chemistry-aerosol modelling system IFS-CB05-BASCOE-GLOMAP.

The simulations show a strong seasonal cycle in meteoric-sulphuric particle abundance results from the winter-time source of MSPs transported down into the stratosphere in the polar vortex. Coagulation during downward transport sees high latitude MSP concentrations reduce from ~500 per cm3 at 40km to ~20 per cm3 at 25km, the uppermost extent of the stratospheric aerosol particle layer (the Junge layer).
Once within the Junge layer's supersaturated environment, meteoric-sulphuric particles form readily on the MSP cores, growing to 50-70nm dry-diameter (Dp) at 20-25km. Further inter-particle coagulation between these non-volatile particles reduces their number to 1-5 per cc at 15-20km, particle sizes there larger, at Dp ~100nm.

The model predicts meteoric-sulphurics in high-latitude winter comprise >90% of Dp>10nm particles above 25km, reducing to ~40% at 20km, and ~10% at 15km.
These non-volatile particle fractions are slightly less than measured from high-altitude aircraft in the lowermost Arctic stratosphere (Curtius et al., 2005; Weigel et al., 2014), and consistent with mid-latitude aircraft measurements of lower stratospheric aerosol composition (Murphy et al., 1998), total particle concentrations  also matching in-situ balloon measurements from Wyoming (Campbell and Deshler, 2014).
The MSP-sulphuric interactions also improve agreement with SAGE-II observed stratospheric aerosol extinction in the quiescent 1998-2002 period. 
Simulations with a factor-8-elevated MSP input form more Dp>10nm meteoric-sulphurics, but the increased number sees fewer growing to Dp ~100nm, the increased MSPs reducing the stratospheric aerosol layer’s light extinction.

How to cite: Mann, G., Brooke, J., Sengupta, K., Marshall, L., Dhomse, S., Feng, W., Carslaw, K., Bardeen, C., Bellouin, N., Dalvi, M., Johnson, C., Abraham, L., Remy, S., Huijnen, V., Chabrillat, S., Kipling, Z., Deshler, T., and Thomason, L.: The prevalence of meteoric-sulphuric particles within the stratospheric aerosol layer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15390,, 2021.

Juhi Nagori, Narcisa Nechita-Bândă, Masumi Shinkai, Sebastian Danielache, Thomas Röckmann, and Maarten Krol

It is debated how much stratospheric sulfate aerosol (SSA) in volcanically quiescent times is replenished by carbonyl sulfide (COS) oxidation products. The atmospheric COS budget is also currently uncertain, with missing sources and sinks. Isotopic analysis can be used to allocate the missing sources of COS and also to further constrain the relevance of COS to SSA. The measured tropospheric isotopic signature of COS (δ34S) ranges from 10-14 ‰ (Kamezaki et al., 2019; Angert et al.,2019; Hattori et al., 2020; Davidson et al., 2020), whereas SSA δ34S is constrained by only one single measurement at 18 km of 2.6 ‰ (Castleman, 1974). We use an atmospheric column model to constrain the COS isotopic budget and understand the contribution of COS to sulfate. We find that the COS tropospheric signal is determined by the signatures of its precursors (carbon disulfide, CS2, and dimethyl sulfide, DMS) and fractionation during plant uptake and oxidation. Photolysis of COS is important in the stratosphere; the isotopic signal of COS propagates through sulfur dioxide (SO2) to sulfate in the stratosphere. The model can reproduce δ34S between 1-5 ‰ in the lower stratosphere, which encapsulates the observations from Castleman (1974).


  • Angert, A., Said-Ahmad, W., Davidson, C., & Amrani, A. (2019). Sulfur isotopes ratio of atmospheric carbonyl sulfide constrains its sources. Scientific reports, 9(1), 1-8.
  • Castleman Jr, A. W., Munkelwitz, H. R., & Manowitz, B. (1974). Isotopic studies of the sulfur component of the stratospheric aerosol layer. Tellus, 26(1-2), 222-234.
  • Davidson, C., Amrani, A., & Angert, A. (2020). Tropospheric carbonyl sulfide mass-balance based on direct measurements of sulfur isotopes.
  • Hattori, S., Kamezaki, K., & Yoshida, N. (2020). Constraining the atmospheric OCS budget from sulfur isotopes. Proceedings of the National Academy of Sciences, 117(34), 20447-20452.
  • Kamezaki, K., Hattori, S., Bahlmann, E., & Yoshida, N. (2019). Large-volume air sample system for measuring 34S∕ 32S isotope ratio of carbonyl sulfide. Atmospheric Measurement Techniques, 12(2), 1141-1154

How to cite: Nagori, J., Nechita-Bândă, N., Shinkai, M., Danielache, S., Röckmann, T., and Krol, M.: Modelling the tropospheric and stratospheric sulfur isotopes in a column model for volcanically quiescent periods, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14316,, 2021.

Kamalika Sengupta, Graham Mann, Ralf Weigel, James Brooke, Sandip Dhomse, Stephan Borrmann, and John Plane

Meteoric smoke particles (MSPs) provide a steady source of condensation nuclei to the Arctic lower stratosphere, with heterogeneous nucleation to sulphuric acid aerosol particles.  Internally mixed meteoric-sulphuric particles likely also play a significant role in the formation of polar stratospheric clouds and thereby influence stratospheric ozone depletion chemistry, particularly in the quiescent stratosphere.

In several Arctic winter field campaigns (EUPLEX 2002/3, RECONCILE 2009/10, ESSenCe 2010/11),  in-situ stratospheric aerosol particle concentrations measurements were made from the high-altitude Geophysica aircraft, the COPAS instrument measuring total and refractory (non-volatile) particle concentrations at 20 km altitude (see Curtius et al., 2003; Weigel et al., 2014).  

These measurements are consistent with there being a substantial seasonal source of meteoric-sulphuric particles to the lower Arctic stratosphere, from each year’s influx of MSPs  within the winter-time Arctic polar vortex. In this study we investigate the effect of MSPs on the quiescent Junge layer particle concentration as the polar vortex builds up and after it dissipates. 

We use the nudged configuration of the UM-UKCA stratosphere-troposphere composition-climate model to reproduce the vertical profile of stratospheric particles measured in-situ during the COPAS 2003 campaign. Our model simulates two types of stratospheric aerosol particles - pure sulphuric acid particles and sulphuric acid particles with a MSP-core. We show that the model is able to reproduce the vertical profile of aerosol particles observed during the COPAS measurements in winter 2003.

Our findings illustrate the influx of MSP and SO2 from higher altitudes through the polar vortex, the winter-time build-up of SO2 triggering homogeneous nucleation of pure sulphuric particles, also with the seasonal source of MSP-core sulphuric particles nucleated heterogeneously. We assess the effects of MSPs on the quiescent period particle concentration in the Arctic during winter through to spring.

How to cite: Sengupta, K., Mann, G., Weigel, R., Brooke, J., Dhomse, S., Borrmann, S., and Plane, J.: Modelling the progression in the mix of particles within the Arctic stratospheric aerosol layer, including the seasonal source of meteoric smoke particles from the Arctic winter polar vortex , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16540,, 2021.

Sarah Shallcross, Graham Mann, Anja Schmidt, Jim Haywood, Frances Beckett, Anthony Jones, Ryan Neely, Geraint Vaughan, and Sandip Dhomse

Volcanic aerosol simulations with interactive stratospheric aerosol models mostly neglect ash particles, due to a general assumption they sediment out of the volcanic plume within the first few weeks and have limited impacts on the progression of the volcanic aerosol cloud (Niemeier et al., 2009). 

However, observations, such as ground-based and airborne lidar (Vaughan et al., 1994; Browell et al., 1993), along with impactor measurements (Pueschel et al., 1994) in the months after the Mount Pinatubo eruption suggest the base of the aerosol cloud contained ash particles coated in sulphuric acid for around 9 months after the eruption occurred.  Impactor measurements from flights following the 1963 Agung and 1982 El Chichon eruptions also show ash remained present for many months after the eruption (Mossop, 1964; Gooding et al., 1983). 

More recently, satellite, in situ and optical particle counter measurements after the 2014 Mount Kelud eruption showed ash particles ~0.3 µm in size accounting for 20-28% of the volcanic cloud AOD 3 months following the eruption (Vernier et al., 2016; Deshler, 2016).  This evidence suggests that sub-micron ash particles may persist for longer in the atmosphere than is often assumed. 

We explore how the presence of these sub-micron ash particles affects the progression of a major tropical volcanic aerosol cloud, showing results from simulations with a new configuration of the composition-climate model UM-UKCA, adapted to co-emit fine-ash alongside SO2.   In the UM-UKCA simulations, internally mixed ash-sulphuric particles are transported within the existing coarse-insoluble mode of the GLOMAP-mode aerosol scheme.

Size fractions of 0.1, 0.316 and 1 µm diameter ash were tested for the 1991 Mount Pinatubo eruption with an ultra-fine ash mass co-emission of 0.05 and 0.5 Tg, based on 0.1% and 1% of an assumed fine ash emission of 50Tg.  Whereas the 0.316 and 1 µm sized particles sedimented out of the stratosphere within the first 90 days after the eruption, the 0.1 µm persisted within the lower portion of volcanic cloud for ~9 months,  retaining over half its original mass (0.035 Tg) February 1992. 

We investigate model experiments with different injection heights for the co-emitted SO2 and ash, analysing the vertical profile of the ultra-fine ash compared to the sulphate aerosol, and explore the effects on the volcanic aerosol cloud in terms of its overall optical depth and vertical profile of extinction.

The analysis demonstrates that although fine-ash is more persistent than previous modelling studies suggest, these particles have only modest impacts with the radiative heating effect the dominant pathway, with the sub-micron particles not scavenging sufficiently.  

Future work will explore simulations with a further adapted UM-UKCA model with an additional “super-coarse” insoluble mode resolving the super-micron ash, then both components of the fine-ash resolved to test the magnitude of sulfate scavenging effect. 

How to cite: Shallcross, S., Mann, G., Schmidt, A., Haywood, J., Beckett, F., Jones, A., Neely, R., Vaughan, G., and Dhomse, S.: Long-lived ultra-fine ash particles within the Pinatubo volcanic aerosol cloud and their potential impact on its global dispersion and radiative forcings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16034,, 2021.

Ulrike Niemeier, Felix Riede, and Claudia Timmreck

The large explosive eruption of the Laacher See volcano c. 12,900 yrs BP marked the end of explosive volcanism in the East Eifel volcanic zone (Germany). We have reviewed the current evidence for the impact of the Laacher See Eruption (LSE) on the immediate and wider environment as recorded in a range of proxies with a series of interactive stratospheric aerosol model experiments. Recent studies about the climate impact of NH extratropical eruptions and new insights about the dating of the LSE warrant a return to this cataclysmic eruption and its potential influence on Northern Hemisphere climate. Rather detailed reconstructions of its eruption dynamics have been proposed. The eruption might have lasted several weeks or even months, most likely with an initial (~10h) intense early phase resulting in deposits over north-east Germany and the Baltic Sea, and a slightly later and weaker phase leaving deposits south of the volcano towards the Alps.

Our interactive stratospheric aerosol model experiments are based on a reference LSE experiment with emission estimates of 20 Tg of sulfur dioxide (SO2) and 200 Tg of fine-ash, across two eruptive phases in May and June. Additional sensitivity experiments reflect the estimated range of uncertainty of the injection rate and altitude and, assess how the solar-absorptive heating from the 150 Tg of sub-micron ash emitted in the first eruptive phase changed the LSE cloud’s dispersion. Our simulations reveal that the heating of the ash likely played an important role in the transport of ash and sulfate. Depending on the altitude of the injection, our simulated volcanic cloud begins to rotate shortly after the eruption. This meso-cyclone, as well as the additional radiative heating of the fine ash then changes the dispersion of the cloud to be more southerly compared to dispersal estimated without fine-ash heating. Sulfate transport is similarly impacted by the heating of the ash, resulting in a stronger transport to low-latitudes, later arrival of the volcanic cloud in the Arctic regions and a longer lifetime compared to cases without injection of fine ash.

How to cite: Niemeier, U., Riede, F., and Timmreck, C.: Simulation of ash clouds after a Laacher See-type eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2314,, 2021.

Raikoke eruption and post-2010 variations in the stratospheric aerosol layer
Andreas Petzold, Ulrich Bundke, Marcel Berg, Rita Gomes, Jim Haywood, Martin Osborne, Johannes Schneider, Christiane Schulz, Markus Hermann, Florian Obersteiner, Torsten Gehrlein, Harald Boehnisch, Andreas Zahn, and Jean-Paul Vernier

IAGOS (In-Service Aircraft for a Global Observing System; is a European Research Infrastructure which uses passenger aircraft equipped with autonomous instrumentation for the continuous and global-scale observation of atmospheric composition in the upper troposphere and lowermost stratosphere (UT/LS; see Petzold et al., 2015). Among others, IAGOS provides today detailed information on atmospheric trace species by the flying laboratory in IAGOS-CARIBIC. Since July 2018, number concentration and fraction of non-volatile particles for dp > 15 nm as well as size distributions for dp >  250 nm are measured (Bundke et al., 2015). Since lately, aerosol chemical composition is provided as well (Schulz et al., 2020). IAGOS-CARIBIC flight routes covered during the period from July 2018 to March 2020 include regular flights from Munich, Germany, to North America, East Asia and South Africa.

On 22 June 2019, the Raikoke Volcano on the Kuril Islands erupted and transported vast amounts of gaseous and particulate matter into the UT/LS. Two months after the eruption CALIPSO observed enhanced aerosol optical depth and aerosol scattering across the entire lower stratosphere. IAGOS-CARIBIC conducted several flight series in the Northern Hemisphere before and after the eruption phase such that the pre- and post-eruption data provide profound information on the impact of the Raikoke eruption on the Northern Hemisphere UT/LS aerosol and the evolution of the plume during 9 months of regular observation.

Data indicate an increase in the number concentration of particles with dp > 250 nm by a factor of 10 across the entire sampled altitude range, while the increase of the total aerosol number concentration (dp > 15 nm) is less pronounced but also significant. We present a detailed analysis of the changes in UT/LS aerosol load and properties caused by the Raikoke eruption, including the temporal evolution of the aerosol plume during 9 months past the eruption. In-situ observations are backed-up by CALIPSO products and results from associated volcanic plume modelling studies deploying the UK Earth System Model UKESM1.

The authors gratefully acknowledge the continuous support of IAGOS by Deutsche Lufthansa. Without their commitment these observations would not have been possible. Parts of this study were funded by the German Ministry for Education and Research (BMBF) under Grant No. 01LK1301A as part of the joint research programme IAGOS Germany.

Bundke, U., et al. (2015) Tellus B 67, 28339

Petzold, A., et al. (2015) Tellus B 67, 28452

Schulz, C., et al. (2020) EAC 2020 Abstract ID 1258

How to cite: Petzold, A., Bundke, U., Berg, M., Gomes, R., Haywood, J., Osborne, M., Schneider, J., Schulz, C., Hermann, M., Obersteiner, F., Gehrlein, T., Boehnisch, H., Zahn, A., and Vernier, J.-P.: Evolution of the Raikoke volcanic plume in the Northern Hemisphere UT/LS over 9 months past eruption as seen from IAGOS-CARIBIC in-situ observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12781,, 2021.

Mariam Tidiga, Gwenaël Berthet, Fabrice Jegou, Adriana Bossolasco, Corinna Kloss, Nelson Bègue, Jean-Baptiste Renard, Jean-Paul Vernier, Lieven Clarisse, Ghassan Taha, Thierry Portafaix, Jean-Marc Metzger, and Guillaume Payen

The cumulative impacts of frequent moderate-magnitude eruptions on stratospheric aerosols were identified among the factors in recent decadal climate trends. Moderate volcanic eruptions are a recurrent source of sulfur dioxide (SO2) in the Upper Troposphere and Lower Stratosphere (UTLS) region and the resulting formation of sulfuric acid aerosol particles from the SO2 emitted provides sites for chemical reactions leading to enhancement of stratospheric optical depth (SAOD) and ozone depletion. Modelling properly the volcanic aerosol content and its evolution in this region is important for radiative impact issues. In this work, we explore the variability of the tropical UTLS aerosol content between 2013 and 2019, a period which was particularly impacted by moderate tropical and mid-latitude volcanic eruptions. For that purpose, space-borne observations from OMPS (version 2, datasets from GES DISC), and IASI, together with simulations by the Whole Atmosphere Community Climate Model (WACCM) coupled with the Community Aerosol and Radiation Model for Atmospheres (CARMA), are used. Different model sensitive experiments, particularly for the injection altitude and timing, have been conducted to evaluate how the model captures the aerosol plume in terms of content, optical and microphysical properties, transport and residence time. We find that the decay of the Calbuco and Kelud plumes observed by OMPS version 2 is well reproduced by the model. Comparisons with unique datasets in the tropical southern hemisphere from the NDACC Maïdo observatory (Reunion Island, France, 20.5°S, 55.5°E) show good agreement between the lidar SAOD observations and WACCM-CARMA SAOD simulations although we observe a difference in the altitude of the maximum aerosol concentration between the model and the in situ profile after Calbuco eruption in April 2015. A particular focus is also made on recent eruptions like Raikoke, Ambae and Ulawun. The plume of the Ambae volcano (15°S, 167°E) which erupted in July 2018 is shown to propagate to the northern hemisphere with some influence until summer 2019 in the Asian monsoon region. For the year 2019, we investigate how the Ulawun (5°S, 151°E; ~0.14 Tg of SO2) tropical eruption and the Raikoke mid-latitude eruption (48°N, 153°E; ~1.5Tg of SO2), have influenced the aerosol burden in the tropics.

How to cite: Tidiga, M., Berthet, G., Jegou, F., Bossolasco, A., Kloss, C., Bègue, N., Renard, J.-B., Vernier, J.-P., Clarisse, L., Taha, G., Portafaix, T., Metzger, J.-M., and Payen, G.: Variability of the aerosol content in the tropical lower stratosphere from 2013 to 2019 as influenced by moderate volcanic eruptions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2690,, 2021.

Felix Wrana, Christian von Savigny, and Larry W. Thomason

We present surprising results of our stratospheric aerosol size retrieval which is using the SAGE III/ISS solar occultation measurements, that started in 2017. Due to the broad wavelength spectrum covered by the instrument a robust retrieval of the median radius, mode width and number density of monomodal lognormal size distributions is possible.

In the timeframe of SAGE III’s operation so far three small to mid intensity volcanic eruptions that reached and perturbed the stratospheric aerosol layer were observed by the instrument: The Ambae eruptions (15.3°S) in spring of 2018 and the Raikoke (48.3°N) and Ulawun (5.05°S) eruptions, both in June 2019. While the Raikoke eruption led to an increase in the median radius of the stratospheric aerosols, which was to be expected and is in line with previous observations, the Ambae and Ulawun eruption had a different effect. After both eruptions the average aerosol size decreased, with lower median radii and narrower size distributions, while the number density increased strongly. The observation, that volcanic eruptions may lead to smaller average stratospheric aerosol sizes is a novel one and should be of great interest to the modeling as well as remote sensing community.

We will present the temporal and spatial evolution of the stratospheric perturbations and discuss what may distinguish those three eruptions from each other.

How to cite: Wrana, F., von Savigny, C., and Thomason, L. W.: Smaller average stratospheric aerosol sizes after volcanic eruptions in 2018 and 2019, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4309,, 2021.

Nina Mateshvili, Didier Fussen, Iuri Mateshvili, Filip Vanhellemont, Christine Bingen, Tamar Paatashvili, Erkki Kyrölä, Charles Robert, and Emmanuel Dekemper

Twilight sky brightness spectral measurements are an inexpensive and effective way to observe enhancements of stratospheric aerosols. In this work, we present our observations of the volcanic cloud produced by the eruption of Raikoke volcano (Kuril Islands, 48°N, 153°E) above two distinct sites in South Caucasus and Western Europe, respectively: Tbilisi, Georgia (41° 43’ N, 44° 47° E) and Halle, Belgium (50° 44′ N, 4° 14′ E).

We present our dataset, which describes the evolution of the stratospheric aerosol in the period July 2019-December 2020. Stratospheric aerosol vertical extinction profiles were retrieved at 780 nm from spectral measurements of twilight sky brightness above both sites.

The first aerosols originating from Raikoke  were observed in the beginning of July above Halle and in August above Georgia. The layer maximum was mostly observed at 17 km above Georgia and at 10-17 km above Belgium until April-May 2020. Later, the volcanic cloud was observed sporadically until the end of 2020.

How to cite: Mateshvili, N., Fussen, D., Mateshvili, I., Vanhellemont, F., Bingen, C., Paatashvili, T., Kyrölä, E., Robert, C., and Dekemper, E.: Stratospheric aerosol enhancement and decay after Raikoke eruption in July 2019 as observed from Tbilisi, Georgia and Halle, Belgium using ground-based twilight sky brightness spectral measurements., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5223,, 2021.

Zhongyin Cai, Sabine Grießbach, and Lars Hoffmann

Monitoring and modeling of volcanic aerosols is important for understanding the influence of volcanic activity on climate. Here, we applied the Lagrangian transport model Massive-Parallel Trajectory Calculations (MPTRAC) to estimate the total injected SO2 by the stratosphere reaching eruption of the Raikoke volcano (48N, 153E) in June 2019 and its subsequent transport. We used SO2 observations from the AIRS and TROPOMI satellite instruments together with a backward trajectory approach to estimate the altitude-resolved SO2 emission timeseries. Then we applied a scaling factor to the initial estimate of the SO2 mass and added an exponential decay to simulate the time evolution of the total SO2 mass. By comparing the estimated SO2 mass and the observed mass from TROPOMI, we show that the volcano injected 2.1±0.2 Tg SO2 and the e-folding lifetime of the SO2 was about 13~17 days. Further, we compared simulations that were initialized by AIRS and TROPOMI satellite observations with a constant SO2 emission rate. The results show that the model captures the SO2 distributions in the first ~10 days after the eruption. The simulations using AIRS nighttime and TROPOMI measurements show comparable results and model skills which outperform the simulation using a constant emission rate. Our study demonstrates the potential of using combined satellite observations and transport simulations to further improve SO2 time- and height-resolved emission estimates of volcanic eruptions.

How to cite: Cai, Z., Grießbach, S., and Hoffmann, L.: Improved estimation of volcanic SO2 emissions from satellite observations and Lagrangian transport simulations: The 2019 Raikoke eruption case study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9111,, 2021.

Landon Rieger, Adam Bourassa, Daniel Zawada, Doug Degenstein, Sergey Khaykin, and Ghassan Taha

The eruption of Raikoke on June 22nd, 2019 was one of the largest in recent decades, spewing approximately 1.5 Tg of sulfur up to 17 km altitude. This eruption has been widely studied using a combination of climate models and measurement systems, including ground based lidars, in situ particle counters, and a variety of satellite platforms. The early plume has been well categorized by high-resolution measurements from CALIPSO, MODIS, VIIRS, IASI and other nadir viewing instruments, but as the plume ages investigation often shifts to limb sounding instruments that provide greater sensitivity to lower aerosol levels. These instruments have proven critical in understanding the long-term radiative and climatic impacts of stratospheric aerosol burdens after these explosive events, but the complexity of the measurements, sampling, and retrievals has made error characterization in high-loading conditions difficult.

This work explores systematic biases in limb measurements after the Raikoke eruption due to a variety of factors often implicit in the retrievals and analysis. Near-coincident CALIPSO, SAGE III and OMPS-LP measurements are used to investigate saturation of limb-sounding measurement in the early plume. The recent OMPS-LP v2 stratospheric aerosol product is compared with the University of Saskatchewan product to investigate benefits and drawbacks of the tomographic approach. SAGE III measurements are used as a validation when available although coverage limitations preclude comparisons in the thickest parts of the plume.  This work highlights the subtleties in comparing limb observations, with implications for model comparisons after large events such as volcanic eruptions and forest fires. Not only in the early plume, where sampling can be sparse, but also in the weeks and months following the eruption.

How to cite: Rieger, L., Bourassa, A., Zawada, D., Degenstein, D., Khaykin, S., and Taha, G.: Uncertainty in limb aerosol measurements following the Raikoke eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10523,, 2021.

Laura Tomsche, Andreas Marsing, Tina Jurkat-Witschas, Johannes Lucke, Katharina Kaiser, Johannes Schneider, Stephan Borrmann, and Christiane Voigt

Extreme volcanic eruptions inject significant amounts of sulfur-containing species into the lower stratosphere and sustain the stratospheric aerosol layer which tends to cool the atmosphere and surface temperatures.

During the BLUESKY campaign in May/June 2020, the aerosol composition and its precursor gas SO2 were measured with a time-of-flight aerosol mass spectrometer onboard the research aircraft HALO and with a atmospheric chemical ionization mass spectrometer onboard the DLR Falcon. While SO2 was slightly above background levels in the lower stratosphere above Europe, the aerosol mass spectrometer detected an extended aerosol layer. This sulfate aerosol layer was observed on most of the HALO flights and the sulfate mixing ratio increased significantly between 10 and 14 km altitude. Back trajectory calculations show no recent transport of polluted boundary layer air or ground-based emissions into the lower stratosphere. Therefore, we suggest that the stratospheric sulfate aerosol layer might be attributed to the aged stratospheric plume of the volcano Raikoke in Japan. In June 2019, Raikoke injected huge amounts of SO2 into the lower stratosphere, which were converted to sulfate and contributed to the stratospheric aerosol layer. This decaying volcanic aerosol layer was observed with the aerosol mass spectrometer over Europe a year after the eruption. The long-term volcanic remnants enhance the total stratospheric aerosol surface area, facilitate heterogeneous reactions on these particles and provide additional cloud condensation nuclei in the UTLS. They further offset some of the reduced sulfur burden from aviation that was observed during the COVID-19 lockdown in 2020.
The sensitive and highly time resolved airborne measurements of composition and size of stratospheric aerosol from an explosive volcanic eruption help to better constrain sulfur chemistry in the lower stratosphere, validate satellite observations near their detection threshold and can be used to evaluate dispersion and chemistry-climate models on long-term effects of volcanic aerosol. 

How to cite: Tomsche, L., Marsing, A., Jurkat-Witschas, T., Lucke, J., Kaiser, K., Schneider, J., Borrmann, S., and Voigt, C.: Detection of an enhanced stratospheric aerosol layer above Europe one year after the eruption of the volcano Raikoke, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14197,, 2021.

Christoph Brühl, Jennifer Schallock, Jos Lelieveld, Ralf Weigel, Oliver Appel, and Hans Schlager

The chemistry climate model EMAC with interactive stratospheric and tropospheric aerosol is used for transient simulation of aerosol radiative forcing including effects of about 500 explosive volcanic eruptions and desert dust. We demonstrate that volcanic SO2 injections are needed to explain the StratoClim aircraft observations in August 2017 of SO2 and aerosol properties in the UTLS. This presentation includes studies to ISAMIP concerning aerosol optical depth at different wavelengths and contribution of different aerosol types, involving also multi-instrument satellite observations. We demonstrate that sulfate accumulation from consecutive smaller tropical and subtropical eruptions matters for radiative forcing, as for example in 2016.

How to cite: Brühl, C., Schallock, J., Lelieveld, J., Weigel, R., Appel, O., and Schlager, H.: Simulation of aerosol and its radiative effects from 1990 to 2017 by the CCM EMAC as contribution to SSIRC-ISAMIP and StratoClim, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2597,, 2021.

Christina Brodowsky, Timofei Sukhodolov, Aryeh Feinberg, Michael Höpfner, Thomas Peter, Andrea Stenke, and Eugene Rozanov

Volcanic activity is one of the main natural climate forcings and therefore an accurate representation of volcanic aerosols in global climate models is essential. However, direct modelling of sulfur chemistry, sulfate aerosol microphysics and transport is a complex task involving many uncertainties including those related to the volcanic emission magnitude, vertical shape of the plume, and observations of atmospheric sulfur. This study aims to investigate some of these uncertainties and to analyse the performance of the aerosol-chemistry-climate model SOCOL-AERv2 for three medium-sized volcanic eruptions from Kasatochi in 2008, Sarychev in 2009 and Nabro in 2011. In particular, we investigate the impact of different estimates for the initial volcanic plume height and its SO2 content on the stratospheric aerosol burden. The influence of internal model variability and of modelled dynamics is addressed by three free-running simulations and two nudged simulations at different vertical resolutions. Comparing the modelled evolution of the stratospheric aerosol loading and its spread with the Brewer-Dobson-Circulation (BDC) to satellite measurements reveals in general a very good performance of SOCOL-AERv2 during the considered period. However, the large spread in emission estimates logically leads to significant differences in the modelled aerosol burden. This spread results from both the uncertainty in the total emitted mass of sulfur as well as its vertical distribution relative to the tropopause. An additional source of modelled uncertainty is the tropopause height, which varies among the free-running simulations. Furthermore, the validation is complicated by disagreement between different observational datasets. Nudging effects on the tropospheric clouds were found to affect the tropospheric SO2 oxidation paths and the cross-tropopause transport, leading to increased background burdens both in the troposphere and the stratosphere. This effect can be reduced by nudging only horizontal winds but not temperature. A higher vertical resolution of 90 levels (as opposed to 39 in the standard version) increases the stratospheric residence time of sulfate aerosol after low-latitude eruptions by reducing the diffusion speed out of the tropical reservoir. We conclude that the model's uncertainties can be largely defined by both its set-up as by the volcanic emission parameters.

How to cite: Brodowsky, C., Sukhodolov, T., Feinberg, A., Höpfner, M., Peter, T., Stenke, A., and Rozanov, E.: Modelling aspects of the sulfate aerosol evolution after recent volcanic activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16221,, 2021.

Simon Chabrillat, Samuel Remy, Graham Mann, Vincent Huijnen, Zak Kipling, Johannes Flemming, and Richard Engelen

We present interactive stratospheric aerosol simulations with the ICBG system, a  global tropospheric-stratospheric combined aerosol-chemistry model which is an extension to the ECMWF Integrated Forecasting System (IFS), and is developed as part of the Copernicus Atmosphere Monitoring Service (CAMS). ICBG is the result of the merging of two existing CAMS configurations of the IFS:

  • The IFS-GLOMAP tropospheric-stratospheric aerosol microphysics system, which has the GLOMAP-mode aerosol scheme configured for forecast-cycling experiments within the IFS,
  • The IFS-CB05-BASCOE tropospheric (CB05) – stratospheric (BASCOE) chemistry scheme, which is also an established configuration of the IFS within CAMS.

During the first phase of CAMS, the stratospheric chemistry scheme IFS-BASCOE was extended to include the stratospheric sulphur chemistry from the UM-UKCA model, with sulphuric acid production rates from IFS-BASCOE passed each timestep to the aerosol scheme IFS-GLOMAP for aerosol particle nucleation and condensation. The aerosol surface area densities (SAD) simulated by IFS-GLOMAP simulated are similarly passed each timestep to the stratospheric chemistry scheme IFS-BASCOE for  heterogeneous reactions. In a recent progression of this strato-tropospheric modelling system, the climatology for meteoric smoke particles (MSP) used in UM-UKCA has also been implemented. Thus the simulated stratospheric aerosol layer comprises not only pure sulphuric particles nucleated homogeneously but also meteoric-sulphuric particles formed from the MSPs.

We  evaluate the simulated stratosphere aerosol layer in quiescent conditions, comparing it to SAGE-II measurements from the 1998-2002 period. The simulated stratospheric sulfate burden, aerosol extinction, stratospheric aerosol optical depth (sAOD) and surface area density (SAD) agree well with the SAGE-II retrievals. We also show results from ICBG simulations of the volcanic aerosol cloud from a large-magnitude tropical eruption (Pinatubo, June 1991, VEI6) and a medium-magnitude eruption at a northern mid-latitude (Raikoke, June 2019, VEI4).

How to cite: Chabrillat, S., Remy, S., Mann, G., Huijnen, V., Kipling, Z., Flemming, J., and Engelen, R.: Stratospheric chemistry and aerosol modeling in CAMS with the IFS-CB05-BASCOE-GLOMAP (ICBG) system: evaluation in quiescent conditions and in a volcanic eruption., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15138,, 2021.