Current reconstructions of volcanic forcing over the last 2000 years rely on scaling volcanic sulfate measured in ice cores to estimates of stratospheric sulfate burdens and optical properties using relationships derived from the 1991 eruption of Mt. Pinatubo. However, there are large uncertainties associated with these conversions and consequently a large uncertainty in the reconstructions. Here, we explore the relationship between ice sheet sulfate deposition and volcanic forcing in model simulations of the last millennium conducted using the UK Earth System Model with an interactive stratospheric aerosol scheme. Treating the model sulfate deposition timeseries as a measured ice-core record and using established conversions, we explore how many of the large-magnitude volcanic events simulated in the model are missed by looking at deposition alone, and how the volcanic forcing may be overpredicted or underpredicted compared to the model itself. These results will enable us to further explore uncertainty in these relationships, and aid in improving methods to calculate forcing for past eruptions.

How to cite: Marshall, L., Toohey, M., and Schmidt, A.: How much does ice sheet sulfate deposition tell us about volcanic forcing?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14017, https://doi.org/10.5194/egusphere-egu23-14017, 2023.

Sulphate aerosol in the stratosphere recently became an interactive part of many global climate models and its uncertainties are not yet well constrained. Stratospheric sulphate aerosol is modulated by natural emissions of several sulphur-containing species, including volcanic eruptions, as well as anthropogenic emissions. If not directly injected into the stratosphere by large volcanic eruptions, sulphate aerosols and their precursors are transported into the stratosphere via the tropical tropopause. While there have been some model intercomparison activity for the large volcanic eruptions, the background conditions of sulphur species and in particular the stratospheric aerosol layer have thus far not been addressed at all. Evaluating the background conditions in global models allow to identify modelling issues that are usually masked by larger perturbations such as volcanic eruptions, yet may still be of importance after such a perturbation. Some key factors causing differences between models include different microphysical schemes, chemical schemes, as well as transport and cross-tropopause fluxes. In this work, we use 8 models and available observational data to quantify the full background atmospheric sulphur cycle (burdens, fluxes, and their variability) and investigate its uncertainties within the framework of the Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP). We focus on stratospheric aerosol and its transport with the Brewer-Dobson-Circulation, as well as the influence of the polar vortices. We find significant inter-model variations in the background burden of the major sulphur species. Seasonal cycles agree well in the southern hemisphere, whereas the northern hemisphere shows more inter-model differences due to the individual representations of the northern polar vortex.

How to cite: Brodowsky, C., Aquila, V., Bekki, S., Dhomse, S., Laakso, A., Mann, G., Niemeier, U., Quaglia, I., Rozanov, E., Sekiya, T., Tilmes, S., Timmreck, C., Yu, P., Zhu, Y., and Sukhodolov, T.: Evaluating the Uncertainties of the Global Atmospheric Sulphur Budget in a Multi-Model Framework, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14591, https://doi.org/10.5194/egusphere-egu23-14591, 2023.

The Raikoke volcano erupted on 21-22 June 2019 and emitted ~1.5 Tg volcanic ash into the atmosphere. Several previous studies have focused on the large-scale dispersion of volcanic aerosol plumes with space-borne observations and dispersion models. However, height-resolved ground-based observations are still necessary to trace and cross-check the 3-D evolution of aerosol plumes due to their complicated structures. Here, we present a rare ground-based lidar observation of Raikoke aerosol plumes in the mid-latitudes of the Northern Hemisphere (site: Wuhan; location: 30.5°N, 114.4°E) from 25 July to 30 September 2019. Two types of volcanic aerosol plumes were observed, including the main aerosol plume and a single impacted aerosol cloud (referred to as ‘CCC’, or coherent circular clouds). The main aerosol plume first arrived at Wuhan on 25 July and was intermittently observed during the following two months at altitudes of 15.0-20.5 km, with layer-integrated AODs (aerosol optical depths) of 0.001-0.017. From 22 August to 23 September, this aerosol plume underwent two quasi-elliptical transport pathways in East Asia driven by an Asian monsoon anticyclone. The CCC arrived at Wuhan twice at 20.2-21.7 km on 30 July and at 23.2-25.0 km on 24-26 August after self-lofting, corresponding to the former two circles of their transport around the Northern Hemisphere. Both arrivals of the CCC were closely followed by a thin and horizontally extended aerosol plume (named ‘trail’) with a duration of several days. The unique observation location provided us with an opportunity to study the evolution of the vertical distribution and optical properties of volcanic aerosols, which is anticipated to be a crucial supplement/reference for dispersion model simulation, data assimilation, and forecasting refinement.

How to cite: He, Y., Jing, D., and Yin, Z.: Evolution of aerosol plumes from 2019 Raikoke volcanic eruption observed with polarization lidar over central China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13549, https://doi.org/10.5194/egusphere-egu23-13549, 2023.

Large tropical volcanic eruptions can significantly alter stratospheric water vapour either with direct injection or modifying entry pathways and the quantitative magnitude and time evolution of these changes remain uncertain. Using an ensemble volcanic forcing experiment carried out with version 1 of the UK Earth System Model (UKESM1), we explore the changes in the stratospheric water vapour (SWV) by a Pinatubo-like volcanic eruption via modification of the entry pathway. Our simulations show significant increases in SWV three months after the volcanic eruption for the ensemble mean. The increase peaks at 1 ppmv (~17% of the background levels) in the second post-eruption winter and then decays slowly, in accordance with the tropical cold point temperature anomalies. By decomposing the volcanic heating into diabatic aerosol heating and adiabatic dynamical heating, we show that the timing of tropopause heating after the eruption is determined by the seasonal variation of a general decelerated tropical upwelling imposed on the significant direct aerosol heating lasting two years.

How to cite: Zhou, X., Feng, W., Dhomse, S., Mann, G., and Chipperfield, M.: Analysing changes in stratospheric water vapour following Pinatubo-like volcanic eruption using UK Earth System Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15879, https://doi.org/10.5194/egusphere-egu23-15879, 2023.

The 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano caused substantial impacts on the atmosphere, including a large increase of stratospheric aerosol at high altitudes and a massive injection of water vapor.  We show results from application of a two-dimensional tomographic retrieval of aerosol extinction profiles from limb scattered sunlight made by the NASA OMPS Limb Profiler instrument. The tomographic retrieval substantially improves the agreement in magnitude and vertical structure with coincident lidar and occultation observations compared to the standard retrieval. We also show a secondary effect of bias from uncertainty in assumed particle size distribution parameters that results in a systematic underestimation of the aerosol extinction in the altitude region of the peak of the volcanic aerosol layer.

How to cite: Bourassa, A., Zawada, D., Rieger, L., and Degenstein, D.: Tomographic retrievals of Hunga Tonga-Hunga Ha’apai volcanic aerosol, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9208, https://doi.org/10.5194/egusphere-egu23-9208, 2023.

We present instantaneous forcing computed in a transient simulation with the chemistry climate model EMAC considering more than 600 explosive eruptions and plumes of major forest fires observed by limb scanning satellites in the period 1991 to 2021. If not available directly, perturbations of SO₂ in the volcanic plumes, which we use as alternative to the "point source approach", were derived from observed extinctions. For the fires, black and organic carbon is injected at the top of the pyro-cumulonimbus and the resulting increase in extinction is compared with satellite data. Medium sized volcanic eruptions cause a total forcing of up to -0.35W/m² at the top of the atmosphere while for the fires the forcing there can be positive (about 0.2W/m²).

How to cite: Brühl, C., Schallock, J., Lelieveld, J., and Rieger, L.: Radiative forcing by stratospheric aerosol from volcanoes and major fires for the last 3 decades, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3656, https://doi.org/10.5194/egusphere-egu23-3656, 2023.

The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) is a protocol-driven international initiative under the umbrella of the sixth phase of the Coupled Model Intercomparison Project (CMIP6) aiming at coordinating the activities of different Research Institutes involved in numerical climate modelling focused on a multi-model assessment of climate models' performance under strong volcanic forcing conditions. The main objective of the initiative is to assess to what extent responses of the coupled ocean-atmosphere system to the same applied strong volcanic forcing are robustly simulated across state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in their treatment of physical processes. To this purpose, four Tier-1 (mandatory) experiments branched into two main sets, named “volc-pinatubo” and “volc-long” were defined, together with eight more lower-priority experiments. Six years since the definition of the VolMIP protocol (Zanchettin et al., 2016), ensemble simulations of most of the mandatory VolMIP experiments have been completed and made publicly available through the Earth System Grid Federation open platform, with the first VolMIP results being currently published and several analyses in progress. The long turnover time between the experiment design, the integration of the simulations and the analysis of the output motivates an assessment of the overall effectiveness of the VolMIP strategy, particularly in the light of a possible second phase of the initiative.

In this contribution, we will illustrate the status of the initiative, highlight its major achievements and discuss its future perspective in the light of emergent scientific questions regarding volcanically forced climate variability.

Zanchettin, D., Khodri, M., Timmreck, C., Toohey, M., Schmidt, A., Gerber, E. P., Hegerl, G., Robock, A., Pausata, F. S. R., Ball, W. T., Bauer, S. E., Bekki, S., Dhomse, S. S., LeGrande, A. N., Mann, G. W., Marshall, L., Mills, M., Marchand, M., Niemeier, U., Poulain, V., Rozanov, E., Rubino, A., Stenke, A., Tsigaridis, K., and Tummon, F.: The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): experimental design and forcing input data for CMIP6, Geosci. Model Dev., 9, 2701–2719, https://doi.org/10.5194/gmd-9-2701-2016, 2016

How to cite: Zanchettin, D., Timmreck, C., Khodri, M., Hegerl, G., Krüger, K., Pausata, F. S. R., Robock, A., Schmidt, A., and Toohey, M.: The Model Intercomparison Project on the Climatic Response to Volcanic Forcing (VolMIP): Status and Future Perspectives of the Initiative, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2604, https://doi.org/10.5194/egusphere-egu23-2604, 2023.

Large explosive volcanic eruptions can have major impacts on global climate, affecting both radiative balance and inducing interannual-to-decadal dynamical alterations of the atmospheric and ocean circulation. 

Despite some discrepancies across studies regarding the response of ENSO to volcanism based on paleoclimate data, the majority of ENSO reconstructions  display an El Niño–like warming in the year of eruption, while none display a significant La Niña–like response, Furthermore, there has been an emerging consensus from the numerous coupled General Circulation Model studies investigating the impact of tropical volcanism on ENSO, with the overwhelming majority displaying an El Niño–like warming occurring in the year following the eruption. However, the mechanisms that trigger a change in the ENSO state following volcanic eruptions are still debated. The center of the argument is understanding how volcanism can affect the trade winds along the equatorial Pacific.

Here, we shed light on the processes that govern the ENSO response to tropical volcanic eruptions through a series of sensitivity experiments with an Earth System Model where a uniform stratospheric volcanic aerosol loading is imposed over different parts of the tropics. Three tropical mechanisms are tested: the “ocean dynamical thermostat” (ODT); the cooling of the Maritime Continent; and the cooling of tropical northern Africa (NAFR). We find that the NAFR mechanism plays the largest role, while the ODT mechanism is absent in our simulations as La Niña-like rather than El-Niño-like conditions develop following a uniform radiative forcing over the equatorial Pacific.

How to cite: Pausata, F. S. R., Zhao, Y., Zanchettin, D., Caballero, R., and Battisti, D.: Revisiting the mechanisms of ENSO response to tropical volcanic eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3638, https://doi.org/10.5194/egusphere-egu23-3638, 2023.

Large explosive volcanic eruptions are a potential source of uncertainty in future climate projections as they cannot be predicted in advance, but eventually will occur, causing short-term climatic impacts on both local and global scale. Still, an open topic is the volcanic impact on tropical climate variability, in particular El Niño Southern Oscillation (ENSO) and tropical precipitation and the combined effect of both. Sufficient large ensembles simulations with the same model and radiative forcing scenario but varying initial conditions have become a great tool in recent years to disentangle forced and internal variability).  Here we use the EVA-ENS ensemble (Azoulay et al., 2021) which consists of 100-member ensembles of the MPI-ESM-LR for idealized equatorial Pinatubo-like eruptions of different eruption strength and an additional 100-member ensemble without forcing. We are in particular interested if there is a linear volcanic signal on tropical precipitation dependent on the eruption strength and when did it emerge from tropical internal variability.

Our results show that for Idealized tropical eruptions global and large hemispheric mean 2m temperature and precipitation anomalies seemed to be scalable with the sulfur emission strength above a certain threshold, except for tropical temperatures for an emission strength > 40 Tg  sulfur (S). 10 Tg S emission, the upper estimate of the 1991 Pinatubo eruption, seems to be a threshold where the signal is discernible from internal variability. We also find that seasonal and ensemble mean pattern correlation of 2m temperature and precipitation anomalies are highly correlated in particular for larger emission strengths in the tropics and strongly modulated by ENSO.  There is an increasing tendency for a warm ENSO increases with eruption strength. Emergence of the volcanic signal appears for smaller eruption strength when looking to ENSO composites.  Emergence of cooling appears on a hemispheric scale, while precipitation response is more localized and mainly confined to the tropics and subtropics.

 References:

Azoulay, A., Schmidt, H., and Timmreck, C.: The Arctic polar vortex response to volcanic forcing of different strengths, J. Geophys. Res., 126, e2020JD034450, doi.org/10.1029/2020JD034450, 2021.

How to cite: Timmreck, C., Olonscheck, D., Ballinger, A., D'Agostino, R., Fang, S.-W., Hegerl, G., and Schurer, A.: Linear precipitation response to increasingly strong volcanic eruptions and its emergence from internal variability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5428, https://doi.org/10.5194/egusphere-egu23-5428, 2023.