scholarly journals Co-emission of volcanic sulfur and halogens amplifies volcanic effective radiative forcing

2020 ◽  
Author(s):  
John Staunton-Sykes ◽  
Thomas J. Aubry ◽  
Youngsub M. Shin ◽  
James Weber ◽  
Lauren R. Marshall ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Effective Radius ◽  
Volcanic Aerosol ◽  
Emission Scenarios ◽  
Explosive Volcanic Eruptions ◽  
Stratospheric Cooling ◽  
Global Mean ◽  
Co Emission

Abstract. The evolution of volcanic sulfur and the resulting radiative forcing following explosive volcanic eruptions is well understood. Petrological evidence suggests that significant amounts of halogens may be co-emitted alongside sulfur in some explosive volcanic eruptions, and satellite evidence indicates that detectable amounts of these halogens may reach the stratosphere. In this study, we confront an aerosol-chemistry-climate model with four stratospheric volcanic eruption emission scenarios (56 Tg SO2 ± 15 Tg HCl & 0.086 Tg HBr and 10 Tg SO2 ± 1.5 Tg HCl & 0.0086 Tg HBr) in order to understand how co-emitted halogens may alter the life cycle of volcanic sulfur, stratospheric chemistry and the resulting radiative forcing. The eruption sizes simulated in this work are hypothetical Volcanic Explosivity Index (VEI) 7 (e.g. 1257 Mt. Samalas) and VEI 6 (e.g. 1991 Mt. Pinatubo) eruptions, representing 1 in 500–1000 year and 1 in 50–100 year events respectively, with plausible amounts of co-emitted halogens based on satellite observations and volcanic plume modelling. We show that co-emission of volcanic halogens and sulfur into the stratosphere increases the volcanic ERF by 24–30 % compared to sulfur-only emission. This is caused by an increase in both the forcing from volcanic aerosol-radiation interactions (ERFari) and composition of the stratosphere (ERFclear,clean). Volcanic halogens catalyse the destruction of stratospheric ozone which results in significant stratospheric cooling (1.5–3 K); counteracting the typical stratospheric radiative heating from volcanic sulfate aerosol. The ozone induced stratospheric cooling prevents aerosol self-lofting and keeps the volcanic aerosol lower in the stratosphere with a shorter lifetime, resulting in reduced growth due to condensation and coagulation and smaller peak global-mean effective radius compared to sulfur-only simulations. The smaller effective radius found in both co-emission scenarios is closer to the peak scattering efficiency radius of sulfate aerosol, thus, co-emission of halogens results in larger peak global-mean ERFari (6–8 %). Co-emission of volcanic halogens results in significant stratospheric ozone, methane and water vapour reductions, resulting in significant increases in peak global-mean ERFclear,clean (> 100 %), predominantly due to ozone loss. The dramatic global-mean ozone depletion simulated in both co-emission simulations (22 %, 57 %) would result in very high levels of UV exposure on the Earth's surface, with important implications for society and the biosphere. This work shows for the first time that co-emission of plausible amounts of volcanic halogens can amplify the volcanic ERF in simulations of explosive eruptions; highlighting the need to include volcanic halogens fluxes when simulating the climate impacts of past or future eruptions and providing motivation to better quantify the degassing budgets and stratospheric injection estimates for volcanic eruptions.

scholarly journals Co-emission of volcanic sulfur and halogens amplifies volcanic effective radiative forcing

2021 ◽  
Vol 21 (11) ◽  
pp. 9009-9029
Author(s):  
John Staunton-Sykes ◽  
Thomas J. Aubry ◽  
Youngsub M. Shin ◽  
James Weber ◽  
Lauren R. Marshall ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Effective Radius ◽  
Emission Scenarios ◽  
Effective Radiative Forcing ◽  
Explosive Volcanic Eruptions ◽  
Stratospheric Cooling ◽  
Global Mean ◽  
Co Emission

Abstract. The evolution of volcanic sulfur and the resulting radiative forcing following explosive volcanic eruptions is well understood. Petrological evidence suggests that significant amounts of halogens may be co-emitted alongside sulfur in some explosive volcanic eruptions, and satellite evidence indicates that detectable amounts of these halogens may reach the stratosphere. In this study, we utilise an aerosol–chemistry–climate model to simulate stratospheric volcanic eruption emission scenarios of two sizes, both with and without co-emission of volcanic halogens, in order to understand how co-emitted halogens may alter the life cycle of volcanic sulfur, stratospheric chemistry, and the resulting radiative forcing. We simulate a large (10 Tg of SO2) and very large (56 Tg of SO2) sulfur-only eruption scenario and a corresponding large (10 Tg SO2, 1.5 Tg HCl, 0.0086 Tg HBr) and very large (56 Tg SO2, 15 Tg HCl, 0.086 Tg HBr) co-emission eruption scenario. The eruption scenarios simulated in this work are hypothetical, but they are comparable to Volcanic Explosivity Index (VEI) 6 (e.g. 1991 Mt Pinatubo) and VEI 7 (e.g. 1257 Mt Samalas) eruptions, representing 1-in-50–100-year and 1-in-500–1000-year events, respectively, with plausible amounts of co-emitted halogens based on satellite observations and volcanic plume modelling. We show that co-emission of volcanic halogens and sulfur into the stratosphere increases the volcanic effective radiative forcing (ERF) by 24 % and 30 % in large and very large co-emission scenarios compared to sulfur-only emission. This is caused by an increase in both the forcing from volcanic aerosol–radiation interactions (ERFari) and composition of the stratosphere (ERFclear,clean). Volcanic halogens catalyse the destruction of stratospheric ozone, which results in significant stratospheric cooling, offsetting the aerosol heating simulated in sulfur-only scenarios and resulting in net stratospheric cooling. The ozone-induced stratospheric cooling prevents aerosol self-lofting and keeps the volcanic aerosol lower in the stratosphere with a shorter lifetime. This results in reduced growth by condensation and coagulation and a smaller peak global-mean effective radius compared to sulfur-only simulations. The smaller effective radius found in both co-emission scenarios is closer to the peak scattering efficiency radius of sulfate aerosol, and thus co-emission of halogens results in larger peak global-mean ERFari (6 % and 8 %). Co-emission of volcanic halogens results in significant stratospheric ozone, methane, and water vapour reductions, resulting in significant increases in peak global-mean ERFclear,clean (> 100 %), predominantly due to ozone loss. The dramatic global-mean ozone depletion simulated in large (22 %) and very large (57 %) co-emission scenarios would result in very high levels of UV exposure on the Earth's surface, with important implications for society and the biosphere. This work shows for the first time that co-emission of plausible amounts of volcanic halogens can amplify the volcanic ERF in simulations of explosive eruptions. It highlights the need to include volcanic halogen emissions when simulating the climate impacts of past or future eruptions, as well as the necessity to maintain space-borne observations of stratospheric compounds to better constrain the stratospheric injection estimates of volcanic eruptions.

scholarly journals Model physics and chemistry causing intermodel disagreement within the VolMIP-Tambora Interactive Stratospheric Aerosol ensemble

2021 ◽  
Vol 21 (5) ◽  
pp. 3317-3343
Author(s):  
Margot Clyne ◽  
Jean-Francois Lamarque ◽  
Michael J. Mills ◽  
Myriam Khodri ◽  
William Ball ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Modeling ◽  
Grid Cell ◽  
Stratospheric Aerosol ◽  
Effective Radius ◽  
Volcanic Aerosol ◽  
Aerosol Cloud ◽  
Sulfate Formation ◽  
Physical And Chemical ◽  
Global Mean

Abstract. As part of the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP), several climate modeling centers performed a coordinated pre-study experiment with interactive stratospheric aerosol models simulating the volcanic aerosol cloud from an eruption resembling the 1815 Mt. Tambora eruption (VolMIP-Tambora ISA ensemble). The pre-study provided the ancillary ability to assess intermodel diversity in the radiative forcing for a large stratospheric-injecting equatorial eruption when the volcanic aerosol cloud is simulated interactively. An initial analysis of the VolMIP-Tambora ISA ensemble showed large disparities between models in the stratospheric global mean aerosol optical depth (AOD). In this study, we now show that stratospheric global mean AOD differences among the participating models are primarily due to differences in aerosol size, which we track here by effective radius. We identify specific physical and chemical processes that are missing in some models and/or parameterized differently between models, which are together causing the differences in effective radius. In particular, our analysis indicates that interactively tracking hydroxyl radical (OH) chemistry following a large volcanic injection of sulfur dioxide (SO2) is an important factor in allowing for the timescale for sulfate formation to be properly simulated. In addition, depending on the timescale of sulfate formation, there can be a large difference in effective radius and subsequently AOD that results from whether the SO2 is injected in a single model grid cell near the location of the volcanic eruption, or whether it is injected as a longitudinally averaged band around the Earth.

scholarly journals Model physics and chemistry causing intermodel disagreement within the VolMIP-Tambora Interactive Stratospheric Aerosol ensemble

2020 ◽  
Author(s):  
Margot Clyne ◽  
Jean-Francois Lamarque ◽  
Michael J. Mills ◽  
Myriam Khodri ◽  
William Ball ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Modeling ◽  
Stratospheric Aerosol ◽  
Effective Radius ◽  
Volcanic Aerosol ◽  
Aerosol Cloud ◽  
Intercomparison Project ◽  
Sulfate Formation ◽  
Physical And Chemical ◽  
Global Mean

Abstract. As part of the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP), several climate modeling centers performed a coordinated pre-study experiment with interactive stratospheric aerosol models simulating the volcanic aerosol cloud from an eruption resembling the 1815 Mt Tambora eruption (VolMIP-Tambora ISA ensemble). The pre-study provided the ancillary ability to assess intermodel diversity in the radiative forcing for a large stratospheric-injecting equatorial eruption when the volcanic aerosol cloud is simulated interactively. An initial analysis of the VolMIP-Tambora ISA ensemble showed large disparities between models in the stratospheric global mean aerosol optical depth (AOD). In this study, we now show that stratospheric global mean AOD differences among the participating models are primarily due to differences in aerosol size, which we track here by effective radius. We identify specific physical and chemical processes that are missing in some models and/or parameterized differently between models, which are together causing the differences in effective radius. In particular, our analysis indicates that interactively tracking hydroxyl radical (OH) chemistry following a large volcanic injection of sulfur dioxide (SO2) is an important factor in allowing for the timescale for sulfate formation to be properly simulated. In addition, depending on the timescale of sulfate formation, there can be a large difference in effective radius and subsequently AOD that results from whether the SO2 is injected in a single model gridcell near the location of the volcanic eruption, or whether it is injected as a longitudinally averaged band around the Earth.

Climate forcing and committed global warming: GHGs, aerosols and ozone 1970-2010

2020 ◽  
Author(s):  
Alcide Zhao ◽  
David Stevenson ◽  
Massimi Bollasina
Keyword(s):  
Radiative Forcing ◽  
Daily Precipitation ◽  
Stratospheric Ozone ◽  
Temperature Response ◽  
Climate Impacts ◽  
Climate Projections ◽  
Anthropogenic Aerosols ◽  
Frequency Distributions ◽  
Climate Risks ◽  
Global Mean

<p>It is crucial to reduce uncertainties in our understanding of the climate impacts of short‐lived climate forcers, in the context that their emissions/concentrations are anticipated to decrease significantly in the coming decades worldwide. Using the Community Earth System Model (CESM1), we performed time‐slice experiments to investigate the effective radiative forcing (ERF) and climate respons to 1970–2010 changes in well‐mixed greenhouse gases (GHGs), anthropogenic aerosols, and tropospheric and stratospheric ozone. Once the present‐day climate has fully responded to 1970–2010 changes in all forcings, both the global mean temperature and precipitation responses are twice as large as the transient ones, with wet regions getting wetter and dry regions drier. The temperature response per unit ERF for short‐lived species varies considerably across many factors including forcing agents and the magnitudes and locations of emission changes. This suggests that the ERF should be used carefully to interpret the climate impacts of short‐lived climate forcers. Changes in both the mean and the probability distribution of global mean daily precipitation are driven mainly by GHG increases. However, changes in the frequency distributions of regional mean daily precipitation are more strongly influenced by changes in aerosols, rather than GHGs. This is particularly true over Asia and Europe where aerosol changes have significant impacts on the frequency of heavy‐to‐extreme precipitation. Our results may help guide more reliable near‐future climate projections and allow us to manage climate risks more effectively.</p>

scholarly journals Radiative forcing since preindustrial times due to ozone change in the troposphere and the lower stratosphere

2006 ◽  
Vol 6 (3) ◽  
pp. 575-599 ◽  
Author(s):  
M. Gauss ◽  
G. Myhre ◽  
I. S. A. Isaksen ◽  
V. Grewe ◽  
G. Pitari ◽  
...  
Keyword(s):  
Climate Change ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Climate Models ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Transport Models ◽  
Stratospheric Chemistry ◽  
Ozone Column ◽  
Global Mean

Abstract. Changes in atmospheric ozone have occurred since the preindustrial era as a result of increasing anthropogenic emissions. Within ACCENT, a European Network of Excellence, ozone changes between 1850 and 2000 are assessed for the troposphere and the lower stratosphere (up to 30 km) by a variety of seven chemistry-climate models and three chemical transport models. The modeled ozone changes are taken as input for detailed calculations of radiative forcing. When only changes in chemistry are considered (constant climate) the modeled global-mean tropospheric ozone column increase since preindustrial times ranges from 7.9 DU to 13.8 DU among the ten participating models, while the stratospheric column reduction lies between 14.1 DU and 28.6 DU in the models considering stratospheric chemistry. The resulting radiative forcing is strongly dependent on the location and altitude of the modeled ozone change and varies between 0.25 Wm−2 and 0.45 Wm−2 due to ozone change in the troposphere and −0.123 Wm−2 and +0.066 Wm−2 due to the stratospheric ozone change. Changes in ozone and other greenhouse gases since preindustrial times have altered climate. Six out of the ten participating models have performed an additional calculation taking into account both chemical and climate change. In most models the isolated effect of climate change is an enhancement of the tropospheric ozone column increase, while the stratospheric reduction becomes slightly less severe. In the three climate-chemistry models with detailed tropospheric and stratospheric chemistry the inclusion of climate change increases the resulting radiative forcing due to tropospheric ozone change by up to 0.10 Wm−2, while the radiative forcing due to stratospheric ozone change is reduced by up to 0.034 Wm−2. Considering tropospheric and stratospheric change combined, the total ozone column change is negative while the resulting net radiative forcing is positive.

scholarly journals Sensitivity of atmospheric CO<sub>2</sub> and climate to explosive volcanic eruptions

2011 ◽  
Vol 8 (2) ◽  
pp. 2957-3007 ◽  
Author(s):  
T. L. Frölicher ◽  
F. Joos ◽  
C. C. Raible
Keyword(s):  
Global Warming ◽  
Carbon Cycle ◽  
Surface Temperature ◽  
Time Scales ◽  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Atmospheric Co2 ◽  
Dynamical Response ◽  
Steric Sea Level ◽  
Explosive Volcanic Eruptions

Abstract. Impacts of low-latitude, explosive volcanic eruptions on climate and the carbon cycle are quantified by forcing a comprehensive, fully coupled carbon cycle-climate model with pulse-like stratospheric sulfur release. The model represents the radiative and dynamical response of the climate system to volcanic eruptions and simulates a decrease of global and regional atmospheric surface temperature, regionally distinct changes in precipitation, a positive phase of the North Atlantic Oscillation, and a decrease in atmospheric CO2 after volcanic eruptions. The volcanic-induced cooling reduces overturning rates in tropical soils, which dominates over reduced litter input due to soil moisture decrease, resulting in higher land carbon inventories for several decades. The perturbation in the ocean carbon inventory changes sign from an initially weak carbon sink to a carbon source. Positive carbon and negative temperature anomalies in subsurface waters last up to several decades. The multi-decadal decrease in atmospheric CO2 yields an additional radiative forcing that amplifies the cooling and perturbs the Earth System on much longer time scales than the atmospheric residence time of volcanic aerosols. In addition, century-scale global warming simulations with and without volcanic eruptions over the historical period show that the ocean integrates volcanic radiative cooling and responds for different physical and biogeochemical parameters such as steric sea level or dissolved oxygen. Results from a suite of sensitivity simulations with different amounts of sulfur released and from global warming simulations show that the carbon cycle-climate sensitivity γ, expressed as change in atmospheric CO2 per unit change in global mean surface temperature, depends on the perturbation. On decadal time scales, modeled γ is several times larger for a Pinatubo-like eruption than for the industrial period and for a high emission, 21st century scenario.

scholarly journals Radiative and climate impacts of a large volcanic eruption during stratospheric sulfur geoengineering

2016 ◽  
Vol 16 (1) ◽  
pp. 305-323 ◽  
Author(s):  
A. Laakso ◽  
H. Kokkola ◽  
A.-I. Partanen ◽  
U. Niemeier ◽  
C. Timmreck ◽  
...  
Keyword(s):  
Volcanic Eruption ◽  
Radiative Forcing ◽  
Climate Changes ◽  
Climate Model ◽  
Volcanic Eruptions ◽  
Climate Impacts ◽  
Solar Radiation Management ◽  
Atmospheric Conditions ◽  
Maximum Increase ◽  
Global Mean

Abstract. Both explosive volcanic eruptions, which emit sulfur dioxide into the stratosphere, and stratospheric geoengineering via sulfur injections can potentially cool the climate by increasing the amount of scattering particles in the atmosphere. Here we employ a global aerosol-climate model and an Earth system model to study the radiative and climate changes occurring after an erupting volcano during solar radiation management (SRM). According to our simulations the radiative impacts of the eruption and SRM are not additive and the radiative effects and climate changes occurring after the eruption depend strongly on whether SRM is continued or suspended after the eruption. In the former case, the peak burden of the additional stratospheric sulfate as well as changes in global mean precipitation are fairly similar regardless of whether the eruption takes place in a SRM or non-SRM world. However, the maximum increase in the global mean radiative forcing caused by the eruption is approximately 21 % lower compared to a case when the eruption occurs in an unperturbed atmosphere. In addition, the recovery of the stratospheric sulfur burden and radiative forcing is significantly faster after the eruption, because the eruption during the SRM leads to a smaller number and larger sulfate particles compared to the eruption in a non-SRM world. On the other hand, if SRM is suspended immediately after the eruption, the peak increase in global forcing caused by the eruption is about 32 % lower compared to a corresponding eruption into a clean background atmosphere. In this simulation, only about one-third of the global ensemble-mean cooling occurs after the eruption, compared to that occurring after an eruption under unperturbed atmospheric conditions. Furthermore, the global cooling signal is seen only for the 12 months after the eruption in the former scenario compared to over 40 months in the latter. In terms of global precipitation rate, we obtain a 36 % smaller decrease in the first year after the eruption and again a clearly faster recovery in the concurrent eruption and SRM scenario, which is suspended after the eruption. We also found that an explosive eruption could lead to significantly different regional climate responses depending on whether it takes place during geoengineering or into an unperturbed background atmosphere. Our results imply that observations from previous large eruptions, such as Mount Pinatubo in 1991, are not directly applicable when estimating the potential consequences of a volcanic eruption during stratospheric geoengineering.

Simulation of aerosol and its radiative effects from 1990 to 2017 by the CCM EMAC as contribution to SSIRC-ISAMIP and StratoClim

2021 ◽  
Author(s):  
Christoph Brühl ◽  
Jennifer Schallock ◽  
Jos Lelieveld ◽  
Ralf Weigel ◽  
Oliver Appel ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Volcanic Eruptions ◽  
Aerosol Radiative Forcing ◽  
Desert Dust ◽  
Tropospheric Aerosol ◽  
Aircraft Observations ◽  
Explosive Volcanic Eruptions ◽  
Aerosol Types ◽  
Aerosol Properties

&lt;p&gt;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 SO&lt;sub&gt;2&lt;/sub&gt; injections are needed to explain the StratoClim aircraft observations in August 2017 of SO&lt;sub&gt;2&lt;/sub&gt; 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.&lt;/p&gt;

scholarly journals Radiative forcing since preindustrial times due to ozone change in the troposphere and the lower stratosphere

2005 ◽  
Vol 5 (4) ◽  
pp. 5751-5807 ◽  
Author(s):  
M. Gauss ◽  
G. Myhre ◽  
I. S. A. Isaksen ◽  
W. J. Collins ◽  
F. J. Dentener ◽  
...  
Keyword(s):  
Climate Change ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Climate Models ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Transport Models ◽  
Stratospheric Chemistry ◽  
Ozone Column ◽  
Global Mean

Abstract. Changes in atmospheric ozone have occurred since the preindustrial era as a result of increasing anthropogenic emissions. Within ACCENT, a European Network of Excellence, ozone changes between 1850 and 2000 are assessed for the troposphere and the lower stratosphere (up to 30 km) by a variety of seven chemistry-climate models and three chemical transport models. The modeled ozone changes are taken as input for detailed calculations of radiative forcing. When only changes in chemistry are considered (constant climate) the modeled global-mean tropospheric ozone column increase since preindustrial times ranges from 7.9 DU to 13.8 DU among the ten participating models, while the stratospheric column reduction lies between 14.1 DU and 47.9 DU in the models considering stratospheric chemistry. The resulting radiative forcing is strongly dependent on the location and altitude of the modeled ozone change and varies between 0.26 Wm−2 and 0.53 Wm−2 due to ozone change in the troposphere and −0.25 Wm−2 and +0.12 Wm−2 due to the stratospheric ozone change. Changes in ozone and other greenhouse gases since preindustrial times have altered climate. Six out of the ten participating models have performed an additional calculation taking into account both chemical and climate change. The isolated effect of climate change is an enhancement of the tropospheric ozone column increase in all models, ranging from 1% to 37%, while the stratospheric reduction becomes slightly less severe in most models. In the three climate-chemistry models with detailed tropospheric and stratospheric chemistry the inclusion of climate change increases the resulting radiative forcing due to tropospheric ozone change by up to 0.08 Wm−2, while the radiative forcing due to stratospheric ozone change is reduced by up to 0.14 Wm−2. Considering tropospheric and stratospheric change combined, the total ozone column change is negative while the resulting net radiative forcing is positive.

scholarly journals ENSO sensitivity to radiative forcing

2020 ◽  
Author(s):  
Evgeniya Predybaylo ◽  
Georgiy Stenchikov ◽  
Andrew Wittenberg ◽  
Sergey Osipov
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Southern Oscillation ◽  
Volcanic Eruptions ◽  
Boreal Winter ◽  
Unified Framework ◽  
Surface Cooling ◽  
Radiative Forcings ◽  
Global Mean ◽  
Eruption Magnitude

&lt;p&gt;To improve El Ni&amp;#241;o / Southern Oscillation (ENSO) predictions and projections in a changing climate, it is essential to better understand ENSO&amp;#8217;s sensitivities to external radiative forcings. Strong volcanic eruptions can help to clarify ENSO&amp;#8217;s sensitivities, mechanisms, and feedbacks. Strong explosive volcanic eruptions inject millions of tons of sulfur dioxide into the stratosphere, where they are converted into sulfate aerosols. For equatorial volcanoes, these aerosols can spread globally, scattering and absorbing incoming sunlight, and inducing a global-mean surface cooling. Despite this global-mean cooling effect, paleo data confirm remarkable warming of the eastern equatorial Pacific in the two years after a tropical eruption, with a shift towards an El Ni&amp;#241;o-like state. To illuminate this response and explain why it tends to occur during particular seasons and ENSO phases, we present a unified framework that includes the roles of the seasonal cycle, stochastic wind forcing, eruption magnitude, and various tropical Pacific climate feedbacks. Analyzing over 20,000 years of large-ensemble simulations from the GFDL-CM2.1 climate model forced by volcanic eruptions, we find that the ENSO response comprises both stochastic and deterministic components, which vary depending on the perturbation season and the ocean preconditioning. For boreal winter eruptions, stochastic dispersion largely obscures the deterministic response, being the largest for the strong El Ni&amp;#241;o preconditioning. Deterministic El Ni&amp;#241;o-like responses to summer eruptions are well seen on neutral ENSO and weak to moderate El Ni&amp;#241;o preconditioning and grow with the eruption magnitude. The relative balance of these components determines the predictability and strength of the ENSO response. The results clarify why previous studies obtained seemingly conflicting results.&lt;/p&gt;

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