An analysis of multiwavelength stratospheric aerosol extinction coefficient data from the Stratospheric Aerosol and Gas Experiment II and III/ISS instruments by Thomason et al. (2021) demonstrated a coherent relationship between the perturbation in extinction coefficient in an eruption’s main aerosol layer and the wavelength dependence of that perturbation. The relationship was observed to span multiple orders of magnitude in the aerosol extinction coefficient of stratospheric impact of volcanic events. Since that publication, the 2022 eruption by Hunga Tonga-Hunga Ha’apai is noted for several unique features including its intensity and altitude of the aerosol injection. It is also among the largest eruptions since the 1991 eruption by Mt. Pinatubo. In this paper, we show that this eruption fits well into the extinction coefficient/extinction coefficient ratio space found in the previous publication. In addition, while the previous publication was focused on the peak extinction coefficient following the eruption, herein we examine how well the spatial distribution of enhanced aerosol extinction follows the simple relationship between extinction coefficient and extinction coefficient for the by Hunga Tonga-Hunga Ha’apai  eruption and those previously examined.

Thomason, L. W., Kovilakam, M., Schmidt, A., von Savigny, C., Knepp, T., and Rieger, L.: Evidence for the predictability of changes in the stratospheric aerosol size following volcanic eruptions of diverse magnitudes using space-based instruments, Atmos. Chem. Phys., 21, 1143–1158, https://doi.org/10.5194/acp-21-1143-2021, 2021.

How to cite: Thomason, L. and Kovilakam, M.: SAGE II and SAGE III/ISS inference of the optical perturbations caused by volcanic eruptions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4739, https://doi.org/10.5194/egusphere-egu24-4739, 2024.

Volcanic climate impact is strongly correlated with how high its effluents reach in the atmosphere. Volcanic SO₂ injected into the stratosphere can have a residence time of several years, whereas injections in the troposphere only have a residence time of weeks.
We have performed simulations of the 2009 Sarychev eruption with the Community Earth System Model version 2 (CESM2), Whole Atmosphere Community Climate Model version 6 (WACCM6). We have compared the standard model dataset with two high-resolution datasets developed in our group to investigate the importance of utilizing highly vertically and horizontally resolved SO₂ datasets. The default dataset M16 [1] used in WACCM has a vertical resolution of 1 km and is released in one latitude longitude gridbox. Our two high-vertical resolution datasets, S21-3D, and S21-1D, were created from the dataset of Sandvik et al. [2]. These datasets have a vertical resolution of 200 m, spanning from 7.6 to 18.6 km. S21-3D is distributed over several latitudes and longitudes, whereas S21-1D releases all SO₂ in one latitude longitude gridbox to mimic the default dataset in WACCM.

The SO₂ from S21-3D, and S21-1D is injected at a higher altitude than the M16, leading to a longer residence time for both the SO₂ and the formed stratospheric aerosol. The S21-3D dataset has the highest stratospheric SO₂ and SO₄ concentrations of the three simulations and the concentrations peak later than the other two simulations. The results from the S21-1D dataset are similar to those from the S21-3D simulation but with slightly lower concentrations.

The simulated S21-3D AOD agrees with AOD from the space-borne lidar instrument CALIOP. In the simulation with the M16 dataset, the AOD is underestimated by >50%. The volcanic radiative forcing from the Sarychev eruption was 31% lower at the end of 2009 in the simulation with M16 compared to the simulation with S21-3D.

Our results show that the vertical resolution of SO₂ injections substantially impacts the model’s ability to correctly simulate the climate effects of volcanic eruptions, especially if the SO₂ is injected in the vicinity of the tropopause.

Future work will involve simulating a high vertically resolved dataset of SO₂ of other volcanic eruptions since 2006.

References

[1] Mills, M. J., A. Schmidt, R. Easter, S. Solomon, D. E. Kinnison, S. J. Ghan, R. R. III Neely, D. R. Marsh, A. Conley, C. G. Bardeen, et al. (2016), Global volcanic aerosol properties derived from emissions, 1990–2014, using CESM1(WACCM), J. Geophys. Res. Atmos., 121, 2332–2348, doi:10.1002/2015JD024290.

[2] Sandvik, O. S., Friberg, J., Sporre, M. K., and Martinsson, B. G.: Methodology to obtain highly resolved SO₂ vertical profiles for representation of volcanic emissions in climate models, Atmos. Meas. Tech., 14, 7153–7165, https://doi.org/10.5194/amt-14-7153-2021, 2021.

How to cite: Axebrink, E., Friberg, J., and Sporre, M. K.: High-resolution volcanic SO2 emissions in WACCM produce more realistic AODs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3480, https://doi.org/10.5194/egusphere-egu24-3480, 2024.

We used the regional meteorology-chemistry model WRF-Chem with bin’s sulfate aerosol microphysics to study the climate impact of the Hunga volcano eruption on January 15, 2022. We conduct simulations in the 45S-10N latitude band with periodic boundary conditions in longitude and lateral boundary conditions prescribed from ERA-Interim reanalysis that constrain meteorological fields. The spectral nudging of the horizontal wind components in the stratosphere imposes the QBO.

To simulate the Hunga volcano eruption, we injected 150 Mt of water vapor (WV) and 0.45 Mt of SO₂ into the middle stratosphere at 35 km. Because of the relatively high stratospheric temperature at that altitude, about 120 Mt of water was retained in the stratosphere. The volcanic water vapor cloud was cooled by thermal radiation and, therefore, descended to 25 km in about two weeks. Both the simulated mass of the remaining WV and the altitude of the volcanic “water” layer agree with observations. The zonal mean anomaly of volcanic WV mixing ratio averaged over the 30S-10N latitude belt at 25 km exceeded 10 ppmv for two weeks after the eruption. Still, it reduced to 3-4 ppmv in three months. The global water vapor instantaneous LW radiative forcing at the top of the atmosphere (TOA) appears negative, reaching -0.028 W/m2. At the surface, water vapor radiative forcing is two orders of magnitude smaller than at TOA.

Volcanic SO2 was oxidized in 3-4 weeks. Sulfate aerosol's effective radius grows to 0.4 mm a month after the eruption but decreases to 0.2 m in 3-4 months. The instantaneous globally averaged radiative forcing of volcanic sulfate aerosols is about one order of magnitude stronger than TOA’s water vapor forcing, reaching -0.15 W/m2 a month after the eruption at TOA and surface.

Sulfate aerosols absorb SW and LW radiation, warming the stratosphere, but the loss of heat by thermal emission of water vapor cools the stratosphere by 1K. This cooling decreases the outgoing LW flux at TOA and the downward LW flux at the tropopause. As a result, WV's adjusted global LW radiative forcing becomes positive at TOA, reaching 0.04 W/m2 at TOA and the tropopause. The clear-sky SW forcing is not affected by the stratospheric temperature adjustment. A comparison of water vapor radiative forcing calculated using broadband and line-by-line stand-alone radiative transfer models shows that the RRTM broadband model widely used in global and regional models overestimates the WV radiative forcing almost twice.

Thus, we found that sulfate aerosols dominate the radiative forcing generated by the Hunga volcano eruption for at least eight months after the explosion. By then, the sulfate aerosols and WV forcings decreased 3-5 times compared to their pick values. The direct Hunga aerosol radiative forcing is about 30 times smaller than that of the 1991 Pinatubo eruption. The direct WV radiative forcing at the surface is negligibly tiny all the time. It cannot activate the slow ocean feedback and, therefore, cannot cause long-term climate perturbations. However, strong stratospheric cooling, associated changes in stratospheric circulation, and ozone depletion might affect tropospheric climate indirectly.

How to cite: Stenchikov, G., Ukhov, A., and Osipov, S.: Modeling of Instantaneous and Adjusted Radiative Forcing of the 2022 Hunga Volcano Explosion.  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2141, https://doi.org/10.5194/egusphere-egu24-2141, 2024.

Observations and models have indicated a reduction in global mean precipitation during the years following major volcanic eruptions, yet why this occurs has not been rigorously established. Here we apply an energy budget framework to identify the mechanisms behind reduced post-eruption precipitation. Volcanic aerosols alter the atmosphere’s energy balance, with a precipitation (latent heating) response being one pathway that returns the atmosphere towards equilibrium. Using global climate model simulations, we demonstrate that post-eruption precipitation reduction is primarily a consequence of Earth’s surface and troposphere cooling in response to reflection of sunlight by volcanic aerosols. Additionally, these aerosols directly add energy to the atmosphere by absorbing outgoing longwave radiation, which causes much of the precipitation decline in the first post-eruption year. We further identify mechanisms that limit the post-eruption decline, most prominently the influence of a warmer stratosphere. Lastly, we demonstrate that our results are robust across climate models.

How to cite: McGraw, Z. and Polvani, L. M.: How Volcanic Aerosols Globally Inhibit Precipitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6449, https://doi.org/10.5194/egusphere-egu24-6449, 2024.

Typically, climate simulations covering the historical period start in 1850, with the first fifty years used as a baseline to represent a ‘pre-industrial' climate. The period immediately prior to 1850 is however of particular interest, as it had far more volcanic activity than any time during the subsequent historical period, and this is known to have caused large cooling of global temperatures. Exploring the climate of this period could help to better understand early anthropogenic warming, natural climate variability and anticipate the response to large future eruptions.

Here we will: (1) highlight the development of a new instrumental observation-based dataset (GloSAT) for temperature variations across the globe from 1781 to present; (2) discuss an ensemble of historical simulations with UKESM1 which were started in 1750, 100 years earlier than typical. These two sources of evidence will be used to identify the long-lasting impacts of the early 19th century volcanism and disentangle it from the response to other forcings and internal variations. Longer term effects of this period are also explored with significant differences found with historical simulations run using the same model initialised in 1850 lasting well into the 20th century. The implications of this discrepancy and the role of large volcanic eruptions on multi-decadal climate will be discussed. 

How to cite: Schurer, A., Ballinger, A., Dittus, A., Hawkins, E., Cornes, R., Kent, E., Morice, C., Osborn, T., Rumbold, S., and Hegerl, G.: Importance of early 19th century volcanic activity on long-term climate variability., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10774, https://doi.org/10.5194/egusphere-egu24-10774, 2024.

Volcanic eruptions emit large amounts of sulfur dioxide (SO₂), water, and other chemicals into the atmosphere, both in the troposphere and the stratosphere. Most of the SO₂ is converted to sulfate aerosol, which is eventually deposited following long-range transport. The deposits from large eruptions are potentially detectable in ice cores, but there are many cases in which sulfate layers have not been linked to their source volcanoes. As volcanoes can act as significant shocks to the global climate system, we are interested in locating these eruptions in order to increase understanding of the volcanic record. To narrow down the search, we performed 140 simulations of volcanic eruptions using the GISS ModelE Earth system model. We varied the latitude, longitude, Julian day, plume top, plume bottom, and injected SO₂ and H₂O amounts using a Latin hypercube sampling approach, and analyzed correlations between these parameters and sulfate depositions at ice core sites in Antarctica and Greenland. Using machine learning and parameter estimation, we generated probability distributions and maximum likelihood estimates for the parameters given sulfate deposition data, which can predict latitude with some skill. We find that the volcano latitude and SO₂ content are best correlated with sulfate depositions at each pole, while longitude, Julian day, and H₂O have small or insignificant effects. Plume altitude and thickness are important because they determine how much of the SO₂ is injected into the stratosphere, which has implications for sulfur transport and lifetimes.

How to cite: Maas, M., Tsigaridis, K., and Van Lier-Walqui, M.: Combining Earth System Modeling and Machine Learning to Investigate Volcanic Sulfate Deposition in Polar Ice Cores, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4234, https://doi.org/10.5194/egusphere-egu24-4234, 2024.

Following the eruption of Hunga Tonga–Hunga Ha’apai (HTHH) in January 2022, a significant reduction in stratospheric hydrochloric acid (HCl) was observed in the Southern Hemisphere mid-latitudes during the austral winter of 2022. This eruption injected sulfur dioxide and unprecedented amounts of water vapor into the stratosphere. The objective of this study is to comprehensively understand the substantial loss of HCl in the aftermath of HTHH. Satellite measurements from the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE) and Microwave Limb Sounder (MLS), along with data from the global chemistry-climate model Whole Atmosphere Community Climate Model (WACCM), are employed for the analysis. We first compare the modeled 2022 anomalies of HCl and N2O with observations from ACE and MLS, and find noteworthy agreement between the model outputs and the measured data. We then utilize the observed tracer-tracer relations between N2O and HCl to distinguish HCl chemical processing from dynamical transport. The results indicate a significant role of chemical processing in the observed HCl reduction. The chemical changes in HCl derived from ACE and MLS align with the changes calculated from nudged model simulations, where dynamics are fixed to reanalysis. Further delving into the WACCM’s detailed chemistry, we examine individual chlorine gas-phase and heterogeneous reactions. Heterogeneous chemistry emerges as the primary driver for the chemical loss of HCl, with the reaction between HOBr and HCl on sulfate aerosols identified as the dominant loss process.

How to cite: Zhang, J., Wang, P., Kinnison, D., Solomon, S., and Guan, J.: Stratospheric chlorine activation after the unprecedented water-rich Hunga Tonga eruption, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12589, https://doi.org/10.5194/egusphere-egu24-12589, 2024.

The chemistry-climate model EMAC was used to simulate the period 2019 to 2023 with tropospheric meteorology slightly nudged to ERA5 data. Volcanic SO₂ injections were derived from aerosol extinction observations by OSIRIS and OMPS-LP which were also used for evaluation of the simulated aerosol, which includes organic particles from major forest fires that can linger in the lower stratosphere for more than 2 years. Our simulations consider several hundred explosive volcanic eruptions. The simulations of ozone chemistry include enhanced surface area density and fast heterogeneous chlorine activation on organic particles and will be compared with AURA-MLS observations. The effects of the major water vapour injection by the eruption of Hunga Tonga in 2022 on radiative transfer and chemistry were also analysed (as a contribution to SSIRC Hunga Tonga). 
For example, in 2022 the Hunga Tonga eruption increased the depth of the calculated  Antarctic ozone hole by about 12 DU. The Australian bushfire emissions enhanced the aerosol surface area which deepened the 2020 ozone hole by about 7 DU, with the largest changes near the vortex edge. The smoke effect is expected to increase with updated heterogeneous chemistry.
The computed global instantaneous aerosol radiative forcing by Hunga Tonga at the top of the atmosphere was about -0.12 W/m² in 2022. The injected water vapour by Hunga Tonga exerted a radiative forcing of about +0.04 W/m² in the first four months after the eruption. By the end of 2022, it nearly vanished due to dynamical and chemical adjustments. The absorbing aerosol from the Australian and Canadian forest fire emissions changed the stratospheric aerosol forcing from -0.2 W/m² to +0.3 W/m² in January 2020, and in January 2022 the remaining effect was about 0.05 W/m², reducing the negative forcing by the volcanoes. Continued interesting effects of the Hunga Tonga eruptions are expected for 2023, based on results from ongoing simulations.

How to cite: Brühl, C., Lelieveld, J., Rieger, L., and Santee, M.: Radiative forcing and stratospheric ozone changes due to recent volcanic eruptions and major forest fires, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9210, https://doi.org/10.5194/egusphere-egu24-9210, 2024.

The eruption of the Hunga Tonga - Hunga Ha'apai (HTHH) volcano on January 15, 2022 changed the water vapor content of the stratosphere. The eruption injected about 150 Tg of water vapor (H₂O), roughly 10% of the background stratospheric H₂O content, to altitudes above 50 km. Observations with the Aura Microwave Limb Sounder (MLS) detected the transport and distribution of the H2O cloud after the eruption. This provided a great opportunity to compare the simulated transport of the H₂O cloud in the ICON-Seamless model with the MLS observation to see the performance of the stratospheric dynamics in this newly developed model. ICON-Seamless simulations were performed with NWP physics in a low horizontal resolution of about 160 km. A new vertical grid with 130 levels and a maximum grid size of 500 m in the stratosphere allowed the simulation of an internally generated QBO.

The simulated spatial evolution of the H₂O cloud is very close to the MLS observations. In both, model and observation, the vertical transport of the H₂O cloud had three phases: an initial subsidence phase, a stable phase, and a rising phase. Radiative cooling of H₂O clearly affects the transport of the H₂O cloud, as demonstrated with passive tracers. It is the main driver within the subsidence phase. The radiative cooling also counteracts the large-scale rising motion in the tropics, leading to the stable phase, and modulates the large-scale transport of the H₂O cloud for about nine months. This holds for different QBO phases, where the H₂O cloud differs mainly in its vertical extent.

How to cite: Niemeier, U., Wallis, S., Timmreck, C., van Pham, T., and von Savigny, C.: How the Hunga Tonga - Hunga Ha’apai water vapor cloud impacts its transport through the stratosphere: Dynamical and radiative effects, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11045, https://doi.org/10.5194/egusphere-egu24-11045, 2024.

We utilized the Earth System model SOCOLv4 to assess the impacts of the Hunga Tonga-Hunga Ha’apai eruption comprehensively. To accurately estimate the model's performance in terms of water vapour and aerosol plume transport during the initial year, we conducted a multi-member ensemble of free-running simulations and additional simulations employing atmospheric dynamics specified to the ERA5 reanalysis data. These simulations were compared with satellite and reanalysis products. The free-running ensemble simulations with only SO2 (no additional H2O) emissions showed the importance of the two species interaction for the resulting sulphate aerosol evolution, in agreement with previous studies. Furthermore, our primary free-running ensemble simulations, comparing scenarios with and without the eruption event, unravelled a negative response in polar stratospheric ozone levels and temperature. Importantly, these changes were found to be coupled to polar vortex dynamics confirming a larger ozone hole during the austral winter and spring of 2023.

How to cite: Kuchar, A., Sukhodolov, T., Chiodo, G., Rieder, H., Kult-Herdin, J., Stenke, A., and Rozanov, E.: Impacts of the Hunga Tonga-Hunga Ha'apai Eruption: Insights from the SOCOLv4 ESM about past and future, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12714, https://doi.org/10.5194/egusphere-egu24-12714, 2024.

The amount of time that volcanic aerosols spend in the stratosphere is one of the primary factors influencing the climate impact of volcanic eruptions. Descriptions of stratospheric aerosol persistence vary, with many works quoting an approximately 1-year residence time for aerosol from large tropical eruptions, but other references to 1-2 year “lifetimes”. We introduce a framework for describing the evolution of global stratospheric aerosol after major volcanic eruptions and assess its persistence, based on analysis of global satellite-based aerosol observations, tracer transport simulations and simple conceptual modeling. We show that stratospheric residence time, which is estimated through passive tracer pulse experiments and is one factor influencing the lifetime of stratospheric aerosols, is strongly dependent on the injection latitude and height, with an especially strong sensitivity to injection height in the first four kilometers above the tropical tropopause. Time series of simulated stratospheric tracer fraction are best described by a simple model which includes a lag between the injection and initiation of removal from the stratosphere. A simple model including lagged decay, as well as a timescale for sulfate aerosol production, produces a best fit to global observations of stratospheric aerosol after the 1991 eruption of Mt. Pinatubo consistent with a stratospheric lifetime of about 24 months. We estimate the potential impact of observational uncertainties on this lifetime estimate and find it likely that the lifetime of Pinatubo stratospheric aerosol is 20 months or greater. 

How to cite: Toohey, M., Jia, Y., Khanal, S., and Tegtmeier, S.: Stratospheric residence time and the lifetime of volcanic stratospheric aerosols, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13913, https://doi.org/10.5194/egusphere-egu24-13913, 2024.

We present findings from a series of interactive stratospheric aerosol simulations of the Hunga-Tonga volcanic aerosol cloud with the UM-UKCA composition-climate model (Dhomse et al., 2020; Marshall et al., 2019; Dhomse et al., 2014).

The January 2022 Hunga eruption was the most explosive eruption in the satellite era (Wright et al., 2022), an upper portion of the volcanic aerosol plume at 30-40km (Taha et al., 2022), with the main detrainment initially at ~27-30km, a highly unusual steep descent of the plume seeing the aerosol layer form at ~22-26km (e.g. Kloss et al., 2022; Legras et al., 2022; Baron et al., 2023).

The eruption emitted only a modest 0.4-0.5Tg of SO₂ to the stratosphere (Carn et al., 2022).   but generated the strongest stratospheric aerosol optical depth for 30 years (e.g. Khaykin et al., 2022; Taha et al., 2022; Bourassa et al., 2023)

The shallow underwater explosion also detrained ~150Tg of water vapour deep into the stratosphere (e.g. Millan et al., 2022), shown by Zhu et al. (2022) and Asher et al. (2023) to have accelerated SO₂ oxidation and enhanced the growth of volcanic sulphate aerosol, the particles more readily reaching optically-active sizes.

The GLOMAP aerosol module within UM-UKCA model predicts the stratospheric sulphate aerosol particles that form heterogeneously around meteoric smoke particles, alongside the sulphate aerosol that nucleate homogeneously (see Brooke et al., 2017; Dhomse et al. (2020).   The model transports these two sulphate aerosol types in separate modes in the aerosol microphysics module, including with their microphysical interactions (coagulation and uptake of sulphuric acid).

For the major volcanic aerosol clouds in most previous UM-UKCA stratospheric aerosol publications, the meteoric-sulphuric aerosol have only a minor role on volcanic forcing (via modulated decay timescale). Here we explore the significance of the meteoric aerosol within SO₂-only simulations of the Hunga-Tonga volcanic aerosol cloud’s global dispersion.

The long residence times for stratospheric aerosol particles within the tropical stratospheric reservoir means the stratospheric aerosol layer’s column burden enhancement after modest eruptions can be determined not only from the amount of volcanic SO₂ emitted, but partly also reflects the residence time of the mix of stratospheric aerosol particles. 

We explore more generally the role of meteoric-sulphuric particles within moderate SO₂ emission tropical stratosphere-injecting eruptions, exploring the transition from sheared volcanic plume to dispersed aerosol cloud, and how the additional volcanic aerosol particles combine with the two types of sulphuric acid particles in the background aerosol.

The series of UM-UKCA model experiments align with protocols for the Tonga-MIP multi-model experiment (Clyne et al., 2022), and explore how moderate volcanic enhancements to the stratospheric aerosol layer evolve in the transitional post-plume phase across months 2 to 4 after the eruption.

We analyse how the predicted size distributions of the two sulphate aerosol types progress after moderate volcanic eruptions, exploring simulated co-variations of particle size  with multi-wavelength aerosol extinction and sulphate mass. We compare also to satellite measurements after Hunga-Tonga and for other recent moderate stratosphere-injecting eruptions.

How to cite: Mann, G., Dhomse, S., Yoshioka, M., Heddell, S., Hatcher, R., Lister, G., Taha, G., Kovilakam, M., Knepp, T., Thomason, L., and Clyne, M.: Interactive and microphysical simulations of the stratospheric aerosol layer: Global size distribution variation after moderate volcanic enhancement , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19182, https://doi.org/10.5194/egusphere-egu24-19182, 2024.