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

2018 ◽  
Author(s):  
Claudia Timmreck ◽  
Graham W. Mann ◽  
Valentina Aquila ◽  
Rene Hommel ◽  
Lindsay A. Lee ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Transport Processes ◽  
Aerosol Layer ◽  
Model Intercomparison ◽  
Aerosol Model ◽  
Model Experiments ◽  
Aerosol Forcing ◽  
Intercomparison Project

Abstract. The Stratospheric Sulfur and its Role in Climate (SSiRC) interactive stratospheric aerosol model intercomparison project (ISA-MIP) explores uncertainties in the processes that connect volcanic emission of sulphur gas species and the radiative forcing associated with the resulting enhancement of the stratospheric aerosol layer. The central aim of ISA-MIP is to constrain and improve interactive stratospheric aerosol models and reduce uncertainties in the stratospheric aerosol forcing by comparing results of standardized model experiments with a range of observations. In this paper we present 4 co-ordinated inter-model experiments designed to investigate key processes which influence the formation and temporal development of stratospheric aerosol in different time periods of the observational record. The Background (BG) experiment will focus on microphysics and transport processes under volcanically quiescent conditions, when the stratospheric aerosol is controlled by the transport of aerosols and their precursors from the troposphere to the stratosphere. The Transient Aerosol Record (TAR) experiment will explore the role of small- to moderate-magnitude volcanic eruptions, anthropogenic sulphur emissions and transport processes over the period 1998–2012 and their role in the warming hiatus. Two further experiments will investigate the stratospheric sulphate aerosol evolution after major volcanic eruptions. The Historical Eruptions SO2 Emission Assessment (HErSEA) experiment will focus on the uncertainty in the initial emission of recent large-magnitude volcanic eruptions, while the Pinatubo Emulation in Multiple models (PoEMS) experiment will provide a comprehensive uncertainty analysis of the radiative forcing from the 1991 Mt. Pinatubo eruption.

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

2018 ◽  
Vol 11 (7) ◽  
pp. 2581-2608 ◽  
Author(s):  
Claudia Timmreck ◽  
Graham W. Mann ◽  
Valentina Aquila ◽  
Rene Hommel ◽  
Lindsay A. Lee ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Transport Processes ◽  
Aerosol Layer ◽  
Model Intercomparison ◽  
Aerosol Model ◽  
Model Experiments ◽  
Aerosol Forcing ◽  
Intercomparison Project

Abstract. The Stratospheric Sulfur and its Role in Climate (SSiRC) Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP) explores uncertainties in the processes that connect volcanic emission of sulfur gas species and the radiative forcing associated with the resulting enhancement of the stratospheric aerosol layer. The central aim of ISA-MIP is to constrain and improve interactive stratospheric aerosol models and reduce uncertainties in the stratospheric aerosol forcing by comparing results of standardized model experiments with a range of observations. In this paper we present four co-ordinated inter-model experiments designed to investigate key processes which influence the formation and temporal development of stratospheric aerosol in different time periods of the observational record. The Background (BG) experiment will focus on microphysics and transport processes under volcanically quiescent conditions, when the stratospheric aerosol is controlled by the transport of aerosols and their precursors from the troposphere to the stratosphere. The Transient Aerosol Record (TAR) experiment will explore the role of small- to moderate-magnitude volcanic eruptions, anthropogenic sulfur emissions, and transport processes over the period 1998–2012 and their role in the warming hiatus. Two further experiments will investigate the stratospheric sulfate aerosol evolution after major volcanic eruptions. The Historical Eruptions SO2 Emission Assessment (HErSEA) experiment will focus on the uncertainty in the initial emission of recent large-magnitude volcanic eruptions, while the Pinatubo Emulation in Multiple models (PoEMS) experiment will provide a comprehensive uncertainty analysis of the radiative forcing from the 1991 Mt Pinatubo eruption.

scholarly journals The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): Experimental design and forcing input data

2016 ◽  
Author(s):  
Davide Zanchettin ◽  
Myriam Khodri ◽  
Claudia Timmreck ◽  
Matthew Toohey ◽  
Anja Schmidt ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Initial Conditions ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Model Intercomparison ◽  
Climatic Response ◽  
Volcanic Forcing ◽  
Intercomparison Project

Abstract. The enhancement of the stratospheric aerosol layer by volcanic eruptions induces a complex set of responses causing global and regional climate effects on a broad range of timescales. Uncertainties exist regarding the climatic response to strong volcanic forcing identified in coupled climate simulations that contributed to the fifth phase of the Climate Model Intercomparison Project (CMIP5). In order to better understand the sources of these model diversities, the model intercomparison project on the climate response to volcanic forcing (VolMIP) has defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the CMIP6 protocol. VolMIP provides a common stratospheric aerosol dataset for each experiment to eliminate differences in the applied volcanic forcing, and defines a set of initial conditions to determine how internal climate variability contributes to determining the response. VolMIP will assess to what extent volcanically-forced responses of the coupled ocean-atmosphere system are robustly simulated by state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in the treatment of physical processes. This paper illustrates the design of the idealized volcanic perturbation experiments in the VolMIP protocol and describes the common aerosol forcing input datasets to be used.

scholarly journals The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): experimental design and forcing input data for CMIP6

2016 ◽  
Vol 9 (8) ◽  
pp. 2701-2719 ◽  
Author(s):  
Davide Zanchettin ◽  
Myriam Khodri ◽  
Claudia Timmreck ◽  
Matthew Toohey ◽  
Anja Schmidt ◽  
...  
Keyword(s):  
Input Data ◽  
Initial Conditions ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Model Intercomparison ◽  
Climatic Response ◽  
Data Set ◽  
Volcanic Forcing ◽  
Intercomparison Project

Abstract. The enhancement of the stratospheric aerosol layer by volcanic eruptions induces a complex set of responses causing global and regional climate effects on a broad range of timescales. Uncertainties exist regarding the climatic response to strong volcanic forcing identified in coupled climate simulations that contributed to the fifth phase of the Coupled Model Intercomparison Project (CMIP5). In order to better understand the sources of these model diversities, the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) has defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the CMIP6 protocol. VolMIP provides a common stratospheric aerosol data set for each experiment to minimize differences in the applied volcanic forcing. It defines a set of initial conditions to assess how internal climate variability contributes to determining the response. VolMIP will assess to what extent volcanically forced responses of the coupled ocean–atmosphere system are robustly simulated by state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in the treatment of physical processes. This paper illustrates the design of the idealized volcanic perturbation experiments in the VolMIP protocol and describes the common aerosol forcing input data sets to be used.

scholarly journals A new Geoengineering Model Intercomparison Project (GeoMIP) experiment designed for climate and chemistry models

2014 ◽  
Vol 7 (4) ◽  
pp. 5447-5464 ◽  
Author(s):  
S. Tilmes ◽  
M. J. Mills ◽  
U. Niemeier ◽  
H. Schmidt ◽  
A. Robock ◽  
...  
Keyword(s):  
Model Comparison ◽  
Stratospheric Aerosol ◽  
Atmospheric Composition ◽  
Model Intercomparison ◽  
Data Set ◽  
Aerosol Forcing ◽  
Input Dataset ◽  
Intercomparison Project ◽  
Total Burden ◽  
The Impact

Abstract. A new Geoengineering Model Intercomparison Project (GeoMIP) experiment "G4 specified stratospheric aerosols" (short name: G4SSA) is proposed to investigate the impact of stratospheric aerosol geoengineering on atmospheric composition, climate, and the environment. In contrast to the earlier G4 GeoMIP experiment, which requires an emission of sulphur dioxide (SO2) into the model, a prescribed aerosol forcing file is provided to the community, to be consistently applied to future model experiments between 2020 and 2100. This stratospheric aerosol distribution, with a total burden of about 2 Tg S has been derived using the ECHAM5-HAM microphysical model, based on a continuous annual tropical emission of 8 Tg SO2 year−1. A ramp-up of geoengineering in 2020 and a ramp-down in 2070 over a period of two years are included in the distribution, while a background aerosol burden should be used for the last 3 decades of the experiment. The performance of this experiment using climate and chemistry models in a multi-model comparison framework will allow us to better understand the significance of the impact of geoengineering and the abrupt termination after 50 years on climate and composition of the atmosphere in a changing environment. The zonal and monthly mean stratospheric aerosol input dataset is available at https://www2.acd.ucar.edu/gcm/geomip-g4-specified-stratospheric-aerosol-data-set.

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

2017 ◽  
Vol 17 (18) ◽  
pp. 10937-10953 ◽  
Author(s):  
Bengt G. Martinsson ◽  
Johan Friberg ◽  
Oscar S. Sandvik ◽  
Markus Hermann ◽  
Peter F. J. van Velthoven ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Radiative Forcing ◽  
Chemical Elements ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Pixe Analysis ◽  
Upper Troposphere ◽  
Particulate Sulfur ◽  
Fine Mode

Abstract. This study is based on fine-mode aerosol samples collected in the upper troposphere (UT) and the lowermost stratosphere (LMS) of the Northern Hemisphere extratropics during monthly intercontinental flights at 8.8–12 km altitude of the IAGOS-CARIBIC platform in the time period 1999–2014. The samples were analyzed for a large number of chemical elements using the accelerator-based methods PIXE (particle-induced X-ray emission) and PESA (particle elastic scattering analysis). Here the particulate sulfur concentrations, obtained by PIXE analysis, are investigated. In addition, the satellite-borne lidar aboard CALIPSO is used to study the stratospheric aerosol load. A steep gradient in particulate sulfur concentration extends several kilometers into the LMS, as a result of increasing dilution towards the tropopause of stratospheric, particulate sulfur-rich air. The stratospheric air is diluted with tropospheric air, forming the extratropical transition layer (ExTL). Observed concentrations are related to the distance to the dynamical tropopause. A linear regression methodology handled seasonal variation and impact from volcanism. This was used to convert each data point into stand-alone estimates of a concentration profile and column concentration of particulate sulfur in a 3 km altitude band above the tropopause. We find distinct responses to volcanic eruptions, and that this layer in the LMS has a significant contribution to the stratospheric aerosol optical depth and thus to its radiative forcing. Further, the origin of UT particulate sulfur shows strong seasonal variation. We find that tropospheric sources dominate during the fall as a result of downward transport of the Asian tropopause aerosol layer (ATAL) formed in the Asian monsoon, whereas transport down from the Junge layer is the main source of UT particulate sulfur in the first half of the year. In this latter part of the year, the stratosphere is the clearly dominating source of particulate sulfur in the UT during times of volcanic influence and under background conditions.

scholarly journals Effective radiative forcing and adjustments in CMIP6 models

2020 ◽  
Vol 20 (16) ◽  
pp. 9591-9618 ◽  
Author(s):  
Christopher J. Smith ◽  
Ryan J. Kramer ◽  
Gunnar Myhre ◽  
Kari Alterskjær ◽  
William Collins ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
Radiative Forcing ◽  
Climate Models ◽  
Coupled Model ◽  
Internal Variability ◽  
Cmip5 Models ◽  
Model Intercomparison ◽  
Aerosol Forcing ◽  
Intercomparison Project ◽  
Effective Radiative Forcing

Abstract. The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W m−2, comprised of 1.81 (±0.09) W m−2 from CO2, 1.08 (± 0.21) W m−2 from other well-mixed greenhouse gases, −1.01 (± 0.23) W m−2 from aerosols and −0.09 (±0.13) W m−2 from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported forcings, due to internal variability, is typically within 0.1 W m−2. The majority of the remaining 0.21 W m−2 is likely to be from ozone. In most cases, the largest contributors to the spread in effective radiative forcing (ERF) is from the instantaneous radiative forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from −0.63 to −1.37 W m−2, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming.

Volcanic forcing of climate since 1850 in an interactive aerosol-chemistry-climate model

2021 ◽  
Author(s):  
Thomas Aubry ◽  
Anja Schmidt ◽  
Alix Harrow ◽  
Jeremy Walton ◽  
Jane Mulcahy ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Coupled Model ◽  
Ice Cores ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Model ◽  
Volcanic Forcing

<p>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.</p><p>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.</p>

Interactive Stratospheric Aerosol models response to different sulfur injection amount and altitude distribution during volcanic eruption

2021 ◽  
Author(s):  
Ilaria Quaglia ◽  
Christoph Brühl ◽  
Sandip Dhomse ◽  
Henning Franke ◽  
Anton Laakso ◽  
...  
Keyword(s):  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Climate Modelling ◽  
Aerosol Layer ◽  
Volcanic Aerosol ◽  
Surface Cooling ◽  
Altitude Distribution ◽  
Aerosol Cloud ◽  
Modelling Studies ◽  
Intercomparison Project

<p>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.</p><p>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.</p><p>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.</p><p>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. </p><p>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.</p><p>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.</p>

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

2020 ◽  
Author(s):  
Corinna Kloss ◽  
Pasquale Sellitto ◽  
Bernard Legras ◽  
Jean-Paul Vernier ◽  
Fabrice Jégou ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Orthogonal Polarization ◽  
Transfer Model ◽  
Aerosol Layer ◽  
The Impact ◽  
Aerosol Plume

<p>Using a combination of satellite, ground-based and in-situ observations, and radiative transfer modelling, we quantify the impact of the most recent moderate volcanic eruptions (Ambae, Vanuatu in July 2018; Raikoke, Russia and Ulawun, New Guinea in June 2019) on the global stratospheric aerosol layer and climate.</p><p>For the Ambae volcano (15°S and 167°E), we use the Stratospheric Aerosol and Gas Experiment III (SAGE III), the Ozone Mapping Profiler Suite (OMPS), the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Himawari geostationary satellite observations of the aerosol plume evolution following the Ambae eruption of July 2018. It is shown that the aerosol plume of the main eruption at Ambae in July 2018 was distributed throughout the global stratosphere within the global large-scale circulation (Brewer-Dobson circulation, BDC), to both hemispheres. Ground-based LiDAR observations in Gadanki, India, as well as in-situ Printed Optical Particle Spectrometer (POPS) measurements acquired during the BATAL campaign confirm a widespread perturbation of the stratospheric aerosol layer due to this eruption. Using the UVSPEC radiative transfer model, we also estimate the radiative forcing of this global stratospheric aerosol perturbation. The climate impact is shown to be comparable to that of the well-known and studied recent moderate stratospheric eruptions from Kasatochi (USA, 2008), Sarychev (Russia, 2009) and Nabro (Eritrea, 2011). Top of the atmosphere radiative forcing values between -0.45 and -0.60 W/m<sup>2</sup>, for the Ambae eruption of July 2018, are found.</p><p>In a similar manner the dispersion of the aerosol plume of the Raikoke (48°N and 153°E) and Ulawun (5°S and 151°E) eruptions of June 2019 is analyzed. As both of those eruptions had a stratospheric impact and happened almost simultaneously, it is challenging to completely distinguish both events. Even though the eruptions occurred very recently, first results show that the aerosol plume of the Raikoke eruption resulted in an increase in aerosol extinction values, double as high as compared to that of the Ambae eruption. However, as the eruption occurred on higher latitudes, the main bulk of Raikoke aerosols was transported towards the northern higher latitude’s in the stratosphere within the BDC, as revealed by OMPS, SAGE III and a new detection algorithm for SO<sub>2</sub> and sulfate aerosol using IASI (Infrared Atmospheric Sounder Interferometer). Even though the Raikoke eruption had a larger impact on the stratospheric aerosol layer, both events (the eruptions at Raikoke and Ambae) have to be considered in stratospheric aerosol budget and climate studies.</p>

scholarly journals Recovery of the first ever multi-year lidar dataset of the stratospheric aerosol layer, from Lexington, MA, and Fairbanks, AK, January 1964 to July 1965

2021 ◽  
Vol 13 (9) ◽  
pp. 4407-4423
Author(s):  
Juan-Carlos Antuña-Marrero ◽  
Graham W. Mann ◽  
John Barnes ◽  
Albeht Rodríguez-Vega ◽  
Sarah Shallcross ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Coupled Model ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Large Variability ◽  
Aerosol Model ◽  
Intercomparison Project ◽  
Relative Errors ◽  
The Tropics

Abstract. 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 694 nm attenuated backscatter at Lexington, Massachusetts, between January 1964 and August 1965, with an additional nine 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 (532 nm) stratospheric aerosol extinction profiles (sAEP532) and stratospheric aerosol optical depth (sAOD532) measurements, utilizing a number of contemporary measurements of several different atmospheric variables. Stratospheric soundings of temperature and pressure generate an accurate local molecular backscattering profile, with nearby ozone soundings determining the ozone absorption, which are used to correct for two-way ozone transmittance. Two-way aerosol transmittance corrections are also applied based on nearby observations of total aerosol optical depth (across the troposphere and stratosphere) from sun photometer measurements. We show that accounting for these two-way transmittance effects substantially increases the magnitude of the 1964/1965 stratospheric aerosol layer's optical thickness in the Northern Hemisphere mid-latitudes, then ∼ 50 % larger than represented in the Coupled Model Intercomparison Project 6 (CMIP6) volcanic forcing dataset. Compared to the uncorrected dataset, the combined transmittance correction increases the sAOD532 by up to 66 % for Lexington and up to 27 % for Fairbanks, as well as individual sAEP532 adjustments of similar magnitude. Comparisons with the few contemporary measurements available show better agreement with the corrected two-way transmittance values. Within the January 1964 to August 1965 measurement time span, the corrected Lexington sAOD532 time series is substantially above 0.05 in three distinct periods, October 1964, March 1965, and May–June 1965, whereas the 6 nights the lidar measured in December 1964 and January 1965 had sAOD values of at most ∼ 0.03. The comparison with interactive stratospheric aerosol model simulations of the Agung aerosol cloud shows that, although substantial variation in mid-latitude sAOD532 are expected from the seasonal cycle in the stratospheric circulation, the Agung cloud's dispersion from the tropics would have been at its strongest in winter and weakest in summer. The increasing trend in sAOD from January to July 1965, also considering the large variability, suggests that the observed variations are from a different source than Agung, possibly from one or both of the two eruptions that occurred in 1964/1965 with a Volcanic Explosivity Index (VEI) of 3: Trident, Alaska, and Vestmannaeyjar, Heimaey, south of Iceland. A detailed error analysis of the uncertainties in each of the variables involved in the processing chain was conducted. Relative errors for the uncorrected sAEP532 were 54 % for Fairbanks and 44 % Lexington. For the corrected sAEP532 the errors were 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 https://doi.org/10.1594/PANGAEA.922105 (Antuña-Marrero et al., 2020a).

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