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The recovery and re-calibration of a dataset of vertical aerosol extinction profiles of the 1963/64 stratospheric aerosol layer measured by a searchlight at 32° N in New Mexico, US, is reported. The recovered dataset consists of 105 aerosol extinction profiles at 550 nm that cover the period from December 1963 to December 1964. It is a unique record of the portion of the aerosol cloud from the March 1963 Agung volcanic eruption that was transported into the Northern Hemisphere subtropics. The data-recovery methodology involved re-digitizing the 105 original aerosol extinction profiles from individual Figures within a research report, followed by the re-calibration. It involves inverting the original equation used to compute the aerosol extinction profile to retrieve the corresponding normalized detector response profile. The re-calibration of the original aerosol extinction profiles used Rayleigh extinction profiles calculated from local soundings. Rayleigh and aerosol slant transmission corrections are applied using the MODTRAN code in transmission mode. Also, a best-estimate aerosol phase function was calculated from observations and applied to the entire column. The tropospheric aerosol phase function from an AERONET station in the vicinity of the searchlight location was applied between 2.76 to 11.7 km. The stratospheric phase function, applied for a 12.2 to 35.2 km altitude range, is calculated from particle-size distributions measured by a high-altitude aircraft in the vicinity of the searchlight in early 1964. The original error estimate was updated considering unaccounted errors. Both the re-calibrated aerosol extinction profiles and the re-calibrated stratospheric aerosol optical depth magnitudes showed higher magnitudes than the original aerosol extinction profiles and the original stratospheric aerosol optical depth, respectively. However, the magnitudes of the re-calibrated variables show a reasonable agreement with other contemporary observations. The re-calibrated stratospheric aerosol optical depth demonstrated its consistency with the tropics-to-pole decreasing trend, associated with the major volcanic eruption stratospheric aerosol pattern when compared to the time-coincident stratospheric aerosol optical depth lidar observations at Lexington at 42° N. [ABSTRACT FROM AUTHOR]

We report the recovery and re-calibration of an extensive dataset of vertical profile measurements of the 1963/64 stratospheric aerosol layer measured from a two-site searchlight measurement facility at White Sands missile base and Sacramento Peak observatory, in New Mexico, US. The recovered dataset comprises 105 profiles of 550nm aerosol extinction (βp(z)) and is part of a longer program of measurements with the US Air Force Cambridge Research Laboratories (AFCRL) searchlight facility that began in February 1963. The recovered series of βp(z) profiles span the 13-month period December 1963 to December 1964 and provide a unique record of the altitude and vertical extent of the Northern Hemisphere dispersed portion of the aerosol cloud from the March 1963 Agung volcanic eruption. The data recovery methodology involved first re-digitizing the 105 original βp(z) profiles (βp(z)) from individual Figures within an AFCRL research report (Elterman, 1966a). The re-calibration involves inverting the original equation used to compute βp(z) in Elterman (1966a; 1966b) to retrieve a normalized detector response (Er(z) Er(35)) profile for each of the 105 re-digitized βp 0(z) profiles. An iterative procedure was then used to compute the re-calibration βp(z) profiles (βp Ra(z)), with the molecular extinction profile calculated with the corresponding daily molecular extinction profile calculated from local soundings, rather than the US Standard Atmosphere 1962 in the original dataset. Two-way molecular and aerosol transmittance corrections are applied using the MODTRAN (MODerate resolution atmospheric TRANsmission) code in transmission mode, applying a best-estimate aerosol phase function calculated from measurements, applied for the entire 2.76 to 35.2 km column. For the tropospheric aerosol transmittance, the AERONET aerosol phase function from White Sands High Energy Laser Systems Test Facility (HELSTF) was applied (2.76 to 10.7 km), a separate stratospheric phase function applied between 11.2 and 35.2 km, calculated from a set of particle size distributions measured by the U-2 high-altitude aircraft over a US region in the vicinity of White Sands in early 1964. Errors were estimated taking as a reference the errors determined in the computation of βp 0(z). Using available tabulated data from the original procedure the errors in the re-digitalization of βp 0(z) and in the retrieval of the Er(z) Er(35) procedures were calculated and later added to the original estimates. Both the βp R(z) and the stratospheric aerosol optical depth magnitudes showed higher magnitudes than βp 0(z) and the original stratospheric aerosol optical depth, however their magnitudes show a reasonable agreement with other contemporary observations. Both the original and recalibration datasets are being submitted to PANGAEA data repository for its storage and public access. [ABSTRACT FROM AUTHOR]

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 (sAEP 532) and stratospheric aerosol optical depth (sAOD 532) 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 sAOD 532 by up to 66 % for Lexington and up to 27 % for Fairbanks, as well as individual sAEP 532 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 sAOD 532 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 sAOD 532 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 sAEP 532 were 54 % for Fairbanks and 44 % Lexington. For the corrected sAEP 532 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 10.1594/PANGAEA.922105 (Antuña-Marrero et al., 2020a). [ABSTRACT FROM AUTHOR]

We report the recovery and processing methodology of the first ever multi-year lidar dataset of the stratospheric aerosol layer. A Q-switched Ruby lidar measured 66 vertical profiles of 694nm attenuated backscatter at Lexington, Massachusetts between January 1964 and August 1965, with an additional 9 profile measurements conducted from College, Alaska during July and August 1964. We describe the processing of the recovered lidar backscattering ratio profiles to produce mid-visible (532nm) stratospheric aerosol extinction profiles (sAEP532) and stratospheric aerosol optical depth (sAOD532) measurements, 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, those profiles then used to correct for two-way ozone transmittance. Two-way aerosol transmittance corrections were also applied based on nearby observations of total aerosol optical depth (across the troposphere and stratosphere) from sun photometer measurements . We show the two-way transmittance correction has substantial effects on the retrieved sAEP532 and sAOD532, calculated without the corrections resulting in substantially lower values of both variables, as it was not applied in the original processing producing the lid ar scattering ratio profiles we rescued. The combined transmittance corrections causes the aerosol extinction to increase by 67 % for Lexington and 27 % for Fairbanks, for sAOD532 the increases 66 % and 26 % respectively. Comparing the magnitudes of the aerosol extinction and sAOD with the few contemporary available measurements reported show a better agreement in the case of the two way transmittance corrected values. The sAEP and sAOD timeseries at Lexington show a surprisingly large degree of variability, three periods where the stratospheric aerosol layer had suddenly elevated optical thickness, the highest sAOD532 of 0.07 measured at the end of March 1965. The two other periods of enhanced sAOD532 are both two-month periods where the lidars show more than 1 night where ret rieved sAOD532 exceeded 0.05: in January and February 1964 and November and December 1964. Interactive stratospheric aerosol model simulations of the 1963 Agung cloud illustrate that although substantial variation in mid-latitude sAOD532 is expected from the seasonal cycle in the Brewer-Dobson circulation, the Agung cloud dispersion will have caused much slower increase than the more episodic variations observed, with also different timing, elevated optical thickness from Agung occurring in winter and spring. The abruptness and timing of the steadily increasing sAOD from January to July 1965 suggests this variation was from a different source than Agung, possibly from one or both of the two VEI3 eruptions that occurred in 1964/65: Trident, Alaska and Vestmannaeyjar, Heimey, south of Iceland. A detailed error analysis of the uncertainties in each of the variables involved in the processing chain was conducted, relative errors of 54 % for Fairbanks and 44 % Lexington for the uncorrected sAEP532, corrected sAEP532 of 61 % and 64 % respectively. The analysis of the uncertainties identified variables that, with additional data recovery and reprocessing could reduce these relative error levels. Data described in this work are available at https://doi.pangaea.de/10.1594/PANGAEA.922105 (Dataset in Review) (Antuña-Marrero et al., 2020a). [ABSTRACT FROM AUTHOR]

Accurately quantifying volcanic impacts on climate is a key requirement for robust attribution of anthropogenic climate change. Here we use the Unified Model – United Kingdom Chemistry and Aerosol (UM-UKCA) composition–climate model to simulate the global dispersion of the volcanic aerosol clouds from the three largest eruptions of the 20th century: 1963 Mt Agung, 1982 El Chichón, and 1991 Mt Pinatubo. The model has interactive stratospheric chemistry and aerosol microphysics, with coupled aerosol–radiation interactions for realistic composition–dynamics feedbacks. Our simulations align with the design of the Interactive Stratospheric Aerosol Model Intercomparison (ISA-MIP) "Historical Eruption SO2 Emissions Assessment". For each eruption, we perform three-member ensemble model experiments for upper, mid-point, and lower estimates of SO2 emission, each re-initialised from a control run to approximately match the observed transition in the phase of the quasi-biennial oscillation (QBO) in the 6 months after the eruptions. With this experimental design, we assess how each eruption's emitted SO2 translates into a tropical reservoir of volcanic aerosol and analyse the subsequent dispersion to mid-latitudes. We compare the simulations to the volcanic forcing datasets (e.g. Space-based Stratospheric Aerosol Climatology (GloSSAC); , and) that are used in historical integrations for the two most recent Coupled Model Intercomparison Project (CMIP) assessments. For Pinatubo and El Chichón, we assess the vertical extent of the simulated volcanic clouds by comparing modelled extinction to the Stratospheric Aerosol and Gas Experiment (SAGE-II) v7.0 satellite measurements and to 1964–1965 Northern Hemisphere ground-based lidar measurements for Agung. As an independent test for the simulated volcanic forcing after Pinatubo, we also compare simulated shortwave (SW) and longwave (LW) top-of-the-atmosphere radiative forcings to the flux anomalies measured by the Earth Radiation Budget Experiment (ERBE) satellite instrument. For the Pinatubo simulations, an injection of 10 to 14 Tg SO2 gives the best match to the High Resolution Infrared Sounder (HIRS) satellite-derived global stratospheric sulfur burden, with good agreement also with SAGE-II mid-visible and near-infra-red extinction measurements. This 10–14 Tg range of emission also generates a heating of the tropical stratosphere that is consistent with the temperature anomaly present in the ERA-Interim reanalysis. For El Chichón, the simulations with 5 and 7 Tg SO2 emission give best agreement with the observations. However, these simulations predict a much deeper volcanic cloud than represented in the GloSSAC dataset, which is largely based on an interpolation between Stratospheric Aerosol Measurements (SAM-II) satellite and aircraft measurements. In contrast, these simulations show much better agreement during the SAGE-II period after October 1984. For 1963 Agung, the 9 Tg simulation compares best to the forcing datasets with the model capturing the lidar-observed signature of the altitude of peak extinction descending from 20 km in 1964 to 16 km in 1965. Overall, our results indicate that the downward adjustment to SO2 emission found to be required by several interactive modelling studies when simulating Pinatubo is also needed when simulating the Agung and El Chichón aerosol clouds. This strengthens the hypothesis that interactive stratospheric aerosol models may be missing an important removal or re-distribution process (e.g. effects of co-emitted ash) which changes how the tropical reservoir of volcanic aerosol evolves in the initial months after an eruption. Our model comparisons also identify potentially important inhomogeneities in the CMIP6 dataset for all three eruption periods that are hard to reconcile with variations predicted in the interactive stratospheric aerosol simulations. We also highlight large differences between the CMIP5 and CMIP6 volcanic aerosol datasets for the Agung and El Chichón periods. Future research should aim to reduce this uncertainty by reconciling the datasets with additional stratospheric aerosol observations. [ABSTRACT FROM AUTHOR]

A key limitation of volcanic forcing datasets for the Pinatubo period is the large uncertainty that remains with respect to the extent of the optical depth of the Pinatubo aerosol cloud in the first year after the eruption, the saturation of the SAGE-II instrument restricting it to only be able to measure the upper part of the aerosol cloud in the tropics. Here we report the recovery of stratospheric aerosol measurements from two shipborne lidars, both of which measured the tropical reservoir of volcanic aerosol produced by the June 1991 Mount Pinatubo eruption. The lidars were on board two Soviet vessels, each ship crossing the Atlantic, their measurement datasets providing unique observational transects of the Pinatubo cloud across the tropics from Europe to the Caribbean (∼ 40 to 8 ∘ N) from July to September 1991 (the Professor Zubov ship) and from Europe to south of the Equator (∼ 40 ∘ N to 8 ∘ S) between January and February 1992 (the Professor Vize ship). Our philosophy with the data recovery is to follow the same algorithms and parameters that appear in the two peer-reviewed articles that presented these datasets in the same issue of GRL in 1993, and here we provide all 48 lidar soundings made from the Professor Zubov and 11 of the 20 conducted from the Professor Vize , ensuring we have reproduced the aerosol backscatter and extinction values in the figures of those two papers. These original approaches used thermodynamic properties from the CIRA-86 standard atmosphere to derive the molecular backscattering, vertically and temporally constant values applied for the aerosol backscatter-to-extinction ratio, and the correction factor of the aerosol backscatter wavelength dependence. We demonstrate this initial validation of the recovered stratospheric aerosol extinction profiles, providing full details of each dataset in this paper's Supplement S1, the original profiles of backscatter ratio, and the calculated profiles of aerosol backscatter and extinction. We anticipate these datasets will provide potentially important new observational case studies for modelling analyses, including a 1-week series of consecutive soundings (in September 1991) at the same location showing the progression of the entrainment of part of the Pinatubo plume into the upper troposphere and the formation of an associated cirrus cloud. The Zubov lidar dataset illustrates how the tropically confined Pinatubo aerosol cloud transformed from a highly heterogeneous vertical structure in August 1991, maximum aerosol extinction values around 19 km for the lower layer and 23–24 for the upper layer, to a more homogeneous and deeper reservoir of volcanic aerosol in September 1991. We encourage modelling groups to consider new analyses of the Pinatubo cloud, comparing the recovered datasets, with the potential to increase our understanding of the evolution of the Pinatubo aerosol cloud and its effects. Data described in this work are available at 10.1594/PANGAEA.912770 (Antuña-Marrero et al., 2020). [ABSTRACT FROM AUTHOR]

A key limitation of volcanic forcing datasets for the Pinatubo period, is the large uncertainty that remains with respect to the extent of the optical depth of the Pinatubo aerosol cloud in the first year after the eruption, the saturation of the SAGE-II instrument restricting it to only be able to measure the upper part of the aerosol cloud in the tropics. Here we report the recovery of stratospheric aerosol measurements from two ship-borne lidars, both of which measured the tropical reservoir of volcanic aerosol produced by the June 1991 Mount Pinatubo eruption. The lidars were on-board two Soviet vessels, each ship crossing the Atlantic, their measurement datasets providing unique observational transects of the Pinatubo cloud across the tropics from Europe to the Caribbean (~ 40° N to 8° N) from July to September 1991 (the Prof Zubov ship) and from Europe to south of the Equator (8° S to ~ 40° N) between January and February 1992 (the Prof Vizeship). Our philosophy with the data recovery is to follow the same algorithms and parameters appearing in the two peer-reviewed articles that presented these datasets in the same issue of GRL in 1993, and here we provide all 48 lidar soundings made from the Prof. Zubov, and 11 of the 20 conducted from the Prof. Vize, ensuring we have reproduced the aerosols backscatter and extinction values in the Figures of those two papers. These original approaches used thermodynamic properties from the CIRA-86 standard atmosphere to derive the molecular backscattering, vertically and temporally constant values applied for the aerosol backscatter to extinction ratio and the correction factor of the aerosols backscattering wavelength dependence. We demonstrate this initial validation of the recovered stratospheric aerosol extinction profiles, providing full details of each dataset in this paper's Supplement S1, the original text files of the backscatter ratio, the calculated aerosols backscatter and extinction profiles. We anticipate the data providing potential new observational case studies for modelling analyses, including a 1-week series of consecutive soundings (in September 1991) at the same location showing the progression of the entrainment of part of the Pinatubo plume into the upper troposphere and the formation of an associated cirrus cloud. The Zubov lidar dataset illustrates how the tropically confined Pinatubo aerosol cloud transformed from a highly heterogeneous vertical structure in August 1991, maximum aerosol extinction values around 19 km for the lower layer and 23-24 for the upper layer, to a more homogeneous and deeper reservoir of volcanic aerosol in September 1991. We encourage modelling groups to consider new analyses of the Pinatubo cloud, comparing to the recovered datasets, with the potential to increase our understanding of the evolution of the Pinatubo aerosol cloud and its effects. Data described in this work are available at https://doi.pangaea.de/10.1594/PANGAEA.912770 (Antuña-Marrero et al., 2020). [ABSTRACT FROM AUTHOR]