Pinatubo Volcanic Cloud Research Articles

Interactive Stratospheric Aerosol Microphysics‐Chemistry Simulations of the 1991 Pinatubo Volcanic Aerosols With Newly Coupled Sectional Aerosol and Stratosphere‐Troposphere Chemistry Modules in the NASA GEOS Chemistry‐Climate Model (CCM)

AbstractWe have coupled the GEOS‐Chem tropospheric‐stratospheric chemistry mechanism and the Community Aerosol and Radiation Model for Atmospheres (CARMA), a sectional aerosol microphysics module, within the NASA Goddard Earth Observing System Chemistry‐Climate Model (GEOS CCM) in order to simulate the interactions between stratospheric chemistry and aerosol microphysics. We use observations of the 1991 Mount Pinatubo volcanic cloud to evaluate this new version of the GEOS CCM. The GEOS‐Chem chemistry module is used to simulate the oxidation of sulfur dioxide (SO2) more realistically than assuming hydroxyl radical (OH) fields are constant, as OH concentrations in the plume decrease dramatically in the weeks following the eruption. CARMA simulates sulfate aerosols with dynamic microphysical and optical properties. The CARMA‐calculated aerosol surface area is coupled to the chemistry module from GEOS‐Chem for the calculation of heterogeneous chemistry. We use a set of observational and theoretical constraints for Pinatubo to evaluate the performance of this new version of the GEOS CCM. These simulations are specifically compared with satellite and in‐situ observations and provide insights into the connections between the gas‐phase chemistry and the aerosol microphysics of the early plume and how they impact the climatic and chemical changes following a large volcanic eruption. A second, smaller eruption is also included in these simulations, the 15 August 1991, eruption of Cerro Hudson in Chile, which we find essential in explaining the aerosol optical depth in the Southern Hemisphere in 1991.

Inverse Modeling of the Initial Stage of the 1991 Pinatubo Volcanic Cloud Accounting for Radiative Feedback of Volcanic Ash

AbstractThe way volcanic clouds evolve is very sensitive to the initial spatial 3D distributions of volcanic materials, which are often unknown. In this study, we conducted inverse modeling of the Mt. Pinatubo cloud using total ozone mapping spectrometer 2D mapping of Aerosol Index and SO2 loading during the first three post‐eruption days to estimate the time‐dependent emissions profiles and initial 3D spatial distributions of volcanic ash and SO2. We account for aerosol radiative feedback and dynamic lofting of volcanic ash in the inversion calculations for the first time. This resulted in a lower ash injection height (by 1.5 km for ash) than without ash radiative feedback. The Pinatubo eruption ejected ≈77% of fine ash at 12–23 km, ≈65% of SO2 at 18–25 km. In contrast with previous studies, which suggested that all volcanic materials were emitted above the tropopause, a significant fraction of SO2 (5.1 of 15.5 Mt) and fine ash (37.2 of 66.5 Mt) were ejected in the troposphere, where SO2 quickly oxidized into sulfate aerosol that is short‐lived in the troposphere. This explains the early presence of sulfate aerosols in the plume and why the models can reproduce the observed volcanic aerosols' optical depth (AOD), assuming lower‐than‐observed SO2 emission in the stratosphere. Despite the quicker than in observations build‐up of sulfate AOD, in a month after the eruption, the evolution of the Pinatubo AOD simulated using the obtained ash and SO2 initial distributions converges with the available stratospheric aerosol and gas experiment observations.

The effect of ash, water vapor, and heterogeneous chemistry on the evolution of a Pinatubo-size volcanic cloud

Abstract. We employ the ECHAM5/MESSy2 atmospheric chemistry general circulation model (EMAC) that incorporates calculations of gas-phase and heterogeneous chemistry coupled with the ozone cycle and aerosol formation, transport, and microphysics to calculate the 1991 Pinatubo volcanic cloud. We considered simultaneous injections of SO2, volcanic ash, and water vapor. We conducted multiple ensemble simulations with different injection configurations to test the evolution of SO2, SO42-, ash masses, stratospheric aerosol optical depth, surface area density (SAD), and the stratospheric temperature response against available observations. We found that the volcanic cloud evolution is sensitive to the altitude where volcanic debris is initially injected and the initial concentrations of the eruption products that affect radiative heating and lofting of the volcanic cloud. The numerical experiments with the injection of 12 Mt SO2, 75 Mt of volcanic ash, and 150 Mt of water vapor at 20 km show the best agreement with the observation aerosol optical depth and stratospheric temperature response. Volcanic water injected by eruptive jet and/or intruding through the tropopause accelerates SO2 oxidation. But the mass of volcanic water retained in the stratosphere is controlled by the stratospheric temperature at the injection level. For example, if volcanic materials are released in the cold point above the tropical tropopause, most of the injected water freezes and sediments as ice crystals. The water vapor directly injected into the volcanic cloud increases the SO42- mass and stratospheric aerosol optical depth by about 5 %. The coarse ash comprises 98 % of the ash injected mass. It sediments within a few days, but aged submicron ash could stay in the stratosphere for a few months providing SAD for heterogeneous chemistry. The presence of ash accelerates the SO2 oxidation by 10 %–20 % due to heterogeneous chemistry, radiative heating, lofting, and faster dispersion of volcanic debris. Ash aging affects its lifetime and optical properties, almost doubling the ash radiative heating. The 2.5-year simulations show that the stratospheric temperature anomalies forced by radiative heating of volcanic debris in our experiments with the 20 km injection height agree well with observations and reanalysis data. This indicates that the model captures the long-term evolution and climate effect of the Pinatubo volcanic cloud. The volcanic cloud's initial lofting, facilitated by ash particles' radiative heating, controls the oxidation rate of SO2. Ash accelerates the formation of the sulfate layer in the first 2 months after the eruption. We also found that the interactive calculations of OH and heterogeneous chemistry increase the volcanic cloud sensitivity to water vapor and ash injections. All those factors must be accounted for in modeling the impact of large-scale volcanic injections on climate and stratospheric chemistry.

Investigation of weather anomalies in the low-latitude islands of the Indian Ocean in 1991

Abstract. Temperature, precipitation and sunshine duration measurements at meteorological stations across the southern Indian Ocean have been analysed to try to differentiate the possible influence of the Mount Pinatubo volcanic eruption in the Philippines in June 1991 and the normal weather forcings. During December 1991, precipitation on the tropical islands Glorieuses (11.6° S) and Mayotte (12.8° S) was 4 and 3 times greater, respectively, than the climatological mean (precipitation is greater by more than than twice the standard deviation (SD)). Mean sunshine duration (expressed in sun hours per day) was only 6 h on Mayotte, although the sunshine duration is usually more than 7.5 ± 0.75 h, and on the Glorieuses it was only 5 h, although it is usually 8.5 ± 1 h. Mean and SD of sunshine duration are based on December (1964–2001 for Mayotte, 1966–1999 for the Glorieuses). The Madden–Julian Oscillation (MJO) is shown to correlate best with precipitation in this area. Variability controlling the warm zone on these two islands can be increased by the Indian Ocean Dipole (IOD), El Niño, the quasi-biennial oscillation (QBO) and/or solar activity (sunspot number, SSN). However, temperature records of these two islands show weak dependence on such forcings (temperatures are close to the climatological mean for December). This suggests that such weather forcings have an indirect effect on the precipitation. December 1991 was associated with unusually low values of the MJO index, which favours high rainfall, as well as with El Niño, eastern QBO and high SSN, which favour high variability. It is therefore not clear whether the Mount Pinatubo volcanic eruption had an effect. Since the precipitation anomalies at the Glorieuses and Mayotte are more or less local (Global Precipitation Climatology Project (GPCP) data) and the effect of the Pinatubo volcanic cloud should be more widespread, it seems unlikely that Pinatubo was the cause. Islands at higher southern latitudes (south of Tromelin at 15.5° S) were not affected by the Pinatubo eruption in terms of sunshine duration, precipitation or temperature.

Particles in the great Pinatubo volcanic cloud of June 1991: The role of ice

Pinatubo's 15 June 1991 eruption was Earth's largest of the last 25 years, and it formed a substantial volcanic cloud. We present results of analysis of satellite‐based infrared remote sensing using Advanced Very High Resolution Radiometer (AVHRR) and TIROS Operational Vertical Sounder/High Resolution Infrared Radiation Sounder/2 (TOVS/HIRS/2) sensors, during the first few days of atmospheric residence of the Pinatubo volcanic cloud, as it drifted from the Philippines toward Africa. An SO2‐rich upper (25 km) portion drifted westward slightly faster than an ash‐rich lower (22 km) part, though uncertainty exists due to difficulty in precisely locating the ash cloud. The Pinatubo clouds contained particles of ice, ash, and sulfate which could be sensed with infrared satellite data. Multispectral IR data from HIRS/2 were most useful for sensing the Pinatubo clouds because substantial amounts of both ice and ash were present. Ice and ash particles had peak masses of about 80 and 50 Mt, respectively, within the first day of atmospheric residence and declined very rapidly to values that were <10 Mt within 3 days. Ice and ash declined at a similar rate, and it seems likely that ice and ash formed mixed aggregates which enhanced fallout. Sulfate particles were detected in the volcanic cloud by IR satellites very soon after eruption, and their masses increased systematically at a rate consistent with their formation from SO2, which was slowly decreasing in mass during the same period. The initially detected sulfate mass was 4 Mt (equivalent to 3 Mt SO2) and after 5 days was 12–16 Mt (equivalent to 9–12 Mt SO2).

Simulation of Mt. Pinatubo Volcanic Aerosol with the Hamburg Climate Model ECHAM4

We study the three-dimensional transport of Mt. Pinatubo volcanic cloud with the climate model ECHAM4. In order to obtain model results comparable with observations a Newtonian relaxation technique was applied, which forces prognostic model variables towards the observations. A comparison of the simulated aerosol distribution with satellite data reveals good agreement for the first months after the eruption. The model, however, is unable to simulate the tropical aerosol maximum in 1992 and also overestimates the vertical downward and northward transport of aerosols. Substantial improvement was achieved with the introduction of reduced advective vertical transport through the 380 K isentropic layer. Heating rates and top of the atmosphere fluxes, which were calculated online for the first half year after the eruption, are in the observed range. A comparison of Pinatubo simulations between three different vertical ECHAM4 versions (ECHAM4 L19, ECHAM4 L39, MA/ECHAM4) indicates that a vertical resolution of ≈ 700 m in the tropopause region is sufficient to realistically reduce the vertical transport through the tropopause. Consideration of the upper branch of the Brewer Dobson circulation in the MA/ECHAM4 model improves the geographical distribution of the volcanic cloud. The application of a relaxation technique can further reduce major shortcomings of stratospheric simulations with the standard climate model. There remain, however some critical points in the global transport characteristics in all three models which are not fully understood.

An Overview of Lidar Study in China.

The progress of lidar studies made in China is reviewed in the paper. The El Chichon volcaniccloud was measured with the ruby lidar in 1983. The large amounts of profile data of Pinatubovolcanic cloud have been obtained at Hefei and Beijing. The first Chinese ozone-DIALsystem has been constructed by Hu's group at AIOFM in 1993. Another ozone-DIAL lidarsystem is being constructed by Qiu's group at IAP. Chinese scientists have done many researchworks in the lidar measurements of the troposphere, such as plume dispersion, aerosol extinctioncoefficient profile, cloud base height, horizontal and slant visibility. Two lidar systems arebeing constructed for the middle atmosphere in China. The lidar, applied in measurements ofsea water temperature, and oil slicks at sea surface, has been developing in China also. Inaddition, Chinese scientists also did many theoretical studies in the methodologies of lidarmeasurements, multiple scattering in lidar measurement.

Radiatively forced dispersion of the Mt. Pinatubo volcanic cloud and induced temperature perturbations in the stratosphere during the first few months following the eruption

A combined 3‐dimensional circulation model and aerosol microphysical/transport model is used to simulate the dispersion of the Mt. Pinatubo volcanic cloud in the stratosphere for the first few months following the eruption. Radiative heating of the cloud due to upwelling infrared radiation from the troposphere is shown to be an important factor affecting the transport. Without cloud heating, cloud material stays mostly north of the equator, whereas with cloud heating, the cloud is transported southward across the equator within the first two weeks following the eruption. Generally the simulations agree with TOMS, AVHRR, and SAGE satellite observations showing the latitude distribution of cloud material to be between about 20°S and 30°N within the first few months. Temperature perturbations in the stratosphere induced by the aerosol heating are generally 1–4 K, in the range of those observed.

Heterogeneous Reaction Probabilities, Solubilities, and the Physical State of Cold Volcanic Aerosols

On 19 January 1992, heterogeneous loss of HNO(3), ClNO(3), and HCl was observed in part of the Mount Pinatubo volcanic cloud that had cooled as a result of forced ascent. Portions of the volcanic cloud froze near 191 kelvin. The reaction probability of ClNO(3) and the solubility of HNO(3) were close to laboratory measurements on liquid sulfuric acid. The magnitude of the observed loss of HCl suggests that it underwent a heterogeneous reaction. Such reactions could lead to substantial loss of HCl on background sulfuric acid particles and so be important for polar ozone loss.

日本のライダーネットワークを用いたピナトゥボ火山雲の観測

日本のライダーネットワークを用いたピナトゥボ火山雲の観測

Latitudinal survey of spectral optical depths of the Pinatubo volcanic cloud‐derived particle sizes, columnar mass loadings, and effects on planetary albedo

We have made airborne measurements of spectral optical depths, radiative fluxes, and scattered radiation fields during the NASA Caribbean mission (July 7–14, 1991) to characterize the Pinatubo volcanic cloud. In this paper we report the latitudinal and spectral dependence of the volcanic cloud's optical depth. From these measurements we determine moments of the particle size distribution. The change in planetary albedo induced by the volcanic cloud is calculated for the range of measured optical depths with the objective of assessing the impact on the solar radiation budget. Mid‐visible optical depths higher than 0.4 were observed, placing the Pinatubo stratospheric cloud among the thickest ever measured. The latitudinal distribution of extinction shows that by July 7, 1991 the volcanic cloud had extended to 30°N. The effective particle radius was determined to be between 0.18 μm and 035 μm with a corresponding columnar mass loading between 35 and 80 mg.m−2.