Arlin J. Krueger

Global tracking of the SO2 clouds from the June, 1991 Mount Pinatubo eruptions

The explosive June 1991 eruptions of Mount Pinatubo produced the largest sulfur dioxide cloud detected by the Total Ozone Mapping Spectrometer (TOMS) during its 13 years of operation: approximately 20 million tons of SO2, predominantly from the cataclysmic June 15th eruption. The SO2 cloud observed by the TOMS encircled the Earth in about 22 days (∼21 m/s); however, during the first three days the leading edge of the SO2 cloud moved with a speed that averaged ∼35 m/s. Compared to the 1982 El Chichon eruptions, Pinatubo outgassed nearly three times the amount of SO2 during its explosive phases. The main cloud straddled the equator within the first two weeks of eruption, whereas the El Chichon cloud remained primarily in the northern hemisphere. Our measurements indicate that Mount Pinatubo has produced a much larger and perhaps longer-lasting SO2 cloud; thus, climatic responses to the Pinatubo eruption may exceed those of El Chichon.

Sighting of El Chichon sulfur dioxide clouds with the Nimbus 7 total ozone mapping spectrometer

The eruptions of El Chich�n volcano on 28 March and 3 and 4 April 1982 were observed by the Nimbus 7 total ozone mapping spectrometer due to strong absorption by volcanic gases at the shortest wavelengths of the spectrometer (312.5 and 317.5 nanometers). These ultraviolet pictures permit a measurement of the volume, dispersion, and drift of volcanic gas clouds. The tropospheric clouds were rapidly dispersed in westerly winds while persistent stratospheric clouds drifted in easterly winds at speeds up to 13 meters per second. The spectral reflectance is consistent with sulfur dioxide absorption and rules out carbon disulfide as a major constituent. A preliminary estimate of the mass of sulfur dioxide deposited in the stratosphere by the large eruptions on 3 and 4 April is 3.3 x 106 tons. Prior estimates of volcanic cloud volume were based on extrapolation of locally measured sulfur dioxide concentrations.

Band residual difference algorithm for retrieval of SO/sub 2/ from the aura ozone monitoring instrument (OMI)

The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resolution, coupled with global coverage, for space-based UV measurements of sulfur dioxide (SO/sub 2/). This paper describes an OMI SO/sub 2/ algorithm (the band residual difference) that uses calibrated residuals at SO/sub 2/ absorption band centers produced by the NASA operational ozone algorithm (OMTO3). By using optimum wavelengths for retrieval of SO/sub 2/, the retrieval sensitivity is improved over NASA predecessor Total Ozone Mapping Spectrometer (TOMS) by factors of 10 to 20, depending on location. The ground footprint of OMI is eight times smaller than TOMS. These factors produce two orders of magnitude improvement in the minimum detectable mass of SO/sub 2/. Thus, the diffuse boundaries of volcanic clouds can be imaged better and the clouds can be tracked longer. More significantly, the improved sensitivity now permits daily global measurement of passive volcanic degassing of SO/sub 2/ and of heavy anthropogenic SO/sub 2/ pollution to provide new information on the relative importance of these sources for climate studies.

Volcanic sulfur dioxide measurements from the total ozone mapping spectrometer instruments

The total ozone mapping spectrometer (TOMS), first flown on the Nimbus 7 satellite, has delivered an unanticipated set of unique information about volcanic plumes because of its contiguous spatial mapping and use of UV wavelengths. The accuracies of TOMS sulfur dioxide retrievals, volcanic plume masses, and eruption totals under low-latitude conditions are evaluated using radiative transfer simulations and error analysis. The retrieval algorithm is a simultaneous solution of the absorption optical depth equations including ozone and sulfur dioxide at the four shortest TOMS wavelengths and an empirical correction based on background condition residuals. The retrieval algorithm reproduces model stratospheric sulfur dioxide plume amounts within ±10% over most central scan angles and moderate solar zenith angles if no aerosols or ash are present. The errors grow to 30% under large solar zenith angle conditions. Volcanic ash and sulfate aerosols in the plume in moderate optical depths (0.3) produce an overestimation of the sulfur dioxide by 15–25% depending on particle size and composition. Retrievals of tropospheric volcanic plumes are affected by the reflectivity of the underlying surface or clouds. The precision of individual TOMS SO2 soundings is limited by data quantization to ±6 Dobson units. The accuracy is independent of most instrument calibration errors but depends linearly on relative SO2 absorption cross-section errors at the TOMS wavelengths. Volcanic plume mass estimates are dependent on correction of background offsets integrated over the plume area. The errors vary with plume mass and area, thus are highly individual. In general, they are least for moderate size, compact plumes. Estimates of the total mass of explosively erupted sulfur dioxide depend on extrapolation of a series of daily plume masses backward to the time of the eruption. Errors of 15–30% are not unusual. Effusive eruption total mass estimates are more uncertain due to difficulties in separating new from old sulfur dioxide in daily observations.

Solar Proton Event: Influence on Stratospheric Ozone

Large-scale reductions in the ozone content of the middle and upper stratosphere over the polar cap regions were associated with the major solar proton event of 4 August 1972. This reduction, which was determined from measurements with the backscattered ultraviolet experiment on the Nimbus 4 satellite, is interpreted as being due to the catalytic destruction of ozone by odd-nitrogen compounds (NOx) produced by the event.

The Nimbus-4 Backscatter Ultraviolet (BUV) atmospheric ozone experiment — tow years' operation

SummaryIn April 1970 the Backscatter Ultraviolet (BUV) experiment was placed into orbit aboard the Nimbus-4 satellite. This double monochromator experiment measures ultraviolet terrestrial radiance at twelve discrete wavelengths between 2550 Å and 3400 Å. Approximately 100 scans covering a 230 km square are made between terminator crossings on the daylight side of the earth. A colinear photometer channel with the same field of view is used to derive the Lambert reflectivity of the lower boundary of the scattering atmosphere. The extraterrestrial solar irradiance is measured at the northern terminator. The instrument has currently produced almost three years of nearly continuous data which are being used to infer the high-level ozone distribution and total ozone on a global basis. The high-level ozone data have been verified by independent coincident rocket ozone soundings, and the total ozone values show good agreement with Dobson spectrophotometer determinations as well as those made with the Infrared Interferometer Spectrometer also on Nimbus-4. An increase has been observed in equatorial radiance at 2550 Å relative to 2900 Å, which seems to indicate that the amount of ozone in the upper stratosphere is related to the eleven-year solar cycle.

Stratospheric loading of sulfur from explosive volcanic eruptions

This paper is an attempt to measure our understanding of volcano/atmosphere interactions by comparing a box model of potential volcanogenic aerosol production and removal in the stratosphere with the stratospheric aerosol optical depth over the period of 1979 to 1994. Model results and observed data are in good agreement both in magnitude and removal rates for the two largest eruptions, El Chichón and Pinatubo. However, the peak of stratospheric optical depth occurs about nine months after the eruptions, four times longer than the model prediction, which is driven by actual SO2 measurements. For smaller eruptions, the observed stratospheric perturbation is typically much less pronounced than modeled, and the observed aerosol removal rates much slower than expected. These results indicate several limitations in our knowledge of the volcano‐atmosphere reactions in the months following an eruption. Further, it is evident that much of the emitted sulfur from smaller eruptions fails to produce any stratospheric impact. This suggests a threshold whereby eruption columns that do not rise much higher than the tropopause (which decreases in height from equatorial to polar latitudes) are subject to highly efficient self‐removal processes. For low latitude volcanoes during our period of study, eruption rates on the order of 50,000 m3/s (dense rock equivalent) were needed to produce a significant global perturbation in stratospheric optical depth, i.e., greater than 0.001. However, at high (>40°) latitudes, this level of stratospheric impact was produced by eruption rates an order of magnitude smaller.

Volcanic eruption detection by the Total Ozone Mapping Spectrometer (TOMS) instruments: a 22-year record of sulphur dioxide and ash emissions

Abstract Since their first depolyment in November 1978, the Total Ozone Mapping Spectrometer (TOMS) instruments have provided a robust and near-continuous record of sulphur dioxide (SO2) and ash emissions from active volcanoes worldwide. Data from the four TOMS satellites that have flown to date have been analysed with the latest SO2/ash algorithms and incorporated into a TOMS volcanic emissions database that presently covers 22 years of SO2 and ash emissions. The 1978–2001 record comprises 102 eruptions from 61 volcanoes, resulting in 784 days of volcanic cloud observations. Regular eruptions of Nyamuragira (DR Congo) since 1978, accompanied by copious SO2 production, have contributed material on approximately 30% of the days on which clouds were observed. The latest SO2 retrieval results from Earth Probe (EP) TOMS document a period (1996–2001) lacking large explosive eruptions, and also dominated by SO2 emission from four eruptions of Nyamuragira. EP TOMS has detected the SO2 and ash produced during 23 eruptions from 15 volcanoes to date, with volcanic clouds observed on 158 days. The EP TOMS instrument began to degrade in 2001, but has now stabilized, although its planned successor (QuikTOMS) recently failed to achieve orbit. New SO2 algorithms are currently being developed for the Ozone Monitoring Instrument, which will continue the TOMS record of UV remote sensing of volcanic emissions from 2004 onwards.

Early evolution of a stratospheric volcanic eruption cloud as observed with TOMS and AVHRR

This paper is a detailed study of remote sensing data from the total ozone mapping spectrometer (TOMS) and the advanced very high resolution radiometer (AVHRR) satellite detectors, of the 1982 eruption of El Chichon, Mexico. The volcanic cloud/atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud [Krueger et al., 1995] with thermal infrared retrievals of the size, optical depth, and mass of fine-grained (1–10 μm radius) volcanic ash [Wen and Rose, 1994]. Our study provides the first direct evidence of gravitational separation of ash from a stratospheric, gas-rich, plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds. The eruption column reached as high as 32 km [Carey and Sigurdsson, 1986] and was injected into an atmosphere with a strong wind shear, which allowed for an observation of the separation of sulfur dioxide and volcanic ash. The upper, more sulfur dioxide-rich part of the cloud was transported to the west in the stratosphere, while the fine-grained ash traveled to the south in the troposphere. The mass of sulfur dioxide released was estimated at 7.1 × 109 kg with the mass decreasing by approximately 4% 1 day after the peak. The mass of fine-grained volcanic ash detected was estimated at 6.5 × 109 kg, amounting to about 0.7% of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano. Over the following days, 98% of this remaining fine ash was removed from the volcanic cloud, and the effective radius of ash in the volcanic cloud decreased from about 8 μm to about 4 μm.

A simulation of the Cerro Hudson SO2 cloud

An isentropic trajectory model is used to simulate the evolution of the southern hemisphere SO2 cloud associated with the eruption of Cerro Hudson. By matching the parcel trajectories with total ozone mapping spectrometer SO2 retrievals, the principal stratospheric injection region is determined to be between 11 and 16 km in altitude. This region is characterized by weak wind shears and is located just poleward of the subtropical jet in the outer fringe of the stratospheric polar vortex. The lack of wind shear in the injection region explains the slow zonal dispersal of the SO2 cloud which was still clearly observed 19 days after the eruption. The trajectory model simulation of the SO2 cloud shows good agreement with observations for 7 days after the eruption. Using the potential vorticity and potential temperature estimates of the initial eruption cloud, the cloud position relative to the polar night jet is shown to be nearly fixed up to September 2, 1991, which was as long as the cloud was observed. This result suggests that the lower stratospheric polar and mid-latitude regions are nearly isolated from each other during the late August period.