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The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument operated from 25 October 1978 through 28 May 1979. Its version 6 (V6) profiles were processed and archived in 2002. We present several diagnostic examples of the quality of the V6 stratospheric species distributions based on their level 3 zonal Fourier coefficient products. In particular, we show that there are small differences in the ascending (A) minus descending (D) orbital temperature–pressure or T(p) profiles (their A−D values) that affect (A−D) species values. Systematic A−D biases in T(p) can arise from small radiance biases and/or from viewing anomalies along orbits. There can also be (A−D) differences in T(p) due to not resolving and correcting for all of the atmospheric temperature gradient along LIMS tangent view-paths. An error in T(p) affects species retrievals through (1) the Planck blackbody function in forward calculations of limb radiance that are part of the iterative retrieval algorithm of LIMS, and (2) the registration of the measured LIMS species radiance profiles in pressure altitude, mainly for the lower stratosphere. There are clear A−D differences for ozone, H2O, and HNO3 but not for NO2. Percentage differences are larger in the lower stratosphere for ozone and H2O because those species are optically thick. We evaluate V6 ozone profile biases in the upper stratosphere with the aid of comparisons against a monthly climatology of UV–ozone soundings from rocketsondes. We also provide results of time series analyses of V6 ozone, H2O, and potential vorticity for the middle stratosphere to show that their average (A+D) V6 level 3 products provide a clear picture of the evolution of those tracers during Northern Hemisphere winter. We recommend that researchers use the average V6 level 3 product for their science studies of stratospheric ozone and H2O, while keeping in mind that there are uncorrected nonlocal thermodynamic equilibrium effects in daytime ozone in the lower mesosphere and in daytime H2O in the uppermost stratosphere. We also point out that the present-day Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment provides measurements and retrievals of temperature and ozone that are nearly free of anomalous diurnal variations and of effects from gradients at low and middle latitudes.

The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument operated from 25 October 1978 through 28 May 1979. This note focuses on its Version 6 (V6) data and indications of ozone loss in the lower stratosphere of the Southern Hemisphere subpolar region during the last week of October 1978. We provide profiles and maps that show V6 ozone values of only 2 to 3 ppmv at 46 hPa within the edge of the polar vortex near 60∘ S from late October through mid-November 1978. There are also low values of V6 nitric acid (∼3 to 6 ppbv) and nitrogen dioxide (

The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument operated from October 25, 1978, through May 28, 1979. Its Version (V6) profiles were processed and archived in 2002. We present several diagnostic examples of the quality of the V6 stratospheric ozone and water vapor data based on their Level 3 zonal Fourier coefficient products. In particular, we show that there are small differences in the ascending (A) minus descending (D) orbital temperature-pressure or T(p) profiles (their A-D values) that affect (A-D) ozone and water vapor. Systematic A-D biases in T(p) can arise from small radiance biases and/or from viewing anomalies along orbits. There can also be (A-D) differences in T(p) due to not resolving and correcting for all of the atmospheric temperature gradient along LIMS tangent view-paths. An error in T(p) affects the retrievals of ozone and water vapor through: (1) the Planck blackbody function in forward calculations of limb radiance that are part of the iterative retrieval algorithm of LIMS, and (2) the registration of the measured LIMS species radiance profiles in pressure-altitude, particularly for the lower stratosphere. We evaluate V6 ozone profile biases in the upper stratosphere with the aid of comparisons against a monthly climatology of UV-ozone soundings from rocketsondes. We also provide results of time series analyses of V6 ozone, water vapor, and potential vorticity for the middle stratosphere to show that their average (A+D) V6 Level 3 products provide a clear picture of the evolution of those tracers during northern hemisphere winter. We recommend that researchers use the average V6 Level 3 data for their science studies of stratospheric ozone and water vapor wherever diurnal variations of them are unexpected. We also point out that the present-day Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment is providing measurements and retrievals of temperature and ozone, which are essentially free of any anomalous diurnal variations.

The Nimbus 7 limb infrared monitor of the stratosphere (LIMS) instrument operated from October 25, 1978, through May 28, 1979. This paper focuses on its Version (V6) data for the lower stratosphere of the southern hemisphere, subpolar region during the last week of October 1978. We provide profiles and maps that show V6 ozone values of only 2 to 3 ppmv within the edge of the polar vortex at 46 hPa near 60° S from late October through mid-November 1978. There are also low values of V6 nitric acid (∼ 3 to 6 ppbv) and nitrogen dioxide (first light LIMS observations provide the earliest, space-based view of conditions within the lower stratospheric ozone layer of the southern polar region in springtime.

A series of young adult patients developed solar retinopathy during sun exposure over a two-day period in a particular region of the United States during March of 1986. Evaluation of the photobiological and geophysical parameters involved in solar retinitis are presented. A multifactorial pathogenesis is proposed. Of interest, a possible increase in terrestrial ultra-violet B radiation secondary to a localized relatively low ozone column during the days involved may have contributed to the retinal damage. Recommendations for protection from solar retinitis are noted.

We present daily measurements of sulfur dioxide (SO2) emissions from active volcanoes in Ecuador and southern Colombia between September 2004 and September 2006, derived from the Ozone Monitoring Instrument (OMI) on NASA's EOS/Aura satellite. OMI is an ultraviolet/visible spectrometer with an unprecedented combination of spatial and spectral resolution, and global coverage, that permits daily measurements of passive volcanic degassing from space. We use non-interactive processing methods to automatically extract daily SO2 burdens and information on SO2 sources from the OMI datastream. Maps of monthly average SO2 vertical columns retrieved by OMI over Ecuador and S. Colombia are also used to illustrate variations in regional SO2 loading and to pinpoint sources. The dense concentration of active volcanoes in Ecuador provides a stringent test of OMI's ability to distinguish SO2 from multiple emitting sources. Our analysis reveals that Tungurahua, Reventador and Galeras were responsible for the bulk of the SO2 emissions in the region in the timeframe of our study, with no significant SO2 discharge detected from Sangay. At Galeras and Reventador, we conclude that OMI can detect variations in SO2 release related to cycles of conduit sealing and degassing, which are a critical factor in hazard assessment. The OMI SO2 data for Reventador are the most extensive sequence of degassing measurements available for this remote volcano, which dominated regional SO2 production in June–August 2005. At Tungurahua, the OMI measurements span the waning stage of one eruptive cycle and the beginning of another, and we observe increasing SO2 burdens in the months prior to explosive eruptions of the volcano in July and August 2006. Cumulative SO2 loadings measured by OMI yield a total of ~ 1.16 Tg SO2 emitted by volcanoes on mainland Ecuador/S. Colombia between September 2004 and September 2006; as much as 95% of this SO2 may originate from non-eruptive degassing. Approximate apportionment of the total SO2 loading indicates that ~ 40% originated from Tungurahua, with ~ 30% supplied by both Reventador and Galeras. These measurements of volcanic SO2 degassing in Ecuador confirm OMI's potential as an effective, economical and risk-free tool for daily monitoring of SO2 emissions from hazardous volcanoes.

The 1982 eruption of El Chichon inspired a new technique for monitoring volcanic clouds. Data from the Total Ozone Mapping Spectrometer (TOMS) instrument on the Nimbus-7 satellite were used to measure sulfur dioxide in addition to ozone. For the first time precise data on the sulfur dioxide mass in even the largest explosive eruption plumes could be determined. The plumes could be tracked globally as they are carried by winds. Magmatic eruptions could be discriminated from phreatic eruptions. The data from El Chichon are reanalyzed in this paper using the latest version of the TOMS instrument calibration (V8). They show the shearing of the eruption cloud into a globe-circling band while still anchored over Mexico in three weeks. The measured sulfur dioxide mass in the initial March 28 eruption was 1.6 Tg; the April 3 eruption produced 0.3 Tg more, and the April 4 eruptions added 5.6 Tg, for a cumulative total of 7.5 Tg, in substantial agreement with estimates from prior data versions. TOMS Aerosol Index (absorbing aerosol) data show rapid fallout of dense ash east and south of the volcano in agreement with Advanced Very High Resolution Radiometer (AVHRR) ash cloud positions.

The Dutch-Finnish Ozone Monitoring Instrument (OMI) launched on the NASA Aura satellite in July 2004 offers unprecedented spatial resolution, coupled with contiguous daily global coverage, for space-based UV measurements of sulfur dioxide (SO2). We present a first validation of the OMI SO2 data with in situ aircraft measurements in NE China in April 2005. The study demonstrates that OMI can distinguish between background SO2 conditions and heavy pollution on a daily basis. The noise (expressed as the standard deviation,sigma) is approximately 1.5 DU (Dobson units; 1 DU = 2.69 10 (exp 16) molecules/cm (exp 2)) for instantaneous field of view boundary layer (PBL) SO2 data. Temporal and spatial averaging can reduce the noise to sigma approximetly 0.3 DU over a remote region of the South Pacific; the long-term average over this remote location was within 0.1 DU of zero. Under polluted conditions collection 2 OMI data are higher than aircraft measurements by a factor of two. Improved calibrations of the radiance and irradiance data (collection 3) result in better agreement with aircraft measurements on polluted days. The air mass corrected collection 3 data still show positive bias and sensitivity to UV absorbing aerosols. The difference between the in situ data and the OMI SO2 measurements within 30 km of the aircraft profiles was about 1 DU, equivalent to approximately 5 ppb from 0 to 3000 m altitude. Quantifying the SO2 and aerosol profiles and spectral dependence of aerosol absorption between 310 and 330 nm are critical for an accurate estimate of SO2 from satellite UV measurements.

To improve global measurements of atmospheric sulfur dioxide (SO2), we have developed a new technique, called the linear fit (LF) algorithm, which uses the radiance measurements from the Ozone Monitoring Instrument (OMI) at a few discrete ultraviolet wavelengths to derive SO2, ozone, and effective reflectivity simultaneously. We have also developed a sliding median residual correction method for removing both the along- and cross-track biases from the retrieval results. The achieved internal consistencies among the LF-retrieved geophysical parameters clearly demonstrate the success of this technique. Comparison with the results from the Band Residual Difference technique has also illustrated the drastic improvements of this new technique at high SO2 loading conditions. We have constructed an error equation and derived the averaging kernel to characterize the LF retrieval and understand its limitations. Detailed error analysis has focused on the impacts of the SO2 column amounts and their vertical distributions on the retrieval results. The LF algorithm is robust and fast; therefore it is suitable for near real-time application in aviation hazards and volcanic eruption warnings. Very large SO2 loadings (>100 DU) require an off-line iterative solution of the LF equations to reduce the retrieval errors. Both the LF and sliding median techniques are very general so that they can be applied to measurements from other backscattered ultraviolet instruments, including the series of Total Ozone Mapping Spectrometer (TOMS) missions, thereby offering the capability to update the TOMS long-term record to maintain consistency with its OMI extension. Copyright 2007 by the American Geophysical Union. U7 - Export Date: 2 August 2010 U7 - Source: Scopus U7 - Art. No.: D24S43

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.

In this study, a methodology is proposed for incorporating total column ozone data from the Total Ozone Mapping Spectrometer (TOMS) into the initial conditions of a mesoscale prediction model. Based on the strong correlation between vertical mean potential vorticity (MPV) and TOMS ozone (O3) that was found in middle latitudes at both 30- and 90-km resolutions, using either analyses or 24-h model forecasts, a statistical correlation model between O3 and MPV is employed for assimilating TOMS ozone in a four-dimensional variational data assimilation (4DVAR) procedure. A linear relationship between O3 and MPV is first assumed: O3 = α(MPV) + β. The constants α and β are then found by a regression method. The proposed approach of using this simple linear regression model for ozone assimilation is applied to the prediction of the 24–25 January 2000 East Coast winter storm. Three 4DVAR experiments are carried out assimilating TOMS ozone, radiosonde, or both types of observations. It is found that adjustm...

* Joint Center for Earth Systems Technology (NASA/UMBC), University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21231, USA. Email: scarn@umbc.edu † Department of Geological Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA. ‡ Goddard Earth Sciences and Technology (GEST) Center, Code 916, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.

The quantitative relationship between ozone and potential vorticity, and hence balanced wind and temperature, is examined using observations collected for a one-month period by the total ozone mapping spectrometer (TOMS). Ozone data are compared with Ertel potential vorticity (PV) integrated vertically from 500 to 50 mb, obtained from the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis archive. By performing a simple time filtering we isolate synoptic-scale transients in the ozone and PV. We show that the previously reported high correlation between PV and ozone is actually variable from day to day. the correlation also shows strong latitudinal dependence, with essentially no correlation in the tropics and high correlation in middle latitudes. A method is introduced to derive a three-dimensional PV representation from ozone data and a background field taken from the reanalysis data. PV-inversion methods are then used to recover balanced winds and temperatures and geopotential heights which may be compared to the analysed fields. Results suggest that many of the upper-tropospheric synoptic-scale wind perturbations may be recovered from the ozone data. A systematic error in the retrieval method used here is the understimation of the strength of upper-level ridges, corresponding to an excess of vertically integrated ozone compared with integrated PV. We discuss reasons for this difference.

Volcanic eruptions loft gases and ash particles into the atmosphere and produce effects that are both short term (aircraft hazards, interference with satellite measurements) and long term (atmospheric chemistry, climate). Large (greater than 0.5mm) ash particles fall out in minutes [Rose et al, 1995], but fine ash particles can remain in the atmosphere for many days. This fine volcanic ash is a hazard to modem jet aircraft because the operating temperatures of jet engines are above the solidus temperature of volcanic ash, and because ash causes abrasion of windows and airframe, and disruption of avionics. At large distances(10(exp 2)-10(exp 4) km or more) from their source, drifting ash clouds are increasingly difficult to distinguish from meteorological clouds, both visually and on radar [Rose et al., 1995]. Satellites above the atmosphere are unique platforms for viewing volcanic clouds on a global basis and measuring their constituents and total mass. Until recently, only polar AVHRR and geostationary GOES instruments could be used to determine characteristics of drifting volcanic ash clouds using the 10-12 micron window [Prata 1989; Wen and Rose 1994; Rose and Schneider 1996]. The NASA Total Ozone Mapping Spectrometer (TOMS) instruments aboard the Nimbus-7, Meteor3, ADEOS, and Earth Probe satellites have produced a unique data set of global SO2 volcanic emissions since 1978 (Krueger et al., 1995). Besides SO2, a new technique has been developed which uses the measured spectral contrast of the backscattered radiances in the 330-380nm spectral region (where gaseous absorption is negligible) in conjunction with radiative transfer models to retrieve properties of volcanic ash (Krotkov et al., 1997) and other types of absorbing aerosols (Torres et al., 1998).

On August 19, 1992, the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA-12 and NASA's Total Ozone Mapping Spectrometer (TOMS) onboard the Nimbus-7 satellite simultaneously detected and mapped the ash cloud from the eruption of Mt. Spurr, Alaska. The spatial extent and geometry of the cloud derived from the two datasets are in good agreement and both AVHRR split window IR (11–12µm brightness temperature difference) and the TOMS UV Aerosol Index (0.34–0.38µm ultraviolet backscattering and absorption) methods give the same range of total cloud ash mass. Redundant methods for determination of ash masses in drifting volcanic clouds offer many advantages for potential application to the mitigation of aircraft hazards.

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 B STRA C T 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 Chichon 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 m 3 /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.

This paper proposes a volcanic SO2 index (VSI), on the basis of a 15-year satellite sampling of volcanic eruptions. This index is scaled to be compatible with the commonly cited volcanic explosivity index (VEI) used to compare explosive volcanic eruptions. A range of SO2 for each VEI level is proposed so that estimates of SO2 emission can be made from the historic VEI database. Volcanic SO2 from large eruptions can be routinely measured by satellite instruments, and for the smaller eruptions, where the sensitivity of satellite remote sensing is not sufficient, ground-based measurements are becoming more available. At the present time we do not think SO2 can be used to define an accurate climate-perturbation index, as we have both insufficient data on volcanic SO2 and understanding of the volcano-climate relationship.

The total ozone mapping spectrometer (TOMS) instruments have detected every significant volcanic eruption from November 1978 to December 1994 on the Nimbus 7 and Meteor 3 satellites and since July 1996 on the new satellites, TOMS-Earth Probe and ADEOS. We apply a radiative transfer model to simulate the albedos of these fresh eruption clouds to study the limitations of the present algorithm which assumes an absorbing cloud above a scattering atmosphere. The conditions are found to be approximated when the total absorption optical depth is less than 2 (i.e., 100 Dobson units (DU) SO 2 at 312 nm or 300 DU SO 2 at 317 nm). The spectral dependence of the albedo of a nonabsorbing Rayleigh atmosphere can be specified by only two parameters which are uniquely different when ash or sulfate aerosols are present in the stratosphere. However, the interaction between ash scattering and SO 2 absorption within a volcanic cloud produces a nonlinear effect at strongly absorbing wavelengths that accounts for overestimation of sulfur dioxide in ash-laden volcanic clouds by the Krueger et al. [1995] algorithm. Correction of this error requires knowledge of the ash properties. A method for determining two of the ash parameters from the longer TOMS wavelengths is described. Given the altitude of the cloud, surface reflectivity, and an estimate of effective variance of the ash size distribution, the optical thickness and either the effective radius or the index of refraction can be deduced. The ash retrievals are also needed to evaluate the tephra/gas ratio of eruptions and to compare the ash properties of different volcanoes.

Since sulfur dioxide in volcanic eruption clouds was first measured by the total ozone mapping spectrometer (TOMS) in 1983 [Krueger, 1983], SO2 released from dozens of eruptions has been quantified. Such measurements are invaluable for addressing such problems as global climate change and dynamics, understanding the physical and chemical processes of magma chambers and volcanic eruptions, and volcanic hazards. However, validating the TOMS SO2 retrievals has been difficult due to the fleeting nature of volcanic clouds. An important goal of this validation program is to extend the range of eruptions that can be accurately measured by both ground and satellite instruments.

The "mystery" volcanic aerosols observed in early 1982 were produced by the eruption of Nyamuragira in eastern Zaire. Large sulfur dioxide clouds associated with this volcano were found in the total ozone mapping spectrometer data beginning on December 26, 1981, continuing into early January 1982. This fissure eruption produced 3 million tons of sulfur dioxide in clouds that rose only to the tropopause level on the basis of winds and inferred chemical loss rates (about 20%/day), which are faster than stratospheric loss rates. Two thirds of the SO 2 was produced in the first 3 days of the eruption. In the 1980s this eruption was exceeded in sulfur dioxide output only by the April 1982 eruption of E1 Chichon.

from OMI column measurements observed far from the volcano. Using observations fromthe November 2006 eruption of Nyamuragira, back trajectories are run and statisticalanalyses are computed based on the distance of closest approach to the volcano. Thesestatistical analyses provide information about the emission height time series of SO

Galunggung volcano, Java, awoke from a 63-year quiescence in April 1982, and erupted sporadically through January 1983. During its most violent period from April to October, the Cikasasah Volcano Observatory reported 32 large and 56 moderate to small eruptions. From April 5 through September 19 the Total Ozone Mapping Spectrometer (TOMS), carried on NASA's Nimbus-7 satellite, detected and measured 24 different sulfur dioxide clouds; an estimated 1730 kilotons (kt) of SO2 were outgassed by these explosive eruptions. The trajectories, and rapid dispersion rates, of the SO2 clouds were consistent with injection altitudes below the tropopause. An additional 300 kt of SO2 were estimated to have come from 64 smaller explosive eruptions, based on the detection limit of the TOMS instrument. For the first time, an extended period of volcanic activity was monitored by remote sensing techniques which enabled observations of both the entire SO2 clouds produced by large explosive eruptions (using TOMS), and the relatively lower levels of SO2 emissions during non-explosive outgassing (using the Correlation Spectrometer, or COSPEC). Based on COSPEC measurements from August 1982 to January 1983, and on the relationship between explosive and non-explosive degassing, approximately 400 kt of SO2 were emitted during non-explosive activity. The total sulfur dioxide outgassed from Galunggung volcano from April 1982 to January 1983 is calculated to be 2500 kt (± 30%) from both explosive and non-explosive activity. While Galunggung added large quantities of sulfur dioxide to the atmosphere, its sporadic emissions occurred in relatively small events distributed over several months, and reached relatively low altitudes, and are unlikely to have significantly affected aerosol loading of the stratosphere in 1982 by volcanic activity.

The mass of SO 2 emitted by the 16 major explosive eruptions of Redoubt Volcano between December 1989 and April 1990 have been examined by the Total Ozone Mapping Spectrometer (TOMS) carried on the Nimbus 7 satellite. Because of low light levels during the winter months, TOMS could not detect SO 2 at high northern latitudes. Thus, the major eruptions from December through February could not be monitored unless winds brought the clouds to latitudes lower than about 58°N. Only two SO 2 clouds were observed in the satellite data — an approximately 100-kiloton (kt) cloud on December 16 over Nevada and eastern California, and a 10-kt cloud on March 9 directly over the volcano. We speculate that the major eruption on December 15 at 1015 hour produced the 100-kt cloud seen on December 16, and the mass of SO 2 injected into the atmosphere at that time was 175 ± 50 kt.

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 midlatitude regions are nearly isolated from each other during the late August period.

We describe the physical processes by which a vertically localized absorber perturbs the top-of-atmosphere solar backscattered ultraviolet (UV) radiance. The distinct spectral responses to perturbations of an absorber in its column amount and layer altitude provide the basis for a practical satellite retrieval technique, the Extended Iterative Spectral Fitting (EISF) algorithm, for the simultaneous retrieval of these quantities of a SO2 plume. In addition, the EISF retrieval provides an improved UV aerosol index for quantifying the spectral contrast of apparent scene reflectance at the bottom of atmosphere bounded by the surface and/or cloud; hence it can be used for detection of the presence or absence of UV absorbing aerosols. We study the performance and characterize the uncertainties of the EISF algorithm using synthetic backscattered UV radiances, retrievals from which can be compared with those used in the simulation. Our findings indicate that the presence of aerosols (both absorbing and nonabsorbing) does not cause large errors in EISF retrievals under most observing conditions when they are located below the SO2 plume. The EISF retrievals assuming a homogeneous field of view can provide accurate column amounts for inhomogeneous scenes, but they always underestimate the plume altitudes. The EISF algorithm reduces systematic errors present in existing linear retrieval algorithms that use prescribed SO2 plume heights. Applying the EISF algorithm to Ozone Monitoring Instrument satellite observations of the recent Kasatochi volcanic eruption, we demonstrate the successful retrieval of effective plume altitude of volcanic SO2, and we also show the improvement in accuracy in the corresponding SO2 columns.

[1] The ozone monitoring instrument (OMI), launched on the EOS/Aura satellite in July 2004, makes daily global observations of natural and anthropogenic SO2 emissions with unprecedented spatial resolution. Here we present the first robust comparison of OMI volcanic SO2 retrievals with ground−based instrumentation, using direct Sun observations of the Okmok volcanic cloud from Washington State University (WSU) in Pullman, WA on 18–20 July 2008. These measurements were made by the multifunction differential optical absorption spectroscopy (MFDOAS) instrument developed at WSU, as the Okmok cloud drifted over Pullman in the upper troposphere and lower stratosphere (UTLS). Observation conditions were favorable with cloud-free skies and a relatively homogeneous volcanic cloud distribution on OMI ground pixel scales (∼20–50 km). Movement of the Okmok cloud north and south of Pullman over a period of several days permitted comparison with three OMI overpasses with SO2 column amounts above the SO2 background level. The total SO2 columns measured by MFDOAS during OMI overpasses were 3.11 ± 0.23 Dobson units (DU), 1.75 ± 0.16 DU and 1.22 ± 0.18 DU (1 DU = 2.69 × 1016 molecules/cm2 = 0.029 g/m2). Comparison of ground-based direct Sun and operational and off-line OMI retrievals show an excellent agreement, providing the first validation of OMI measurements of volcanic SO2 in the UTLS.

The 1991 Antarctic springtime ozone decline, as measured by the Total Ozone Mapping Spectrometer (TOMS), was similar to those of earlier deep ozone hole years, 1987, 1989, and 1990. The minimum total ozone value was recorded on October 5, 1991 at 108 Dobson units near the South Pole. This was 8 DU lower than in any of the earlier years. Four of the last five years have exhibited an extensive, deep ozone hole. The area of the hole was about the same as in 1987, 1989, and 1990. The recovery of the low total ozone values occurred in mid-November as the polar vortex broke up.

Sulfur dioxide, a short-lived atmospheric constituent, is oxidized to sulfate aerosols, a climate agent. Main sources are volcanoes, smelters, and fossil fuel combustion. Satellite monitoring of SO2 began with TOMS data in 1978 that detected volcanic eruption clouds. Hyperspectral instruments, like OMI and GOME, have a twenty-fold improvement in sensitivity. Degassing volcanoes, smelters, and large power plants are now monitored for a database of SO2 emission to the atmosphere. SO2 is a distinctive marker for volcanic ash clouds, a hazard to aircraft.

[1] The altitude of volcanic sulfur dioxide (SO2) plumes determines the transport and atmospheric residence time of derived sulfate aerosol, and hence their impacts on the environment and climate. Knowledge of the altitude of fresh eruption clouds is also very important in aviation safety to avoid flying through ash clouds and for forecasting of plume drift. In this paper, we demonstrate the altitude dependence of the spectral response in the backscattered ultraviolet (BUV) radiance when a SO2 absorption layer is added to an ozone-laden atmosphere. The distinctive spectral response serves as the physical basis for simultaneous SO2 loading and altitude retrievals, which can improve the characterization of volcanic emissions. We accomplish this by extending the recently developed Iterative Spectral Fitting (ISF) algorithm to include effective plume altitude determination when performing simultaneous ozone and SO2 retrievals. The extended ISF algorithm is applied to hyper-spectral Ozone Monitoring Instrument (OMI) measurements of two volcanic eruptions: Sierra Negra in October 2005 and Jebel al Tair in September 2007. The results show for the first time that a wide range of SO2 plume altitudes can be estimated directly from hyper-spectral BUV radiance measurements.

[1] Existing algorithms that use satellite measurements of solar backscattered ultraviolet (BUV) radiances to retrieve sulfur dioxide (SO2) vertical columns underestimate the large SO2 amounts encountered in fresh volcanic eruption clouds. To eliminate this underestimation we have developed a new technique, named the Iterative Spectral Fitting (ISF) algorithm, for accurate retrieval of SO2 vertical columns in the full range of volcanic emissions. The ISF algorithm is applied to Ozone Monitoring Instrument (OMI) BUV measurements of the Sierra Negra eruption (Galapagos Islands, Ecuador) in October 2005. The results represent major improvements over the operational OMI SO2 products. Based on the ISF data, we report the largest SO2 vertical column amount (>1000 Dobson Units (DU), where 1 DU = 2.69 × 1016 molecules/cm2) ever observed by a space borne instrument, implying that very high concentrations of SO2 can occur in the lower troposphere during effusive eruptions.

The Earth Observing System (EOS) scheduled for launch in 1997 and 1999 is briefly described, and the EOS volcanology investigation objectives are discussed. The volcanology investigation will include long- and short-term monitoring of selected volcanoes, the detection of precursor activity associated with unanticipated eruptions, and a detailed study of on-going eruptions. A variety of instruments on the EOS platforms will enable the study of local- and regional-scale thermal and deformational features of volcanoes, and the chemical and structural features of volcanic eruption plumes and aerosols.

The 1990 Antarctic ozone hole matched the record 1987 ozone hole in depth, duration, and area. During the formation phase of the hole (August), total ozone values were the lowest yet recorded. The decline rate approximately matched the record 1987 decline, and reached a minimum of 125 Dobson Units on October 4, 1990. October total ozone averages were marginally higher than 1987. As during 1987, the 1990 total ozone values within the hole slowly and steadily increased during the mid-October through November period. The ozone hole breakup was the latest yet recorded (early December), with low ozone values persisting over the pole through December, setting a record low for December average polar ozone. Temperatures were near average during the early spring, but were below normal for the late-spring. Temperatures in the early spring of 1990 were substantially warmer than those observed in the early spring of 1987.

The eruptions of Nevado del Ruiz in 1985 were unusually rich in sulfur dioxide. These eruptions were observed with the Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) which can quantitatively map volcanic sulfur dioxide plumes on a global scale. A small eruption, originally believed to be of phreatic origin, took place on September 11, 1985. However, substantial amounts of sulfur dioxide from this eruption were detected with TOMS on the following day. The total mass of SO 2 , approximately 9 ± 3 × 10 4 metric tons, was deposited in two clouds, one in the upper troposphere, the other possibly at 15 km near the stratosphere. The devastating November 13 eruptions were first observed with TOMS at 1150 EST on November 14. Large amounts of sulfur dioxide were found in an arc extending 1100 km from south of Ruiz northeastward to the Gulf of Venezuela and as an isolated cloud centered at 7°N on the Colombia-Venezuela border. On November 15 the plume extended over 2700 km from the Pacific Ocean off the Colombia coast to Barbados, while the isolated mass was located over the Brazil-Guyana border, approximately 1600 km due east of the volcano. Based on wind data from Panama, most of the sulfur dioxide was located at 10–16 km in the troposphere and a small amount was quite likely deposited in the stratosphere at an altitude above 24 km. The total mass of sulfur dioxide in the eruption clouds was approximately 6.6 ± 1.9 × 10 5 metric tons on November 14. When combined with quiescent sulfur dioxide emissions during this period, the ratio of sulfur dioxide to erupted magma from Ruiz was an order of magnitude greater than in the 1982 eruption of El Chichon or the 1980 eruption of Mount St. Helens.

Total ozone values measured by the Total Ozone Mapping Spectrometer during January, February, and March 1989 are analyzed. During this period, polar total ozone values did not reveal clear depletions, although average winter total ozone values indicate that a 2-6 percent ozone reduction has occurred in northern mid to high latitudes over the last 10 years. Rapid total ozone increases were seen during mid-February, resulting from a wave 2 major stratospheric warming. In order to track polar air over the warming period, total ozone trends are further analyzed using Ertel's potential vorticity.

[1] We report the first daily observations of sulfur dioxide (SO2) emissions from copper smelters by a satellite-borne sensor - the Ozone Monitoring Instrument (OMI) on NASA's EOS/Aura spacecraft. Emissions from two Peruvian smelters (La Oroya and Ilo) were detected in up to 80% of OMI overpasses between September 2004 and June 2005. SO2 production by each smelter in this period is assessed and compared with contemporaneous emissions from active volcanoes in Ecuador and southern Colombia. Annual SO2 discharge from the Ilo smelter, La Oroya smelter, and volcanoes in 2004–2005 is estimated and amounts to 0.3−0.1+0.2, 0.07 ± 0.03, and 1.2 ± 0.5 Tg, respectively. This study confirms OMI's potential as an effective tool for evaluation of anthropogenic and natural SO2 emissions. Smelter plumes transport an array of toxic metals in addition to SO2 and continued monitoring to mitigate health and environmental impacts is recommended.

Sulfate aerosol produced after injection of sulfur dioxide (SO 2 ) into the stratosphere byvolcanic eruptions can trigger climate change. We present new satellite data from theOzone Monitoring Instrument (OMI) and Cloud-Aerosol Lidar and Infrared Pathfinder 5 Satellite Observations (CALIPSO) missions that reveal the composition, structure and longevity of a stratospheric SO 2 cloud and derived sulfate layer following a modesteruption (0.2Tg total SO 2 ) of Soufriere Hills volcano, Montserrat on 20 May 2006.The SO 2 cloud alone was tracked for over 3 weeks and a distance of over 20000km;unprecedented for an eruption of this size. Derived sulfate aerosol at an altitude of ∼20 10 km had circled the globe by 22 June and remained visible in CALIPSO data until at least 6 July. These synergistic NASA A-Train observations permit a new appreciation ofthe potential effects of frequent, small-to-moderate volcanic eruptions on stratosphericcomposition and climate. 1 Introduction 15 Over the past three decades, satellite remote sensing of volcanic clouds following ma-jor explosive eruptions has delivered new insights into the magnitude of volcanic sulfurdioxide (SO

[1] In the paper ‘‘SO2 emissions from basaltic eruptions, and the excess sulfur issue’’ by Sharma et al. (Geophysical Research Letters, 31, L13612, doi:10.1029/ 2004GL019688, 2004), in paragraph [3], there is a mistake in equation (1). The authors apologize for this oversight and wish to thank Dr. Ralf Gertisser for pointing it out. [2] With this correction, equation (1) should read as follows

Volcanic SO2 can affect the Earth's environment. Where no direct measurements of SO2 in the atmosphere are available, a petrologic method of assessing sulfur release from the magma must be used. However, in studies of arc-derived eruptions, satellite-based measurements of SO2 emissions using Total Ozone Mapping Spectrometer (TOMS) data are orders of magnitude greater than those calculated petrologically, implying that a separate S-rich gas phase in the magma chamber may be responsible for the excess sulfur. We test whether this applies in other settings. For Icelandic and Hawaiian basalts we find that petrologic SO2 values are comparable to measurements of SO2 by TOMS. Thus, for non-arc basalts, the petrologic method gives reliable estimates of SO2 released. The implied absence of excess sulfur in non-arc basaltic magmas is a reflection of source magma conditions, notably lower fO2 and volatile contents than arc magmas, inhibiting the exsolution of a S-rich gas prior to eruption.

[1] A fire started at the Al-Mishraq State Sulfur plant near Mosul, Iraq on 24 June 2003 and burned for almost a month. Combustion of elemental sulfur in the fire produced dense clouds of sulfur dioxide (SO2) that were detected from space by the Earth Probe Total Ozone Mapping Spectrometer (EP TOMS) on 18 days. Estimated daily SO2 production from the continuously emitting source closely mirrors contemporaneous thermal infrared radiance from the fire sensed in the 3.96 μm band of the Moderate Resolution Imaging Spectroradiometer (MODIS). We calculate total SO2 production during the blaze amounting to ∼600 kilotons, which is roughly commensurate with the predicted SO2 yield from the inventory of elemental sulfur allegedly destroyed by the fire when potential SO2 losses are considered. This event is the largest non-volcanic SO2 emission incident measured to date by any TOMS instrument.

VOLCANIC clouds are an important natural hazard to aircraft1, and host chemical reactions that interest both volcanologists2,3 and atmospheric scientists4-6. Ice has been suggested as a possible component of eruption clouds7, but there has been no direct evidence for its presence. Here we report the detection, using a satellite-borne infrared sensor, of ≳ 2 million tonnes of ice in the cloud produced by the September 1994 eruption of Rabaul volcano, in Papua New Guinea. The cloud also contained relatively low levels of sulphur dioxide (80 ± 50 kilotonnes), compared with other stratospheric eruption clouds. The unusual aspects of this cloud may be related to the entry of sea water into the volcanic vent, and its participation in the eruption column. Past eruptions that occurred in similar (coastal) settings, such as those of Krakatau and Santorini, might have had less effect on the atmosphere than their volume alone would suggest, because the presence of ice may decrease the residence time of ash and sulphur in the atmosphere. In addition, the ability of ice to mask the characteristic spectral signature of volcanic ash will increase the difficulty of designing airborne ash detection systems for aviation safety.

OMI is an UV-Visible imaging spectrometer with the capability to measure boundary layer SO2 from space. This paper discusses the sensitivity of the OMI SO2 retrieval algorithm to different geophysical perturbations.

An 80,000 km 2 stratospheric volcanic cloud formed from the 26 February 2000 eruption of Hekla (63.98° N, 19.70° W). POAM-III profiles showed the cloud was 9-12 km asl. During 3 days this cloud drifted north. Three remote sensing algorithms (TOMS SO 2 , MODIS & TOVS 7.3 μm IR and MODIS 8.6 μm IR) estimated ∼0.2 Tg SO 2 . Sulfate aerosol in the cloud was 0.003-0.008 Tg, from MODIS IR data. MODIS and AVHRR show that cloud particles were ice. The ice mass peaked at ∼1 Tg ∼10 hours after eruption onset. A ∼0.1 Tg mass of ash was detected in the early plume. Repetitive TOVS data showed a decrease of SO 2 in the cloud from 0.2 Tg to below TOVS detection (i.e.