Search

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.

Sulfur dioxide is emitted by volcanoes, produced by combustion of fossil fuels or smelting of ores, and is an intermediate product from organic sources in the ocean. It is rapidly oxidized to sulfuric acid, which causes acidic pollution of lakes and streams and forms an aerosol that is important in climate change. Volcanic sulfur dioxide is a useful marker for ash clouds that are a hazard to aircraft. Satellites offer the best platform to monitor SO2 sources and to track volcanic clouds. UV remote sensing instruments have measured eruption plume masses since 1978. Newer instruments are sensitive enough to also measure volcanic degassing, emissions from power plants, refineries, smelters, and heavy air pollution episodes. New retrieval algorithms have improved the data quality. The observations are used to constrain models of eruption processes and to monitor activity of all volcanoes in a consistent manner. The practical applications of the satellite data include aviation safety, air quality, environmental control, climate modeling, and atmospheric dynamics modeling.

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.

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...

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).

Data sets from the total ozone mapping spectrometer (TOMS) on the ADEOS I spacecraft have been processed using initial and time-dependent instrument characterizations. Initial characterizations, performed on the ground, focused on wavelength registration of the six near-UV TOMS channels and on the instrument albedo calibration. Few calibration adjustments were required in the postlaunch phase. Instrument performance, including bandpass wavelengths, were stable throughout the life of the instrument. Indirect evidence exists for small changes in the reflectance of the primary solar diffuser. Characterizations used in data processing assume no change. No ozone retrieval errors are expected due to this assumption. All totaled, estimated calibration uncertainties represent less than 1% in total column ozone uncertainty. A comparison between two TOMS instruments is marginally consistent with these estimates. However, a comparison with ground measurements resulted in differences exceeding 1%.

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.

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.

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

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.

[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 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.

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.

SULPHUR dioxide from volcanic eruptions may have a significant effect on the Earth's climate and atmospheric chemistry, and it is therefore important to quantify outgassing rates for all types of volcanic activity. Non-explosive volcanoes (for example, Mount Etna) outgas at relatively constant rates, providing an annual flux of about 9 million tons (Mt) SO2 (ref. 1). By contrast, the outgassing from volcanoes prone to explosive eruptions (such as Mount Pinatubo) is sporadic and much more difficult to quantify. The total annual volcanic SO2 flux is therefore poorly constrained, with ground-based estimates1–8 ranging from 1.5 to 50 Mt–up to onequarter of the estimated current anthropogenic contribution. The Total Ozone Mapping Spectrometer aboard the NASA satellite Nimbus 7 recorded SO2emissions from explosive eruptions from November 1978 to May 1993. We use these data to show that the annual flux from explosive volcanism is of the order of 4 Mt SO2, less than half of the non-explosive output. Thus it seems that the total volcanic emission of SO2 to the Earth's atmosphere is about 13 Mt yr−1, which is only 5–10% of the current anthropogenic flux.

New Total Ozone Mapping Spectrometer (TOMS) instruments launched in 1996 have provided new and better information about ozone distribution, sulfur dioxide concentrations following large volcanic eruptions, the distributions of ultraviolet-absorbing aerosols (including ash plumes) in the troposphere, and the flux of ultraviolet radiation reaching the Earth's surface. The instruments gathered important data on ozone depletion in the Antarctic in the austral springs of 1996 and 1997 and in the Arctic in the Northern Hemisphere spring of 1997. Ash clouds associated with forest fires in the United States and in Indonesia, as well as the eruption of the Soufriere Hills volcano in Montserrat in December 1997, were also observed. NASA's Earth Probe (EP) satellite, launched in July 1996, carries one TOMS instrument. A second TOMS instrument flew on the Japanese Advanced Environmental Orbiting Satellite (ADEOS), known as “Midori,” launched in August 1996 from Japan. Unfortunately, because the ADEOS spacecraft failed in June 1997, only 10 months of data are available from the ADEOS TOMS instrument (see http://mentor.eorc.nasda.go.jp/ADEOS). The Earth Probe satellite flew in a 500 km Sun-synchronous orbit, which was chosen to complement the 800 km altitude of the ADEOS spacecraft by providing improved horizontal resolution for viewing aerosol sources (26 km x 26 km at nadir instead of the 42 km x 42 km resolution of ADEOS). Because of the lower orbit, data gaps did not allow for full daily maps of the sunlit Earth from EP TOMS. In order to restore the complete global coverage lost with the ADEOS failure, the EP spacecraft was boosted to a 740 km orbit in early December 1997.

The Cerro Hudson volcano in southern Chile (45.92°S, 73.0°W) emitted large ash and sulfur dioxide clouds on August 12–15, following several days of minor activity [Global Volcanism Network Bulletin, 1991]. The SO2 clouds were observed using (preliminary) near real-time data from the Total Ozone Mapping Spectrometer (TOMS) as they encircled the south polar region. The injection of SO2 into the stratosphere has essentially created a gigantic chemical tracer that could provide new insights into the wind patterns and seasonal circulation around the Antarctic region. around the Antarctic region. The TOMS instrument, on board the National Aeronautic and Space Administration's Nimbus 7 satellite, measures the ratio of backscattered Earth radiance to incoming solar irradiance in the ultraviolet spectrum. Although originally designed to measure ozone, it was later discovered that the TOMS instrument could also detect and quantify SO2 [Krueger, 1985]. After this discovery, measurements from TOMS were examined for SO2 emissions for all recorded volcanic eruptions since Nimbus-7 was launched in October 1978, and current data are analyzed as new eruptions occur. The satellite is in a polar, Sun-synchronous orbit so that it crosses the equator at local noon and observes the whole sunlit Earth in approximately 14 orbits each day. Total column amounts of SO2 are determined that represent the amount of gas affecting the reflection of ultraviolet light through a column of the atmosphere from the satellite to the reflecting surface, Earth, given in terms of milli atmospheres centimeter (1000 milli atm cm = a gas layer 1-cm thick at STP). The mass of SO2 is calculated by integrating over the cloud area to obtain a volume, then converting to tons.

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 (NO(x)) produced by the event.

A more detailed examination of the TOMS observations reveals a number of important aspects of the Antarctic ozone depletion. First, it is noted that the presence of large scale disturbances around the edge of the ozone hole can lead to highly variable station observations. Second, an examination of the zonal mean total ozone for the seven Octobers shows that the large systematic decline is not simply confined to the polar region but exists at midlatitudes as well. Integrations of the total ozone from the South Pole northwards show that a portion of the systematic trend of decreasing Antarctic total ozone (prior to 1985) seems to be due to a redistribution of total ozone to subpolar and midlatitude regions. That is, decreases at high latitudes are compensated by increases at lower latitudes. The correlation between zonal mean total ozone and 70 mb zonal mean temperatures from polar to midlatitudes shows that the systematic decreases in total ozone is well correlated with a systematic decrease in stratospheric temperatures.

Farman et al.1 have reported a rapid decrease, since their measurements started in 1957, of the total column amount of ozone in late winter and early spring over the Halley Bay station in Antarctica (76° S, 27° W). The decrease was most pronounced in October, early spring in the Southern Hemisphere. They attributed the decrease to the increase in stratospheric chlorine due to chloro-fluorocarbon release, and proposed that the unique conditions of extreme cold and low sunlight in the Antarctic winter and spring enhanced the effect. We report measurements from the Solar Backscatter Ultraviolet (SBUV) instrument and the Total Ozone Mapping Spectrometer (TOMS) aboard the Nimbus 7 satellite, a Sun-synchronous polar-orbiting satellite which passes any given point on the dayside near local noon. These provide global measurements of ozone from November 1978 to the present which confirm the reported decline of total ozone and show the phenomenon to be regional in extent. The decrease occurs during September as the Sun rises, reaching a minimum in mid-October. Seven years (1979–1985) of October monthly means show a 40% decrease in the ozone minimum and a 20% decrease in the surrounding ozone maximum.

In 1987 the Antarctic springtime total ozone as measured by TOMS was substantially lower than in any previous year. Polar ozone levels began decreasing significantly after a mesoscale transient minimum developed over the Weddell Sea on September 5-7. The total ozone over most of the Antarctic continent decreased to less than 200 DU on September 19, and a region where total ozone was less than 125 DU developed on September 30. The lowest level observed was 109 DU on October 5 near the South Pole, a value 29 DU less than the 1985 previous record low. Compared with previous years the 1987 October zonal mean total ozone is substantially lower poleward of 60 S. Antarctic total ozone in 1987 also showed the greatest rate of ozone decrease as well as the longest persistence of the ozone hole.

The 1988 spring Antarctic ozone depletion was observed by TOMS to be substantially smaller than in recent years. The minimum polar total ozone values declined only 15 percent during September 1988, compared to nearly 50 percent during September 1987. At southern midlatitudes, exceptionally high total ozone values were recorded beginning in July 1988. The total integrated southern hemispheric ozone increased rapidly during the Austral spring, approaching 1980 levels during October. The high midlatitude total ozone values were associated with a substantial increase in eddy activity as indicated by the standard deviation in total ozone in the zonal band 30-60 deg S. Mechanisms through which the increased midlatitude eddy activity could disrupt the formation of the Antarctic ozone hole are briefly discussed.

Analyses of research aircraft observation, satellite total columnar ozone retrievals and synoptic upper-air soundings are used to describe the structure of Arctic jetstreams and their associated frontal zones and tropopause folds. These analyses document the presence of major tropopause folding events within the Arctic that occur at the flanks of large-scale (∼2000 km) polar vortices. One example shows a polar vortex and its associated tropopause fold and Arctic front that migrated from the high Canadian Arctic southward into midlatitudes over central North America. The frigid cold-air outbreak associated with this migration was an important component in the record setting daily minimum temperatures that were recorded from the Great Lakes to southern Florida. Total columnar ozone measurements from the Total Ozone Mapping Spectrometer (TOMS) are shown to identify the location of polar vortices and the mesoscale (∼200 km) ozone gradients at the flanks of these vortices which coincide with regions o...

Global total ozone has been mapped with the Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) instrument since November 1978. Very detailed daily maps are produced with this instrument which has a spatial resolution at nadir of 50km. The data accuracy is better than 2% under all weather conditions as evaluated by comparison with Dobson spectrophotometer network stations. Coverage is complete at all sunlit latitudes including the poles during non-polar night months. The general structure of southern hemisphere total ozone is a polar minimum surrounded by a circumpolar maximum. Over much of the year the gradients are quite small except for local midlatitude storms. However, during the spring months the difference between the minimum and the maximum grows with time. The boundary of the polar minimum is generally very sharp with a gradient of 10 Dobson units/100km not uncommon, thus justifying the term "ozone hole" to describe this feature. A station in the boundary region will undergo very large changes in ozone as the position of the hole drifts and fluctuates. Finally, the ozone hole is destroyed as the polar vortex breaks down in November. These characteristics were illustrated during the Symposium in a motion picture of daily ozone maps for a complete year. A second motion picture shows the striking decrease of Antarctic ozone during each of the October months since 1979 to values near 140 Dobson units, far below the lowest (180 Dobson units) ever observed previously at any location. It is this decrease which is the subject of the current controversy over possible fluorocarbon effects on ozone. The data from TOMS show that dynamics are critical in the formation of the ozone hole. Total ozone in the Antarctic region is found to be highly correlated with air temperature in the lower stratosphere.

Three classes of ozone sounders have been developed since the first Echo Satellite measurements in 1960. They are the (1) backscatter ultraviolet (b.u.v.), (2) infrared limb and nadir radiance, and (3) stellar and solar occultation methods. With these techniques, ozone has been measured from 20 to 100 km. Tropospheric ozone measurements are beyond present technology, bu t total ozone is determined with the b.u.v. and nadir infrared methods.

Total ozone measurements by the Total Ozone Mapping Spectrometer (TOMS) aboard the Nimbus 7 satellite show the reappearance in 1986 of the extreme springtime Antarctic ozone minimum during September and October.The minimum total ozone amounts descended to 156 Dobson Units; the minimum October average of 185 DU was 27 DU higher than the corresponding average in 1985 and 5 DU less than the 1984 average. This behavior indicates a pause in the downward trend of recent years.

The ultraviolet earth radiance data from the Backscatter Ultraviolet Experiment on Nimbus 4 have been inverted to infer ozone profiles using a single Rayleigh scattering model. Two methods of solution give essentially the same results. Comparisons of these profiles with simultaneous rocket sounding data shows satisfactory agreement at low and middle latitudes. Vertical cross sections of ozone mixing ratio along the orbital tracks indicate that while the gross characteristics of the ozone field above 10 mb are under photochemical control, the influence of atmospheric motions can be found up to the 4 mb level.

Total ozone is estimated from Nimbus IV satellite measurements of the attenuation of backscattered radiances at wavelengths between 3100 and 3400 A. A measurement of the backscattered radiance at 3800 A, outside the O3 absorption band, is used to determine an equivalent Lambert albedo for the cloud-ground-haze surface viewed by the instrument. The measured relative attenuation at two wavelengths is compared with such values pre-computed for a series of standard O3 profiles and corrected for the equivalent Lambert

Rocket-borne radiometer determinations of ozone distributions by absorption of ultraviolet sunlight show anomalous eflects near 3000 angstroms. The instrument uses four 40-angstrom filters in the spectral region between 2650 and 3300 angstroms. At altitudes below 40 kilometers, signals from filters centered near 3000 angstroms appear reduced at least 25 percent below calculated values. However, at higher altitudes an unpredicted sharp increase in signals is observed. These effects are inconsistent with ozone absorption and cannot be ascribed to instrument characteristics. A previously unobserved absorption band of an atmospheric constituent, possibly the metastable excited states of molecular oxygen O(2)((1)Delta(g)) or O(2)((1)Sigma(g)+) can account for the anomalous effects.

On presente les grandes lignes des scenarios des variations de l'ozone: activite solaire, pollution, eruption volcanique, redistribution de la circulation atmospherique