Total Ozone Mapping Spectrometer Instrument Research Articles

Ozone trends on equatorial and tropical regions of South America using Dobson spectrophotometer, TOMS and OMI satellites instruments

The ozone layer filters solar ultraviolet radiation and is affected by several photochemical and dynamical processes in the atmosphere. Stratospheric ozone formation takes place primarily in tropical regions and it is the consequence of reactions between atmospheric oxygen and the ultraviolet solar radiation. For the purpose of this paper, the atmospheric TOC (Total Ozone Content) measurements are calculated using Dobson spectrophotometers, in conjunction of satellite data of TOMS (Total Ozone Mapping Spectrometer), and OMI (Ozone Monitoring Instrument), at Cachoeira Paulista (22.7oS, 45.0oW) (CP) and Natal (5.8oS, 35.2oW) (NT), Brazil. The time series considered extend from 1974 to 2013 for CP and from 1978 to 2013 for NT. The mean differences in ozone values between Dobson and TOMS, and between Dobson and OMI, are about 3% and 2%, respectively. The correlations of the Dobson spectrophotometers with TOMS are inferior to the correlations of Dobson to OMI data, due to the improved retrieval and algorithm of the more recent OMI instrument. The observed long-term ozone trends obtained for CP and NT with Dobsons, are: −2.76%, for the period of 1974–2013, and -0.78%, for the period of 1978–2013, respectively. The trend in TOC per decade is of −0.71 ± 0.4% at CP, and of −0.22 ± 0.2%, at NT. The estimated seasonal trends for CP in June-July-August are −3.3%, compared to NT, which yields −1% in the same period. NT seasonal trend for December-January-February is −1.3%. This shows that there is a more significant decrease at CP than at NT, which agrees with the fact that the most active ozone production occurs near the equator. The average ozone amounts were 268.3 ± 13.1 DU for CP and 265.9 ± 10.9 DU for NT, and a seasonal cycle with a minimum of 256.0 DU at CP and NT in autumn and maximum of 283 DU at CP and 279 DU at NT in spring, of southern hemisphere.

A new discrete wavelength backscattered ultraviolet algorithm for consistent volcanic SO<sub>2</sub> retrievals from multiple satellite missions

Abstract. This paper describes a new discrete wavelength algorithm developed for retrieving volcanic sulfur dioxide (SO2) vertical column density (VCD) from UV observing satellites. The Multi-Satellite SO2 algorithm (MS_SO2) simultaneously retrieves column densities of sulfur dioxide, ozone, and Lambertian effective reflectivity (LER) and its spectral dependence. It is used operationally to process measurements from the heritage Total Ozone Mapping Spectrometer (TOMS) onboard NASA's Nimbus-7 satellite (N7/TOMS: 1978–1993) and from the current Earth Polychromatic Imaging Camera (EPIC) onboard Deep Space Climate Observatory (DSCOVR: 2015–ongoing) from the Earth–Sun Lagrange (L1) orbit. Results from MS_SO2 algorithm for several volcanic cases were assessed using the more sensitive principal component analysis (PCA) algorithm. The PCA is an operational algorithm used by NASA to retrieve SO2 from hyperspectral UV spectrometers, such as the Ozone Monitoring Instrument (OMI) onboard NASA's Earth Observing System Aura satellite and Ozone Mapping and Profiling Suite (OMPS) onboard NASA–NOAA Suomi National Polar Partnership (SNPP) satellite. For this comparative study, the PCA algorithm was modified to use the discrete wavelengths of the Nimbus-7/TOMS instrument, described in Sect. S1 of the Supplement. Our results demonstrate good agreement between the two retrievals for the largest volcanic eruptions of the satellite era, such as the 1991 Pinatubo eruption. To estimate SO2 retrieval systematic uncertainties, we use radiative transfer simulations explicitly accounting for volcanic sulfate and ash aerosols. Our results suggest that the discrete-wavelength MS_SO2 algorithm, although less sensitive than hyperspectral PCA algorithm, can be adapted to retrieve volcanic SO2 VCDs from contemporary hyperspectral UV instruments, such as OMI and OMPS, to create consistent, multi-satellite, long-term volcanic SO2 climate data records.

Measurements of the total ozone column using a Brewer spectrophotometer and TOMS and OMI satellite instruments over the Southern Space Observatory in Brazil

Abstract. This paper presents 23 years (1992–2014) of quasi-continuous measurements of the total ozone column (TOC) over the Southern Space Observatory (SSO) in São Martinho da Serra, Brazil (29.26° S, 53.48° and 488 m altitude). The TOC was measured by a Brewer spectrometer, and the results are also compared to daily and monthly observations from the TOMS (Total Ozone Mapping Spectrometer) and OMI (Ozone Monitoring Instrument) satellite instruments. Analyses of the main interannual modes of variability computed using the wavelet transform method were performed. A favorable agreement between the Brewer spectrophotometer and satellite datasets was found. The seasonal TOC variation is dominated by an annual cycle, with a minimum of approximately 260 DU in April and a maximum of approximately 295 DU in September. The wavelet analysis applied in the SSO TOC anomaly time series revealed that the Quasi-Biennial Oscillation (QBO) modulation was the main mode of interannual variability. The comparison between the SSO TOC anomaly time series with the QBO index revealed that the two are in opposite phases.

Analysis of Ozone (O3) and Erythemal UV (EUV) measured by TOMS in the equatorial African belt

We presented time series of total ozone column amounts (TOCAs) and erythemal UV (EUV) doses derived from measurements by TOMS (Total Ozone Mapping Spectrometer) instruments on board the Nimbus-7 (N7) and the Earth Probe (EP) satellites for three locations within the equatorial African belt for the period 1979 to 2000. The locations were Dar-es-Salaam (6.8° S, 39.26° E) in Tanzania, Kampala (0.19° N, 32.34° E) in Uganda, and Serrekunda (13.28° N, 16.34° W) in Gambia. Equatorial Africa has high levels of UV radiation, and because ozone shields UV radiation from reaching the Earth’s surface, there is a need to monitor TOCAs and EUV doses. In this paper we investigated the trend of TOCAs and EUV doses, the effects of annual and solar cycles on TOCAs, as well as the link between lightning and ozone production in the equatorial African belt. We also compared clear-sky simulated EUV doses with the corresponding EUV doses derived from TOMS measurements. The TOCAs were found to vary in the ranges 243 DU − 289 DU, 231 DU − 286 DU, and 236 DU − 296 DU, with mean values of 266.9 DU, 260.9 DU, and 267.8 DU for Dar-es-Salaam, Kampala and Serrekunda, respectively. Daily TOCA time series indicated that Kampala had the lowest TOCA values, which we attributed to the altitude effect. There were two annual ozone peaks in Dar-es-Salaam and Kampala, and one annual ozone peak in Serrekunda. The yearly TOCA averages showed an oscillation within a five-year period. We also found that the EUV doses were stable at all three locations for the period 1979−2000, and that Kampala and Dar-es-Salaam were mostly cloudy throughout the year, whereas Serrekunda was mostly free from clouds. It was also found that clouds were among the major factors determining the level of EUV reaching the Earth´s surface. Finally, we noted that during rainy seasons, horizontal advection effects augmented by lightning activity may be responsible for enhanced ozone production in the tropics.

El Chichon: The genesis of volcanic sulfur dioxide monitoring from space

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.

Aerosol variability over Thessaloniki using ground based remote sensing observations and the TOMS aerosol index

The main aim of this work is to assess the performance of the Total Ozone Mapping Spectrometer (TOMS) on board the Earth Probe satellite aerosol index (AI) version 8.0 retrieved from the daily measurements of the TOMS instrument as an indicator of the presence of absorbing aerosols in the atmosphere. The analysis is carried out over the region of Northern Greece, an area exposed to various aerosol types from different sources. The aerosol optical depth (AOD) measured by a Brewer spectroradiometer situated in the centre of the city of Thessaloniki, at 40.6°N, 22.9°E, was employed as a measure of the aerosol loading in the atmosphere during the Earth Probe overpass. Discrete aerosol episodes that affect the area, such as biomass burning and Saharan dust events, have been isolated and studied in order to assess the effectiveness of using the TOMS AI in this highly complex atmospheric environment. The yearly values for the AOD measured at 355 nm range from 0.03 to 1.97 with a mean of 0.58±0.32 and for the AI from −1.67 to 3.06, with a mean of 0.22±0.73. This wide range of values results from the co-existence of urban, continental, marine and dust aerosols over Thessaloniki, a fact that makes it complicated to segregate optical effects on the observed radiation depending on different aerosol types. A total of 223 biomass burning events that affected Thessaloniki showed a correlation of 0.67 between the AOD and AI values whereas a correlation of 0.57 was deduced for the 37 cases of Saharan dust loading. A cluster analysis on the back-trajectories was performed in order to study the origins of the air masses over Thessaloniki, which permitted that the optical depth and AI were analysed depending on the possible source of the aerosols. The highest AOD values coupled with the highest AI values were seen for trajectories that transport air from the Saharan desert over Thessaloniki and those that bring polluted air from Eastern Europe and the Balkan regions. Even though some deductions were made vis-à-vis the origin and importance of different aerosol types over the city corroborating the usefulness of the AI in climatological or global climate studies, auxiliary information is essential for studying in detail the effects of the atmospheric aerosol loading over a local point of interest.

Synoptic-Scale Variability and Its Relationship with Total Ozone and Antarctic Vortex Displacements

Abstract The main synoptic-scale circulation anomaly pattern over extratropical South America during the austral spring (September–November) is identified by means of rotated extended empirical orthogonal function techniques, applied to the meridional wind perturbation time series at 300 hPa. The dataset is based on 15 spring seasons (1979–93) of meteorological data from the National Centers for Environmental Prediction–Department of Energy Atmospheric Model Intercomparison Project version-2 daily averaged reanalyses, given in 17 vertical levels from 1000 to 10 hPa. The total-ozone daily measurements for the same period are from the Total Ozone Mapping Spectrometer instrument (version 7). The principal synoptic-scale anomaly pattern is associated with an anticyclone–cyclone pair evolving eastward along subpolar latitudes (and hence it is termed the subpolar mode), with a typical length scale of 5000 km and a phase velocity of 8 m s−1. The subpolar-mode waves, which display the main characteristics of midlatitude baroclinic waves, typically maximize near or above the tropopause and propagate upward into the lower stratosphere, showing large amplitudes even at 50 hPa and above. Subpolar-mode-related circulation anomalies are found to be responsible for large total-ozone daily fluctuations near southern South America and nearby regions. In the positive phase of the subpolar mode, total-ozone fluctuations, which are negative, adopt a sigmoid structure, with a zonal scale as large as the anticyclone–cyclone pair. Moreover, it is herein shown that the associated anticyclone produces a local ozone-column decrease to the north and east of its center, due to adiabatic uplift of air parcels in the upper troposphere and lower stratosphere. At the same time, the downstream cyclonic disturbance is responsible for large negative total-ozone anomalies to the west and south of its center. As the cyclone develops in the lower stratosphere, it promotes the northward incursion of the Antarctic vortex up to about 55°S, along with air masses of highly depleted ozone levels.

Spatial Statistics in the Presence of Location Error with an Application to Remote Sensing of the Environment

Techniques for the analysis of spatial data have, to date, tended to ignore any effect caused by error in specifying the spatial locations at which measurements are recorded. This paper reviews the methods for adjusting spatial inference in the presence of data-location error, particularly for data that have a continuous spatial index (geostatistical data). New kriging equations are developed and evaluated based on a simulation experiment. They are also applied to remote-sensing data from the Total Ozone Mapping Spectrometer instrument on the Nimbus-7 satellite, where the location error is caused by assignment of the data to their nearest grid-cell centers. The remote-sensing data measure total column ozone (TCO), which is important for protecting the Earth's surface from ultraviolet and other radiation.

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

Abstract Since their first depolyment in November 1978, the Total Ozone Mapping Spectrometer (TOMS) instruments have provided a robust and near-continuous record of sulphur dioxide (SO 2 ) and ash emissions from active volcanoes worldwide. Data from the four TOMS satellites that have flown to date have been analysed with the latest SO 2 /ash algorithms and incorporated into a TOMS volcanic emissions database that presently covers 22 years of SO 2 and ash emissions. The 1978–2001 record comprises 102 eruptions from 61 volcanoes, resulting in 784 days of volcanic cloud observations. Regular eruptions of Nyamuragira (DR Congo) since 1978, accompanied by copious SO 2 production, have contributed material on approximately 30% of the days on which clouds were observed. The latest SO 2 retrieval results from Earth Probe (EP) TOMS document a period (1996–2001) lacking large explosive eruptions, and also dominated by SO 2 emission from four eruptions of Nyamuragira. EP TOMS has detected the SO 2 and ash produced during 23 eruptions from 15 volcanoes to date, with volcanic clouds observed on 158 days. The EP TOMS instrument began to degrade in 2001, but has now stabilized, although its planned successor (QuikTOMS) recently failed to achieve orbit. New SO 2 algorithms are currently being developed for the Ozone Monitoring Instrument, which will continue the TOMS record of UV remote sensing of volcanic emissions from 2004 onwards.

Impact of ozone mini-holes on the heterogeneous destruction of stratospheric ozone.

A comprehensive study of ozone mini-holes over the mid-latitudes of both hemispheres is presented, based on model simulations with the coupled climate-chemistry model ECHAM4.L39(DLR)/CHEM representing atmospheric conditions in 1960, 1980, 1990 and 2015. Ozone mini-holes are synoptic-scale regions of strongly reduced total ozone, directly associated with tropospheric weather systems. Mini-holes are supposed to have chemical and dynamical impacts on ozone levels. Since ozone levels over northern mid-latitudes show a negative trend of approximately -4%/decade and since it exists a negative correlation between total column ozone and erythemally active solar UV-radiation reaching the surface it is important to understand and assess the processes leading to the observed ozone decline. The simulated mini-hole events are validated with a mini-hole climatology based on daily ozone measurements with the TOMS (total ozone mapping spectrometer) instrument on the satellite Nimbus-7 between 1979 and 1993. Furthermore, possible trends in the event frequency and intensity over the simulation period are assessed. In the northern hemisphere the number of mini-hole events in early winter decreases between 1960 and 1990 and increases towards 2015. In the southern hemisphere a positive trend in mini-hole event frequency is detected between 1960 and 2015 in spring associated with the increasing Antarctic Ozone Hole. Finally, the impact of mini-holes on the stratospheric heterogeneous ozone chemistry is investigated. For this purpose, a computer-based detection routine for mini-holes was developed for the use in ECHAM4.L39(DLR)/CHEM. This method prevents polar stratospheric cloud formation and therefore heterogeneous ozone depletion inside mini-holes. Heterogeneous processes inside mini-holes amount to one third of heterogeneous ozone destruction in general over northern mid- and high-latitudes during winter (January-April) in the simulation.

Assimilation of ozone profiles and total column measurements into a global general circulation model

Ozone profiles from the Microwave Limb Sounder (MLS) instrument flown on board the Upper Atmosphere Research Satellite (UARS) and total ozone columns measured by the Global Ozone Monitoring Experiment (GOME) on board the Second European Remote Sensing Satellite (ERS‐2) have been assimilated using a troposphere‐stratosphere data assimilation system. The analysis system is based on the global analysis system used for operational analysis of the stratosphere at the Meteorological Office from 1991 to 2000. Three assimilation runs have been completed for a three‐week period in April 1997 to test the advantage of using a combination of MLS and GOME observations, compared with the assimilation of each observation data set separately. The statistical information produced by the assimilation system shows that the combination of MLS and GOME observations via the assimilation process produces ozone fields that show improvement compared with analysis fields produced by the assimilation of either MLS or GOME separately. Comparison of the analyzed ozone fields with independent observations (ozonesondes, Halogen Occultation Experiment (HALOE) profiles and Total Ozone Mapping Spectrometer (TOMS) total ozone column measurements) corroborates these results and shows that the combined MLS and GOME ozone analyses provide a realistic representation of the atmospheric ozone distribution. The global root‐mean‐square residual (difference between the analyses and independent observations) against HALOE and TOMS observations is comparable to the quoted errors in the HALOE and TOMS instruments (5% in each case).

The sensitivity of tropospheric methane to the interannual variability in stratospheric ozone

The dominant processes affecting the concentration of tropospheric methane on interannual timescales are the biospheric and anthropogenic sources and changes in the abundance of the hydroxyl radical caused by the changes in the UV flux which result from changes in stratospheric ozone abundance. We have carried out an empirical study of the sensitivity of the methane to fluctuations in ozone column abundance. This analysis was carried out using monthly mean surface methane concentrations measured by the National Oceanic and Atmospheric Administration – Climate Monitoring and Diagnostics Laboratory (NOAA-CMDL) Global Cooperative Air Sampling Network from 1983 to 1998 and ozone column abundances obtained by the Total Ozone Mapping Spectrometer (TOMS) and the EP TOMS instruments over the same time period. We focused on interannual variability with periods between 15 and 60 months, in which interval the dominant ozone fluctuation is the quasi-biennial oscillation (QBO), with a period of approximately 29 months. In order to isolate the response of methane to ozone from the effects of variability in the sources and transport of methane, we restricted our analysis to data at mid-latitudes in the southern hemisphere. A statistical study shows that the sensitivity factor α≡−d(ln[CH4])/d(ln[O3])=−0.038±0.009. The response of CH4 lags approximately 6 months behind the forcing by O3. A simple model was used to interpret the empirical results. Our results confirm that any mechanism that affects stratospheric ozone impacts the oxidizing potential of the troposphere. CH4 fluctuations provide a quantitative measure of this important effect linking the upper and the lower atmosphere.

Erythemal Weighted Ultraviolet Trends Over Northern Latitudes

This study examines the distribution of long-term trends in ground-level erythemally-weighted ultraviolet-B (UVB, wavelengths 290-320 nm) exposures in the northern latitudes for the period 1979-1991 using measurements from the Nimbus 7 total ozone mapping spectrometer instrument. Zonal mean erythemal UV data show ~3-7% per decade increases in the mid-to-high latitudes. Analysis of the horizontal patterns in trends around summer months indicates that most of the regional increases (exceeding 6% per decade) in the northern hemisphere in the latitude range 30o - 40oN originate from the Pacific and Atlantic oceanic regions. Increases (also exceeding 6% per decade) in latitudes 40o - 60o appear to originate from the North American and Asian continents and also central Europe. Trends over the east Asian continent in high latitudes indicate increases exceeding 10% per decade for May-August.

Fine‐scale comparison of TOMS total ozone data with model analysis of an intense Midwestern cyclone

High‐resolution (∼40 km) along‐track total column ozone data from the Total Ozone Mapping Spectrometer (TOMS) instrument are compared with a high‐resolution mesoscale numerical model analysis of an intense cyclone in the Midwestern United States. Total ozone increased by ∼100 DU (nearly 38%) as the TOMS instrument passed over the associated tropopause fold region. Complex structure is seen in the meteorological fields and compares well with the total ozone observations. Ozone data support the meteorological analysis showing that stratospheric descent was confined to levels above ∼600 hPa; significant positive potential vorticity at lower levels is attributable to diabatic processes. Likewise, meteorological fields show that two pronounced ozone streamers extending north and northeastward into Canada at high levels are not bands of stratospheric air feeding into the cyclone; one is a channel of exhaust downstream from the system, and the other apparently previously connected the main cyclonic circulation to a southward intrusion of polar stratospheric air and advected eastward as the cut‐off cyclone evolved. Good agreement between small‐scale features in the model output and total ozone data underscores the latter's potential usefulness in diagnosing upper‐tropospheric/lower‐stratospheric dynamics and kinematics.

Statistical characteristics of total ozone measurements by the Total Ozone Mapping Spectrometer

An attempt is made to study the accuracy and the precision of the total ozone data observed by the Total Ozone Mapping Spectrometer (TOMS) on board Nimbus 7 and Meteor 3 satellites. Two TOMS instruments have shown statistically significant mean bias at 5% level. Averaged total ozone contours sometimes coincide with coast lines indicating some problem in the treatment of surface albedo. Systematic errors are noticed in TOMS data especially in the tropics. By using the ground-based Dobson data, such errors are identified as those being correlated to the errors at other locations. The estimated variances are 5–10 DU 2 for random errors in the Dobson data, 2–3 DU 2 for random errors and 10 DU 2 for systematic errors in the TOMS data in the tropics.

TOMS/ADEOS instrument characterization

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%.

Total ozone series at Arosa (Switzerland): Homogenization and data comparison

Five Dobson and two Brewer spectrophotometers were used for total ozone observations at Arosa, beginning in 1926 and providing the world's longest series. In this paper we present the results of our attempts to provide a homogeneous series and discuss the data quality problems of the record. From the mid‐1950s to 1992, Dobson instrument D15 was calibrated by the statistical Langley plot method. In 1986 the calibration of another Dobson spectrometer at Arosa (D101) was changed by the intercomparison with the primary world Dobson instrument (D83). A statistical model based on simultaneous measurements of D101 and D15 of the period from 1987 to 1990 was used to obtain a total ozone series in line with the primary Dobson spectrophotometer, including a correction for an optical disalignment problem of D15. The series of Dl0l from 1990 to 1995 was corrected on the basis of data from the Dobson intercomparisons of 1990 and 1995 and comparisons with other total ozone measurements of Brewer and Dobson spectrophotometers at Arosa. A transfer function between Dobson and Brewer spectrophotometric measurements of Arosa is presented, and total ozone measurements of Arosa are compared with version 7 daily overpass data of the satellite instrument the total ozone mapping spectrometer (TOMS) which operated on board Nimbus 7 from autumn 1978 to spring 1993. Available information allowing us to track back the total ozone measurements of Arosa to the measurements of the primary Dobson spectrometer reveal that the total ozone series of Arosa fluctuated no more than approximately 1% against D83 in the period from 1978 to 1995. Average shift of Arosa total ozone data against the TOMS instrument was −1.12 (±0.1)% over the lifetime of the TOMS instrument.

New TOMS instrument measures ozone and aerosols

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.

Total ozone/UVB monitoring and forecasting: Impact of clouds and the horizontal resolution of satellite retrievals

This study compares the horizontal resolution of solar backscatter ultraviolet 2 (SBUV2) total ozone (Ω) fields with those from the new NASA earth probe (EP) and Advanced Earth Observing Satellite (ADEOS) total ozone mapping spectrometer (TOMS) side‐scanning photometers. The latter instruments provide high resolution, easily resolving the medium‐scale waves (4–7 wavelengths around the Earth at a fixed latitude) that dominate day‐to‐day midlatitude Ω fluctuations. In contrast, SBUV2 instruments do not, since these devices measure only at nadir (straight downward), yielding ∼14 measurements daily at a given latitude. This method has consequences not only for global monitoring of Ω and ultraviolet B (UVB, 290–320 nm), but also for short‐timescale Ω and UVB predictions in summer because timescales of a few days are coupled to medium horizontal scales (several thousand kilometers) by baroclinic waves that typically force the observed Ω variations. We use a simple Ω prediction model to test the use of Ω fields from TOMS and SBUV instruments and show that the higher zonal resolution from side‐scanning TOMS instruments results in sizeable reductions in Ω prediction errors, whereas predictions using SBUV2 Ω are no better than persistence (where tomorrow's Ω is taken to be today's) in the biologically important summer months. Daily variabilities (equivalent to errors in 24‐hour persistence forecasting of Ω) in high‐resolution TOMS midlatitude ozone during summer are shown to sometimes exceed 50 Dobson units, producing daily changes of 20% or greater in computed ground‐level clear‐sky UV index. This study demonstrates that even these large daily changes in measured or predicted clear‐sky UV are usually smaller than daily UV changes associated with transient clouds. While surface UVB variability is dominated by local cloudiness variations, Ω forecasts can enhance UVB prediction in relatively cloud free regions such as the U.S. desert southwest and in stagnant high‐pressure regimes that can persist for 1–2 weeks in summer. Furthermore, as weather forecast models increase in accuracy of forecasted cloudiness, accurate predictions will allow more accurate UVB forecasts for cloud free regions, the locations where they are most needed. Results from the present paper show, however, that high‐resolution TOMS‐like side‐scanning Ω measurements are required for ozone and UVB monitoring and prediction, rather than SBUV‐type nadir observations.

Detection of biomass burning smoke from TOMS measurements

A 14.5 year gridded data set of tropospheric absorbing aerosol index was derived from the Nimbus‐7 Total Ozone Mapping Spectrometer (TOMS) reflectivity difference between 340 and 380 nm channels. Based upon radiative transfer calculations, the reflectivity anomaly between these two UV wavelength channels is very sensitive to smoke and soot aerosols from biomass burning and forest fires, volcanic ash clouds as well as desert mineral dust. We demonstrate the ability of the TOMS instrument to detect and track smoke and soot aerosols generated by biomass burning in South America. TOMS data can clearly distinguish between absorbing particles (smoke and dust) and non‐absorbing aerosols (clouds and haze). For South American fires, comparisons of TOMS data are consistent with the limited amount of ground‐based observations (Porto Nacional, Brazil) and show generally good agreement with other satellite imagery. TOMS data shows large‐scale transport of smoke particulates generated by the burning fires in the South America, which subsequentially advects smoke aerosols as far as the Atlantic Ocean east of Uruguay.