Earth Probe Total Ozone Mapping Spectrometer Research Articles

The Empirically Corrected EP-TOMS Total Ozone Data Against Brewer Measurements at El Arenosillo (Southwestern Spain)

This paper focuses on the validation of the empirically corrected total ozone column (TOC) data provided by the Earth Probe Total Ozone Mapping Spectrometer (EP-TOMS) using ground-based measurements recorded by a well-calibrated Brewer spectroradiometer located at El Arenosillo (Spain). In addition, satellite TOC observations derived from the Ozone Monitoring Instrument (OMI) with the TOMS algorithm are also used in this paper. The agreement between EP-TOMS TOC data and Brewer measurements is excellent (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ~ 0.92) even for the period 2000-2005 when a higher EP-TOMS instrument degradation occurred. Despite its low magnitude, the EP-TOMS-Brewer relative differences depend on the solar zenith angle (SZA), showing a clear seasonal cycle with amplitude between ±2% and ±4%. Conversely, OMI-Brewer relative differences show a constant negative value around -1% with no significant dependence on SZA. No significant dependence on the ground-based to satellite-based differences with respect to the EP-TOMS scene or to the OMI crosstrack position is observed for either satellite retrieval algorithm. Finally, TOC, estimated by the two satellite instruments, have also been compared, showing a good agreement (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ~ 0.88). Overall, we conclude that the empirical correction of the EP-TOMS data record provides a reprocessed set of high quality. However, EP-TOMS data after year 2000 should not be used in calculations of global-ozone trending due to remaining errors in the data set and because it is no longer an independent data set.

A new ENSO index derived from satellite measurements of column ozone

Abstract. Column Ozone measured in tropical latitudes from Nimbus 7 total ozone mapping spectrometer (TOMS), Earth Probe TOMS, solar backscatter ultraviolet (SBUV), and Aura ozone monitoring instrument (OMI) are used to derive an El Nino-Southern Oscillation (ENSO) index. This index, which covers a time period from 1979 to the present, is defined as the "Ozone ENSO Index" (OEI) and is the first developed from atmospheric trace gas measurements. The OEI is constructed by first averaging monthly mean column ozone over two broad regions in the western and eastern Pacific and then taking their difference. This differencing yields a self-calibrating ENSO index which is independent of individual instrument calibration offsets and drifts in measurements over the long record. The combined Aura OMI and MLS ozone data confirm that zonal variability in total column ozone in the tropics caused by ENSO events lies almost entirely in the troposphere. As a result, the OEI can be derived directly from total column ozone instead of tropospheric column ozone. For clear-sky ozone measurements a +1 K change in Nino 3.4 index corresponds to +2.9 Dobson Unit (DU) change in the OEI, while a +1 hPa change in SOI coincides with a −1.7 DU change in the OEI. For ozone measurements under all cloud conditions these numbers are +2.4 DU and −1.4 DU, respectively. As an ENSO index based upon ozone, it is potentially useful in evaluating climate models predicting long term changes in ozone and other trace gases.

Univariate approach to the monthly total ozone time series over Kolkata, India: autoregressive integrated moving average (ARIMA) and autoregressive neural network (AR-NN) models

This study reports univariate modelling methodologies applied to the monthly total ozone concentration (TOC) over Kolkata (22°32′, 88°20′), India, derived from the measurements made by the Earth Probe Total Ozone Mapping Spectrometer (EP/TOMS). The univariate models have been generated in two forms, namely autoregressive integrated moving average (ARIMA) and autoregressive neural network (AR-NN). Three ARIMA models in the forms of ARIMA(1,1,1), ARIMA(0,1,1) and ARIMA(0,2,2) and 11 autoregressive neural network models, AR-NN(n), have been generated for a time series. Goodness of fit of the models to the time series of monthly TOC has been assessed using prediction error, Pearson correlation coefficient and Willmott's indices. After rigorous skill assessment, the ARIMA (0,2,2) has been identified as the best predictive model for the time series under study.

Response to comment on 'Impacts of aeolian dust deposition on phytoplankton dynamics in Queensland coastal waters'

In our earlier paper (Shaw et al. 2008; hereafter SGM), we related an increase in phytoplankton biomass in the coastal waters of Queensland, Australia, to the large October 2002 dust storm. Mackie (2010) has questioned these findings, stating that (i) the timing of the phytoplankton response precludes the dust storm as a causative agent for the chlorophyll (CHL) increase, and that (ii) it is not clear that there was actually any change in CHL in response to the dust storm. Mackie has highlighted that for the three regions where a CHL response was observed, the increase in CHL concentration began during the 8-day period ending on 23 October in two regions and on the 8-day period ending on 15 October in one of the regions. We agree with Mackie that these increases are not related exclusively to the large dust storm on 23 October. As stated in SGM, we believe this initial increase to be in response to smaller dust events before the major dust event. In our paper, we provided aerosol optical depth (AOD) data that supported this hypothesis. Mackie has questioned whether AOD is a reliable indicator of particulate load during the dust storm. As noted in SGM, the magnitude of the AOD value does not necessarily reflect the concentration of dust. However, AOD has been widely used in similar studies (e.g. Lenes et al. 2001; Gabric et al. 2002; Boyd et al. 2004) and we believe that, when used in conjunction with dust transport models, it is an appropriate method to indicate the presence of dust, although it does have limitations in determining dust loads. In further support of our hypothesis that there were smaller dust storms in the drought conditions before the CHL response, Australian Bureau of Meteorology (BoM) records show that therewere dust storms inwesternQueensland on 8 of the 22 days leading up to the dust storm on 23 October (BoM 2009). This activity peaked on 19 October, with an intense dust storm in the Birdsville area (reducing visibility to 300m), associated with a small low-pressure system. The red dusts from this localised event in the Simpson Desert–Channel Country would have been much more highly enriched in iron (Bullard et al. 2007) than those from the event on 23 October, which sourced dusts from a much larger area of diverse soils. Independent evidence of these events is available from the Earth Probe Total Ozone Mapping Spectrometer (EP/TOMS) aerosol data. Daily aerosol index (AI) data, calculated with the version 8 algorithm, were obtained for October 2002 from the National Aeronautics and Space Administration (NASA, http://macuv.gsfc.nasa.gov, verified 18 July 2009). TOMSAImeasurements have been used to determine the sources and distributions of aerosols and have been shown to be an effective measure of atmospheric dust loading (Israelevich et al. 2002 and references therein). EP/TOMS images of AI are shown in Fig. 1, where positive index values indicate the presence of UV-absorbing aerosols. High AI values can be seen in western Queensland on 6–8 October (Fig. 1a–c), in agreement with the BoM record that there were dust storms at this time. From these images, the region of high AI value shifts east, where moderate AI values can be seen off the Queensland coast on 8 and 9 October (Fig. 1c–d). Similarly, very high AI values were observed over central Australia during 17–20 October (Fig. 1e–h), corresponding with dust-storm records in Queensland on 17 and 19October (BoM 2009). On 20 October, high AI values were observed off the coast of Queensland and New SouthWales (Fig. 1h). Therefore, we contend that these dust storms, which occurred before themajor event on 23October, resulted in deposition of dust into Queensland coastal waters and resulted in the initial increase in phytoplankton biomass before 23 October. The second argument put forward byMackie is that the CHL concentration did not increase further following the major dust event in two of the three regions in which a response was observed and therefore it was concluded that the dust storm had no effect on phytoplankton biomass. This conclusion relates only to the intensity of the bloom and fails to acknowledge any effect that themajor dust event had on prolonging the duration of the phytoplankton response. Aperiodic phytoplankton blooms are often short-lived events where high biomass is rapidly attained in response to the addition of new nutrients (Behrenfeld et al. 1996; Cloern 1996). Nutrients are rapidly taken up by large populations of phytoplankton and are quickly depleted, causing the dissipation of the bloom. The duration of the phytoplankton CSIRO PUBLISHING

Total ozone dependence of the difference between the empirically corrected EP-TOMS and high-latitude station datasets

A comparison was made of the ground-based and satellite total ozone content (TOC) measurements in the atmosphere over the Antarctic stations Vernadsky, Halley and Amundsen–Scott and the Arctic station Barrow. A similar discrepancy analysis was performed using the global network of ground-based ozonometric stations from the beginning of regular satellite observations in 1978. Slowing of the long-term global ozone losses has been observed during the past decade and a recovery of the ozone layer is forecast for the coming decades. Therefore, the accuracy requirements for ozone measurements are increasing, which, in turn, requires corresponding analysis of the measurement errors. In this work, the Earth Probe Total Ozone Mapping Spectrometer (EP-TOMS) satellite data from 1996 to 2005 were used. Satellite daily TOC values were taken using version 8 of the algorithm introduced in 2004 and empirically corrected in 2007. The most persistent features of the relative EP-TOMS–Dobson difference are: (1) a significant increase in dispersion during the period of the spring Antarctic ozone hole and (2) a differing dependence on total ozone in the trend tendency and significance for EP-TOMS and Dobson datasets. The results indicate the influence of the specific conditions during the Antarctic ozone hole on the possible precision that could be achieved in assessments of Montreal Protocol effects in the ozone layer over this region.

Variation in atmospheric ozone concentration following strong earthquakes

The changes in atmospheric ozone concentration for earthquakes (with a magnitude greater than 5.0 on the Richter scale and a depth of focus less than 35 km), which have occurred worldwide during the period from September to March for the years 1991–2006, have been studied with the help of satellite data obtained from Nimbus‐7 Total Ozone Mapping Spectrometer (TOMS), Earth probe TOMS and the Ozone Monitoring Instrument. The trend of variation in total ozone concentration after all these earthquakes was found to be similar. The ozone concentration was low on the day of the earthquake, increased gradually after the earthquake and reached a maximum value and thereafter decreased to its normal value. The increase in ozone concentration was found to be dependent on the magnitude of the quake, depth of focus, wind direction and geographical location of the epicentre.

Predicting daily total ozone over Kolkata, India: skill assessment of different neural network models

AbstractThis paper explores the observation made by the Earth Probe Total Ozone Mapping Spectrometer (EP/TOMS) to analyse the predictability of daily total ozone concentration over Kolkata, India. Latitude, longitude, aerosol index, reflectivity, sulphur dioxide index and total ozone concentration of a given day have been used as independent variables to predict total ozone concentration of the next day. Artificial neural network in the forms of a multilayer perceptron, generalized feed forward neural network, a radial basis function network and a modular neural network have been trained to generate predictive models. Performances of the models in the test cases have been judged with the help of four statistical parameters. Finally the models have been compared with multiple linear regression and the potential of generalized feed forward neural network has been established over the other proposed models. Copyright © 2008 Royal Meteorological Society

Summertime “ozone valley” over the Tibetan Plateau derived from ozonesondes and EP/TOMS data

During the Asian summer monsoon period, total ozone over the Tibetan Plateau is much lower than that over the surrounding areas when compared at the same latitudes. This phenomenon called the “ozone valley” was investigated continuously with the use of ozonesondes and Earth Probe/Total Ozone Mapping Spectrometer (EP/TOMS). These measurements reveal that although relatively low ozone mixing ratios extend from the troposphere to the lower stratosphere, those near the tropopause (between about 150 and 70 hPa) largely contribute to lower total ozone over the Tibetan Plateau. Temperatures near the tropopause appear to be correlated with the observed ozone changes. Meteorological analyses show that this phenomenon is accompanied by the upper level monsoon anticyclone, which is characterized by deep convection over South Asia. These results suggest that lower ozone mixing ratios and colder temperatures near the tropopause are primarily due to convection, which is linked to the Asian summer monsoon.

Comparison of ground‐based Dobson and satellite EP‐TOMS total ozone measurements over Vernadsky station, Antarctica, 1996–2005

Total ozone content derived from version 8 of the Earth Probe Total Ozone Mapping Spectrometer (EP‐TOMS) satellite data was compared with that from ground‐based data obtained with the Dobson spectrophotometer no. 031 at the Ukrainian Antarctic Vernadsky station. The period of comparison is 1996–2005. The statistics for cloudy and clear sky observations are presented separately, in order to assess the influence of cloudiness on the difference between the satellite and ground‐based measurements. The main findings obtained from the TOMS–Dobson difference analysis were: (i) a significant disagreement between clear and cloudy sky differences of about 9%, which is almost the same value as in version 7; and (ii) the difference for all data equals −2.0% (2625 days), whereas in cloudless and cloudy conditions the difference is 4.1% (137 days) and −4.5% (1048 days), respectively. We conclude that the TOMS (Dobson) measurements are mostly responsible for the data disagreement in clear (cloudy) sky conditions.

Analysis of TOMS Aerosol Index and Single Scattering Albedo over the Central Indian Region

Aerosol effects are significant in processes related to the local, regional and global analysis of air pollution. Large‐scale biomass burning and forest fire events produce smoke plumes that transport smoke thousands of kilometers causing air quality and health related problems. Satellite observations provide efficient means to determine aerosol physical properties on the temporal and spatial scales needed to understand and monitor their effects on the earth‐atmosphere system. In the present study Earth Probe/Total Ozone Mapping Spectrometer (EPTOMS) data and ground‐based observations were used to study the aerosol index and single scattering albedo variation. Monthly variations in AI suggest that the concentration of UV‐absorbing aerosols gradually increases from January to May coinciding with the biomass burning activities in the region. Day average fraction of black carbon (BC) to total aerosol mass concentration is observed to be 7‐10%. The trends in satellite‐derived single scattering albedo correlate well with ground measured values.

Indicators of Antarctic ozone depletion

Abstract. An assimilated data base of total column ozone measurements from satellites has been used to generate a set of indicators describing attributes of the Antarctic ozone hole for the period 1979 to 2003, including (i) daily measures of the area over Antarctica where ozone levels are below 150 DU, below 220 DU, more than 30% below 1979 to 1981 norms, and more than 50% below 1979 to 1981 norms, (ii) the date of disappearance of 150 DU ozone values, 220 DU ozone values, values 30% below 1979 to 1981 norms, and values 50% below 1979 to 1981 norms, for each year, (iii) daily minimum total column ozone values over Antarctica, and (iv) daily values of the ozone mass deficit based on a O3&lt;220 DU threshold. The assimilated data base combines satellite-based ozone measurements from 4 Total Ozone Mapping Spectrometer (TOMS) instruments, 3 different retrievals from the Global Ozone Monitoring Experiment (GOME), and data from 4 Solar Backscatter Ultra-Violet (SBUV) instruments. Comparisons with the global ground-based Dobson spectrophotometer network are used to remove offsets and drifts between the different data sets to produce a global homogeneous data set that combines the advantages of good spatial coverage of satellite data with good long-term stability of ground-based measurements. One potential use of the derived indices is detection of the expected recovery of the Antarctic ozone hole. The suitability of the derived indicators to this task is discussed in the context of their variability and their susceptibility to saturation effects which makes them less responsive to decreasing stratospheric halogen loading. It is also shown that if the corrections required to match recent Earth Probe TOMS measurements to Dobson measurements are not applied, some of the indictors are affected so as to obscure detection of the recovery of the Antarctic ozone hole.

Declining trend of total ozone column over the northern parts of India

Ozone is one of the important atmospheric trace gases that absorbs both incoming solar near‐ultraviolet and outgoing infrared radiation from the Earth's surface. After the discovery of the ‘ozone hole’, assessment of the long‐term trend of ozone in different regions of the globe has become a frontline topic of research. The present study deals with the variability in the total ozone column over the Indian subcontinent using satellite and limited ground observations. The linear regression technique was applied to the Nimbus and Earth Probe Total Ozone Mapping Spectrometer (EP‐TOMS) data to study the trends during 1997–2003. The rate of decline of ozone is found to be higher in recent years over the northern parts of India, covering the Indo‐Gangetic basin, compared with other parts of India.

Comparison of data for ozone amounts and ultraviolet doses obtained from simultaneous measurements with various standard ultraviolet instruments

Recent technological advances have made measurements of UV doses and ozone column amounts with multichannel filter instruments not only possible, but also an attractive alternative to other more labor-intensive and weather-dependent methods. Filter instruments can operate unattended for long periods of time, and it is possible to obtain accurate ozone column amounts even on cloudy days. We present results from extensive comparisons of the performance of several Norwegian Institute for Air Research UV (NILU-UV) and ground-based (GUV) filter instruments against Dobson and Brewer instruments and the earth probe–total ozone mapping spectrometer (EP-TOMS) instrument. The data used in the comparisons are from four different sites where we have had the opportunity to operate more than one type of UV instrument for extended periods of time. The sites include the University of Oslo, Norway; Ny-Alesund, Spitzbergen, Norway; the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center facilities at Wallops Island, Virginia, and Greenbelt, Maryland; and the University of Alaska, Fairbanks. Our results show that ozone column amounts obtained with current filter-type instruments have an accuracy similar to those obtained with the Dobson instrument. The mean difference between NILU-UV and Dobson direct sun measurements were 0.4±1.9% (1) in Oslo for the period 2000 to 2003. The difference between a GUV and the same Dobson was 1.7±1.4% for the same time period. The mean difference between GUV and TOMS in Ny-Alesund 79 deg N and Oslo 60 deg N in the period 1996 to 1999 was <0.5±3% for days with noon solar zenith angles (SZAs)<80 deg.

Wave activity (planetary, tidal) throughout the middle atmosphere (20-100km) over the CUJO network: Satellite (TOMS) and Medium Frequency (MF) radar observations

Abstract. Planetary and tidal wave activity in the tropopause-lower stratosphere and mesosphere-lower thermosphere (MLT) is studied using combinations of ground-based (GB) and satellite instruments (2000-2002). The relatively new MFR (medium frequency radar) at Platteville (40° N, 105° W) has provided the opportunity to create an operational network of middle-latitude MFRs, stretching from 81° W-142° E, which provides winds and tides 70-100km. CUJO (Canada U.S. Japan Opportunity) comprises systems at London (43° N, 81° W), Platteville (40° N, 105° W), Saskatoon (52° N, 107° W), Wakkanai (45° N, 142° E) and Yamagawa (31° N, 131° E). It offers a significant 7000-km longitudinal sector in the North American-Pacific region, and a useful range of latitudes (12-14°) at two longitudes. Satellite data mainly involve the daily values of the total ozone column measured by the Earth Probe (EP) TOMS (Total Ozone Mapping Spectrometer) and provide a measure of tropopause-lower stratospheric planetary wave activity, as well as ozone variability. Climatologies of ozone and winds/tides involving frequency versus time (wavelet) contour plots for periods from 2-d to 30-d and the interval from mid 2000 to 2002, show that the changes with altitude, longitude and latitude are very significant and distinctive. Geometric-mean wavelets for the region of the 40° N MFRs demonstrate occasions during the autumn, winter and spring months when there are similarities in the spectral features of the lower atmosphere and at mesopause (85km) heights. Both direct planetary wave (PW) propagation into the MLT, nonlinear PW-tide interactions, and disturbances in MLT tides associated with fluctuations in the ozone forcing are considered to be possible coupling processes. The complex horizontal wave numbers of the longer period oscillations are provided in frequency contour plots for the TOMS satellite data to demonstrate the differences between lower atmospheric and MLT wave motions and their directions of propagation.

Dust Storms and Their Impact on Ocean and Human Health: Dust in Earth?s Atmosphere

Satellite imagery has greatly influenced our understanding of dust activity on a global scale. A number of different satellites such as NASA’s Earth-Probe Total Ozone Mapping Spectrometer (TOMS) and Sea-viewing Field-of-view Sensor (SeaWiFS) acquire daily global-scale data used to produce imagery for monitoring dust storm formation and movement. This global-scale imagery has documented the frequent transmission of dust storm-derived soils through Earth’s atmosphere and the magnitude of many of these events. While various research projects have been undertaken to understand this normal planetary process, little has been done to address its impact on ocean and human health. This review will address the ability of dust storms to influence marine microbial population densities and transport of soil-associated toxins and pathogenic microorganisms to marine environments. The implications of dust on ocean and human health in this emerging scientific field will be discussed.

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.

Effect of El Niño on inter-annual variability of ozone during the period 1978-2000 over the Indian subcontinent and China

The paper details the ozone trend over the Indian subcontinent and China inferred from multi-satellite sensors. The present study utilizes data from Nimbus-7, Earth Probe-Total Ozone Mapping Spectrometer (TOMS) and the more recently launched Global Ozone Monitoring Experiment (GOME) sensors. The inter-annual variability of total ozone column (TOC) has been analysed for two periods, from 1979-1993 measured by TOMS and 1996-2000 measured by TOMS and GOME for different Indian cities and Lhasa in Tibet and Beijing in China. The trend was found to be declining over all the major cities with different rates over the period 1979-1993, whereas over the period 1996-2000 the trend was found to increase. The effect of El Niño in 1997-98 on TOC is discussed in light of the prevailing sea surface temperature (SST) anomaly over the Indian Ocean and the Arabian Ocean.

Role of stratospheric air in a severe weather event: Analysis of potential vorticity and total ozone

The role of dry stratospheric air descending to low and middle tropospheric levels in a severe weather outbreak in the midwestern United States is examined using NCEP Eta model output, Rapid Update Cycle (RUC) analyses, and Earth probe Total Ozone Mapping Spectrometer (EP/TOMS) total ozone data. While stratospheric air was not found to play a direct role in the convection, backward trajectories show stratospheric air descended to 800 hPa just west of the convection. Damaging surface winds not associated with thunderstorms also occurred in the region of greatest stratospheric descent. Small‐scale features in the high‐resolution total ozone data compare favorably with geopotential heights and potential vorticity fields, supporting the notion that stratospheric air descended to near the surface. A detailed vertical structure in the potential vorticity appears to be captured by small‐scale total ozone variations. The capability of the total ozone to identify mesoscale features assists model verification. The total ozone data suggest biases in the RUC analysis and Eta forecast of this event. The total ozone is also useful in determining whether potential vorticity is of stratospheric origin or is diabatically generated in the troposphere.

Ozone column density determination from direct irradiance measurements in the ultraviolet performed by a four-channel precision filter radiometer

Ultraviolet light was measured at four channels (305, 311, 318, and 332 nm) with a precision filter radiometer (UV-PFR) at Arosa, Switzerland (46.78 degrees , 9.68 degrees , 1850 m above sea level), within the instrument trial phase of a cooperative venture of the Swiss Meteorological Institute (MeteoSwiss) and the Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center. We retrieved ozone-column density data from these direct relative irradiance measurements by adapting the Dobson standard method for all possible single-difference wavelength pairs and one double-difference pair (305/311 and 305/318) under conditions of cloud-free sky and of thin clouds (cloud optical depth <2.5 at 500 nm). All UV-PFR retrievals exhibited excellent agreement with those of collocated Dobson and Brewer spectrophotometers for data obtained during two months in 1999. Combining the results of the error analysis and the findings of the validation, we propose to retrieve ozone-column density by using the 305/311 single difference pair and the double-difference pair. Furthermore, combining both retrievals by building the ratio of ozone-column density yields information that is relevant to data quality control. Estimates of the 305/311 pair agree with measurements by the Dobson and Brewer instruments within 1% for both the mean and the standard deviation of the differences. For the double pair these values are in a range up to 1.6%. However, this pair is less sensitive to model errors. The retrieval performance is also consistent with satellite-based data from the Earth Probe Total Ozone Mapping Spectrometer (EP-TOMS) and the Global Ozone Monitoring Experiment instrument (GOME).

Tropical tropospheric ozone and biomass burning.

New methods for retrieving tropospheric ozone column depth and absorbing aerosol (smoke and dust) from the Earth Probe-Total Ozone Mapping Spectrometer (EP/TOMS) are used to follow pollution and to determine interannual variability and trends. During intense fires over Indonesia (August to November 1997), ozone plumes, decoupled from the smoke below, extended as far as India. This ozone overlay a regional ozone increase triggered by atmospheric responses to the El Niño and Indian Ocean Dipole. Tropospheric ozone and smoke aerosol measurements from the Nimbus 7 TOMS instrument show El Niño signals but no tropospheric ozone trend in the 1980s. Offsets between smoke and ozone seasonal maxima point to multiple factors determining tropical tropospheric ozone variability.