Total Ozone Mapping Spectrometer Satellite Research Articles

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.

Global and Hemispherical Interannual Variation of Total Column Ozone from TOMS and OMI Data

Daily Total Column Ozone (TCO) measurements compiled from Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instruments (OMI) were used to analyze the global and hemispherical TCO interannual variations. Two periods of TCO measurements were analyzed separately covering full years. For the 1978-1994 period, the TCO showed a global decade decrease rate of 13.45 DU (about -4.3%). For the Northern Hemisphere(NH) the decade decrease rate was of 12.96 DU (-4.0%), while in the Southern Hemisphere (SH) was of 13.57 DU (-4.5%). These decreases in ozone trends, using the totality of TOMS and OMI satellite measurements, are greater than those reported in literature. The 1998-2014 period global TCO decade decrease rate was of 1.56 DU, corresponding 0.94 DU and 0.138 DU for the NH and SH, respectively. The global TCO variations must show a double annual periodicity, the first one with maxima in March due to the Northern Hemisphere (NH) and the second one during September due to the Southern Hemisphere (SH). However, the maxima due to SH TCO interannual variations have gradually vanished. A disturbance in the SH TCO interannual variations has appeared since 1980; graphically the periodicity brakes down and transforms to a double peak from 1985 and on. This effect can be attributed to the hemispheric impact of the ozone hole at the South Pole. Between October 1, 2004 and December 14, 2005 TOMS and OMI have recorded this disturbance unequivocally. We conclude that the disturbance in SH TCO has an irreversible character.

Synoptic study of the seasonal variability of dust cases observed by the TOMS satellite over northern Saudi Arabia

The aerosol index (AI) from the Total Ozone Mapping Spectrometer (TOMS) satellite and meteorological parameters from National Center for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets were used to examine seasonal dust cases in northern Saudi Arabia. Considering all seasons, winter has the fewest dust cases, whereas summer has the most dust cases. Synoptically, surface high-pressure systems in the eastern and western regions are important for the occurrence of dust cases over the northern Arabian Peninsula. When the eastern high pressure prevails, the effects of the Indian low-pressure system on the Arabian Peninsula are weakened or become nonexistent. The extension of the western high-pressure system toward the southeast provides an opportunity for a low-pressure system over Southeast Africa to connect with the Indian low-pressure system, which increases the width of the low-pressure trough and affects the Arabian Peninsula by increasing the amount of dust over the region. At 850 hPa, the weather systems typically rotate clockwise between winter and autumn. In winter, cyclonic systems prevail in the northern region, while anticyclonic systems prevail in the south. The systems are oriented toward the northeast in spring, the west in summer, and the southeast in autumn. Moreover, northern cyclones at 500 hPa shrink as they move northward and the maximum wind speed at 250 hPa decreases from winter to summer. Furthermore, the case study confirms that a change in the relative strength of the pressure systems and a change in the orientation of the isobars (contours) affect the amount of dust over the area. When the orientation of the isobar (contour) lines become strictly north to south or east to west, the amount of dust decreases and vice versa.

Synoptic features associated with dust transition processes from North Africa to Asia

Aerosol index data from the total ozone mapping spectrometer satellite and reanalysis data from the National Center for Environmental Prediction and the National Center for Atmospheric Research are useful in the study of synoptic properties of the dust storms that carry dust from North Africa to Asia during the spring season for the period 1979 to 2006. In this study, we analyzed the synoptic properties of dust cases that pass through the transition zone between North Africa and Asia. We identified the dust cases to study by looking, inside transition zone, at events with an aerosol index greater than 2. We then divided the identified cases, depending on the spread and strength of the dust inside the transition zone, into seven categories ranging from weak events to moderate events to violent events. We found the common synoptic characteristics in all these categories as follows: The high pressure belt located over northern Africa allows the low pressure belt located over the South African Sahara to move northward; a pressure gradient between these two atmospheric systems directs from south to north; an increase in the pressure gradient leads to increased in both of the event’s dust and the amount of dust moves to North Africa from the Sahara; an additional pressure gradient between the western Azores high pressure system and the low pressure system located over the Arabian Peninsula directs from west to east; the stronger the pressure gradient, the greater the amount of dust in the event and moving a large amount of dust from Northeast Africa to Asia. To verify that these characteristics capture the essence of dust events from North Africa to Asia, we checked if they were also common to two additional extremes categories and two extremes events. The results confirmed the continued existence of these common characteristics.

Temporal and spatial variability of total ozone column using TOMS satellite observations and comparison with measurements from the Dobson network

This article presents a detailed analysis of seasonal and interannual variability of total ozone content (TOC) at 16 different stations in Africa using Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) data for a period of 14 years (January 1979–December 1992). The analysis provides not only an estimate of the long-term annual and seasonal trends but also statistics of means and variability of ozone on temporal and spatial scales. For example, high negative deviations were observed for stations in Northern Africa in spring (March–May), with as much as –20 DU in Alexandria. A comparison of total ozone column data retrieved from the TOMS satellite with measurements obtained from the Dobson ground-based network is further presented for Cairo, Irene, Nairobi and Springbok. Estimates of the percentage seasonal difference between TOMS satellite and Dobson ground-based measurements reveal that the ground measurements were higher in magnitude at all stations with the exception of Nairobi. To verify the level of correlation between the ground-based and satellite observations, rank correlation coefficients were determined for all stations using daily and monthly observations. The results show that there is good correlation between the compared data sets, with daily coefficient of determination (r 2) values of 0.87, 0.76, 0.58 and 0.87 for Cairo, Irene, Nairobi and Springbok, respectively.

Monitoring spatio-temporal aerosol patterns over Pakistan based on MODIS, TOMS and MISR satellite data and a HYSPLIT model

Three different satellite-borne sensors, namely the Total Ozone Mapping Spectrometer (TOMS), the Moderate Resolution Imaging Spectroradiometer (MODIS), and the Multi-angle Imaging Spectroradiometer (MISR), were used to investigate the spatial and temporal variations of aerosols over several cities in Pakistan. A Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used for trajectory analysis in order to reconstruct the origins of air masses and understand the spatio-temporal variability of aerosol concentrations. Recent MODIS aerosol data (2002–2008) and earlier TOMS data (1979–2001) revealed increasing concentrations of aerosols over Pakistan and adjacent areas. Validation of MODIS and MISR derived aerosol optical depths (AODs) with Aerosol Robotic Network (AERONET) data for 2007 demonstrated that the MISR data was more accurate when close to the ocean, while the MODIS was more accurate over vegetated areas. The relationship between MODIS and MISR AOD data from 2002 to 2008 was analyzed, revealing a strong correlation between the two datasets. An assessment of seasonal variability in AOD for industrial, urban, semi-urban, rural, and semi-arid areas revealed maximum AOD values during the summer over all the areas investigated. Back trajectory analyses indicated that while winter air masses reaching Pakistan had travelled long distances, summer air masses had travelled only short distances. The higher aerosol concentrations during the summer are interpreted to be a result of the air masses spending more time over land during the summer than they do during the winter. While monsoonal rainfall tends to reduce aerosol concentrations by washing aerosols out of the atmosphere, this effect is mainly restricted to the eastern and south-eastern parts of Pakistan. ► This study carried out the spatial and temporal variations of aerosols over several cities in Pakistan. ► TOMS (1979–2001) and MODIS aerosol data (2002–2008) revealed increasing concentrations of aerosols over Pakistan. ► The spatial correlation between MODIS and MISR AOD found to be higher in winter than in summer. ► The MISR provides better AOD estimates close to the ocean while MODIS provides better over terrestrial regions. ► The highest mean AODs were recorded during the summer and the lowest AODs in the winter.

Spatial Distribution and Temporal Variation of Solar UV Radiation over the Tibetan Plateau

The Tibetan Plateau has very high levels of ultraviolet radiation. To study the UV radiation across the Tibetan Plateau, data from the TOMS (Total Ozone Mapping Spectrometer) satellite for the periods 1979 -1992 and 1997–¬ 2003 are used. The analysis shows a 21-year average of the spatial distribution of daily summer erythemal UV doses across the Tibetan Plateau and its vicinity with a spatial resolution of 1° Lat. - 1.25° Long., also obtains temporal variations during the period 1979 ¬- 2003 of UV radiation for the region by selecting seven locations across the Tibetan Plateau and its neighboring areas. The results show that during the summer months from May to August the average daily erythemal UV doses at the selected seven sites across the Tibetan Plateau range from 7.5 to 9.0 kJ/m2. These daily erythemal UV doses are considerably higher than those observed at geographically close, lower-altitude locations such as Chengdu in China and New Delhi in India, which had corresponding values of 4.1 kJ/m2 and 5.8 kJ/m2, respectively. During the period from 1979 to 1992 observe a clear trend of increasing erythemal UV doses over the Tibetan Plateau. Comparisons between satellite derived UV radiation and ground-based measurements of UV radiation for Lhasa are made.

The Northern Path of Asian Dust Transport from the Gobi Desert to North America

AbstractThe aerosol index (AI) of the Total Ozone Mapping Spectrometer (TOMS) satellite data (1979-2001) was analyzed to reveal the climatological long-distance path of dust transport from Asia to North America. The AI in the west coast of the United States is highly correlated with that in the Gobi desert. Additionally, from the TOMS satellite images, it can be seen that very strong plumes advect from Asia to the west coast of North America in typical dust storm cases. When applying the source-receptor relationship to detect the northern dust transport path between the Gobi source region and the west coast of the United States receptor region, it is evident that the dust plume can be transported northward beyond 60°N from its source region and that it takes 5 to 6 days to reach the west coast of the United States. The cross correlation technique shown in this work is a useful tool that can be applied in other regions to give useful insights into relationships between major dust sources and downwind recep...

Natural versus anthropogenic aerosols in the eastern Mediterranean basin derived from multiyear TOMS and MODIS satellite data

In the present study we investigate the spatial and temporal variation of aerosol optical thickness (AOT) in the eastern Mediterranean basin, and more specifically in the area extending from 28.5°N to 42.5°N and from 18.5°E to 35.5°E, which includes large urban areas and megacities such as Cairo, Istanbul, Athens, Izmir, Ankara, and Thessaloniki. For this purpose we use long‐term AOT data from the Total Ozone Mapping Spectrometer (TOMS) version2 converted to 500 nm (AOT500) for the period 1980–2001 and Collection 005 AOT data at λ = 550 nm (AOT550) from Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites for the periods 2000–2005 and 2002–2005, respectively. The spatial and temporal variation of AOT shows a good agreement between TOMS and MODIS, in terms of geographical patterns, which maximizes the usefulness of TOMS AOT product given its long temporal coverage (climatological). According to MODIS‐Terra, the annual mean AOT550 over the studied region equals 0.22 ± 0.05 (monthly values ranging from 0.14 to 0.32) and shows strong spatial inhomogeneities. The smallest values (down to 0.1) occur over the western, and especially in the northwestern, part of Greece, over the northern part of Anatolian peninsula and also over the sea of east Mediterranean. The largest AOT values (up to about 1.0) occur over northern Africa, Middle East, and the adjacent coasts, and over the Anatolian plateau. These high aerosol loadings are of natural origin, mainly desert dust. However, very large values (up to 0.8) are also found over large urban areas surrounding megacities, associated with anthropogenic, apart from natural desert, aerosols. By using TOMS AOT data as proxy for the dust source, and the difference of MODIS‐TOMS AOT as an indicator of the anthropogenic aerosol component, the relative contribution of natural versus anthropogenic sources of aerosols has been derived for the eastern Mediterranean area. Limitations of this approach are discussed and the associated uncertainties are also evaluated and discussed.

Quasi‐biennial oscillation and tracer distributions in a coupled chemistry‐climate model

We have used a fully coupled chemistry‐climate model (CCM), which generates its own wind and temperature quasi‐biennial oscillation (QBO), to study the effect of coupling on the QBO and to examine the QBO signals in stratospheric trace gases, particularly ozone. Radiative coupling of the interactive chemistry to the underlying general circulation model tends to prolong the QBO period and to increase the QBO amplitude in the equatorial zonal wind in the lower and middle stratosphere. The model ozone QBO agrees well with Stratospheric Aerosol and Gas Experiment II and Total Ozone Mapping Spectrometer satellite observations in terms of vertical and latitudinal structure. The model captures the ozone QBO phase change near 28 km over the equator and the column phase change near ±15° latitude. Diagnosis of the model chemical terms shows that variations in NOx are the main chemical driver of the O3 QBO around 35 km, i.e., above the O3 phase change.

A satellite chronology of the May–June 2003 eruption of Anatahan volcano

The first recorded eruption of Anatahan began at approximately 17:00 local time on May 10, 2003. Here, we present observations made by a suite of Earth-orbiting satellites of the heat, ash and gas emitted from the volcano before, during and after the eruption. No thermal or sulphur dioxide emissions are apparent in MODIS (Moderate Resolution Imaging Spectroradiometer), AIRS (Atmospheric Infrared Sounder), EP TOMS (Earth Probe Total Ozone Mapping Spectrometer) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite images acquired prior to the eruption. However, within 24 h of eruption onset, the University of Hawaii's near-real-time satellite thermal monitoring system ‘MODVOLC’ detected the eruption and confirmed Anatahan's eastern caldera as the center of the activity. Although the eruption was initially phreatic, it quickly transitioned into a magmatic phase that culminated in the emplacement of a dacitic lava dome. The onset of the magmatic phase is recorded by MODVOLC as an order of magnitude increase in the heat flux from the volcano after May 16, indicative of fresh lava at the surface, relative to low values (50–90 MW) observed during the initial phreatic phase. MODVOLC detected thermal emission from the volcano on a further 22 occasions during the next 2 weeks, allowing us to quantitatively document temporal variations in thermal output during the eruption. We use MODIS, EP TOMS and AIRS data to document ash and sulphur dioxide emissions from Anatahan covering the period May 10–June 13, 2003. Using daily satellite observations in conjunction with ground-based estimates, we arrive at a total SO 2 discharge of ∼ 0.51 Mt for the ∼ 1 month of activity, of which ∼ 0.11 Mt was emitted during activity on May 10–12. Decreases in measured SO 2 flux prior to the observation of a lava dome on June 4 indicate that the emerging dome may have blocked the upper conduit and inhibited degassing during this period. A new episode of dome growth was detected by MODVOLC on April 12, 2004. So far, the level of thermal emission during the recent period of activity is substantially lower than that observed during the May–June 2003 eruption.

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.

TOMS‐derived erythemal irradiance versus measurements at the stations of the Argentine UV Monitoring Network

The major factors causing differences between satellite‐derived and ground‐based ultraviolet (UV) erythemal irradiances and doses are discussed. Measurements totaling more than 4700 days during 1997–1999 were obtained at 8 stations (22°S–64°S) of the Argentine UV Monitoring Network. The satellite retrieval uses radiative transfer calculations for cloud‐ and aerosol‐free conditions multiplied by correction factors for clouds and aerosols. Key parameters are total ozone, cloud optical depth, and surface albedo derived from Total Ozone Mapping Spectrometer (TOMS). When no aerosol correction is applied, systematic differences of satellite‐derived erythemal irradiance relative to ground‐based measurements amount to +1% at a tropical high‐altitude Andean location, +10% at stations in the central Pampas, +5% at southern Patagonian sites, and −7% at the southernmost continental and Antarctic stations with varying snow cover. When an aerosol correction is applied by estimating “minimum” and “maximum” aerosol loading, the systematic differences are within ±10% for all “snow‐free” stations. To reduce the differences at places with varying snow conditions, an “average surface‐albedo climatology” must be used instead the TOMS climatology of minimum albedo. Although the statistical uncertainty of the differences increases with TOMS reflectivity, the systematic difference is independent of TOMS reflectivity for most of the stations, so on average the comparison for cloudy situations is as good as for clear‐sky conditions. The comparison for daily erythemal doses gives similar results with smaller statistical uncertainty. Measured uncertainties are in agreement with a theoretical analysis. For most locations, well‐characterized ground‐based instruments should agree with TOMS satellite estimations within 10% if aerosol corrections are known.

Re‐evaluation of SO2 release of the 15 June 1991 Pinatubo eruption using ultraviolet and infrared satellite sensors

In this study, ultraviolet TOMS (Total Ozone Mapping Spectrometer) satellite data for SO2 are re‐evaluated for the first 15 days following the 15 June 1991 Pinatubo eruption to reflect new data retrieval and reduction methods. Infrared satellite SO2 data from the TOVS/HIRS/2 (TIROS (Television Infrared Observation Satellite) Optical Vertical Sounder/High Resolution Infrared Radiation Sounder/2) sensor, whose data sets have a higher temporal resolution, are also analyzed for the first time for Pinatubo. Extrapolation of SO2 masses calculated from TOMS and TOVS satellite measurements 19–118 hours after the eruption suggest initial SO2 releases of 15 ± 3 Mt for TOMS and 19 ± 4 Mt for TOVS, including SO2 sequestered by ice in the early Pinatubo cloud. TOVS estimates are higher in part because of the effects of early formed sulfate. The TOMS SO2 method is not sensitive to sulfate, but can be corrected for the existence of this additional emitted sulfur. The mass of early formed sulfate in the Pinatubo cloud can be estimated with infrared remote sensing at about 4 Mt, equivalent to 3 Mt SO2. Thus the total S release by Pinatubo, calculated as SO2, is 18 ± 4 Mt based on TOMS and 19 ± 4 Mt based on TOVS. The SO2 removal from the volcanic cloud during 19–374 hours of atmospheric residence describes overall e‐folding times of 25 ± 5 days for TOMS and 23 ± 5 days for TOVS. These removal rates are faster in the first 118 hours after eruption when ice and ash catalyze the reaction, and then slow after heavy ash and ice fallout. SO2 mass increases in the volcanic cloud are observed by both TOMS and TOVS during the first 70 hours after eruption, most probably caused by the gas‐phase SO2 release from sublimating stratospheric ice‐ash‐gas mixtures. This result suggests that ice‐sequestered SO2 exists in all tropical volcanic clouds, and at least partially explains SO2 mass increases observed in other volcanic clouds in the first day or two after eruption.

Long‐term trends in tropospheric ozone over the Indian tropical region

We report a statistical regression model analysis of long‐term linear trends in the ozonesonde vertical profiles in the troposphere for the period 1972–2001 from the three tropical stations in tropical India. An analysis of tropospheric column ozone (TCO) data derived from ozonesonde and Nimbus7/Earth Probe ‐total ozone mapping spectrometer (TOMS) during the period 1979–2002 has also been done. There are no statistically significant trends over Trivandrum (8.3°N, 76.6°E, 61 m) but significant positive trend (within 2‐sigma error) are found to occur in the lower troposphere over Pune (18.3°N, 73.5°E, 559 m) and throughout the entire troposphere over a heavily air‐polluted urban center Delhi (28.4°N, 77.1°E, 216 m). However, over the last decade, variations in tropospheric ozone have become statistically insignificant even over Delhi in spite of increasing surface NOx concentrations. The TCO obtained by ozonesonde as well as TOMS satellite data over Trivandrum do not reveal any statistically significant trend.

Ozone signatures of climate patterns over the Euro‐Atlantic sector in the spring

AbstractThe influence of low‐frequency tropospheric dynamics upon column ozone interannual variability is estimated in the spring season over the Euro‐Atlantic sector. This dynamical variability of tropospheric origin is examined in terms of leading climate patterns, derived from an empirical orthogonal function analysis of the National Center for Environmental Prediction 500 mb geopotential height analyses. In order to fingerprint the spatial and temporal ozone signatures of these patterns, the Total Ozone Mapping Spectrometer satellite observations of column ozone during the last two decades are used. The geographical ozone signatures of these climate patterns are extracted by linear regression and their time evolution reconstructed.Geopotential anomalies associated with four leading patterns of variability (the North Atlantic Oscillation (NAO), the Scandinavian pattern, the east Atlantic pattern and the European blocking pattern) induce column ozone anomalies in the range of 5–15 Dobson Units per standard deviation of the pattern index. The impact of these combined Euro‐Atlantic climate patterns upon the regional ozone trends and interannual variability is also estimated. In order to reconstruct the regional ozone trend and variability, it proved important to incorporate several patterns, in addition to the dominant NAO. A hitherto little‐known lifting of the Arctic tropopause by the polar night jet is also shown to imprint upon the ozone signatures of some patterns. Copyright © 2003 Royal Meteorological Society

Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology 1. Comparison with Total Ozone Mapping Spectrometer (TOMS) and ground‐based measurements

A network of 10 southern hemisphere tropical and subtropical stations, designated the Southern Hemisphere Additional Ozonesondes (SHADOZ) project and established from operational sites, provided over 1000 ozone profiles during the period 1998–2000. Balloon‐borne electrochemical concentration cell (ECC) ozonesondes, combined with standard radiosondes for pressure, temperature, and relative humidity measurements, collected profiles in the troposphere and lower to midstratosphere at: Ascension Island; Nairobi, Kenya; Irene, South Africa; Réunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristóbal, Galapagos; and Natal, Brazil. The archived data are available at: 〈http://croc.gsfc.nasa.gov/shadoz〉.1 In this paper, uncertainties and accuracies within the SHADOZ ozone data set are evaluated by analyzing: (1) imprecisions in profiles and in methods of extrapolating ozone above balloon burst; (2) comparisons of column‐integrated total ozone from sondes with total ozone from the Earth‐Probe/Total Ozone Mapping Spectrometer (TOMS) satellite and ground‐based instruments; and (3) possible biases from station to station due to variations in ozonesonde characteristics. The key results are the following: (1) Ozonesonde precision is 5%. (2) Integrated total ozone column amounts from the sondes are usually to within 5% of independent measurements from ground‐based instruments at five SHADOZ sites and overpass measurements from the TOMS satellite (version 7 data). (3) Systematic variations in TOMS‐sonde offsets and in ground‐based‐sonde offsets from station to station reflect biases in sonde technique as well as in satellite retrieval. Discrepancies are present in both stratospheric and tropospheric ozone. (4) There is evidence for a zonal wave‐one pattern in total and tropospheric ozone, but not in stratospheric ozone.

Comparison of Brewer ultraviolet irradiance measurements with total ozone mapping spectrometer satellite retrievals

Comparison of measured UV irradiance with estimates from satellite observation is potentially effective for the validation of data from the two sources. Summer data from ten Canadian Brewer sites were compared in this study with noon UV irradiance estimated from total ozone mapping spectrometer (TOMS) measurements. In general, TOMS estimates can successfully reproduce long-term and major short-term UV variations. However, there are some systematic differences between the measurements at the ground and satellite-retrieved UV irradiance. From 3 to 11% of the Brewer-TOMS difference can be attributed to the Brewer angular response error. This error depends on the solar zenith angle and cloud conditions, and is different from instrument to instru- ment. When the angular response of the Brewer instrument is consid- ered and applied, the Brewer data are still lower than TOMS-estimated UV irradiance by 9 to 10% on average at all sites except one. The dif- ference is close to zero at one station (Saturna Island), possibly due to its much cleaner air. The bias can be seen in clear sky conditions and at the 324-nm wavelength, i.e., it is not related to local cloud conditions or absorption by ozone or SO2 . © 2002 Society of Photo-Optical Instrumentation

Impact of vegetation and preferential source areas on global dust aerosol: Results from a model study

We present a model of the dust cycle that successfully predicts dust emissions as determined by land surface properties, monthly vegetation and snow cover, and 6‐hourly surface wind speeds for the years 1982–1993. The model takes account of the role of dry lake beds as preferential source areas for dust emission. The occurrence of these preferential sources is determined by a water routing and storage model. The dust source scheme also explicitly takes into account the role of vegetation type as well as monthly vegetation cover. Dust transport is computed using assimilated winds for the years 1987–1990. Deposition of dust occurs through dry and wet deposition, where subcloud scavenging is calculated using assimilated precipitation fields. Comparison of simulated patterns of atmospheric dust loading with the Total Ozone Mapping Spectrometer satellite absorbing aerosol index shows that the model produces realistic results from daily to interannual timescales. The magnitude of dust deposition agrees well with sediment flux data from marine sites. Emission of submicron dust from preferential source areas are required for the computation of a realistic dust optical thickness. Sensitivity studies show that Asian dust source strengths are particularly sensitive to the seasonality of vegetation cover.

Evaluating Ultraviolet Radiation Exposure with Satellite Data at Sites of Amphibian Declines in Central and South America

Abstract: Many amphibian species have experienced substantial population declines or have disappeared altogether during the last several decades at a number of amphibian survey sites in Central and South America. Our study addresses the use of trends in solar UV‐B radiation exposure (280–320 nm) at these sites over the last two decades, derived from the Total Ozone Mapping Spectrometer satellite data. It is intended to demonstrate a role for satellite observations in determining whether UV‐B radiation is a contributing factor in amphibian declines. We used these data to calculate the daily erythemal (sunburning) UV‐B, or UV‐Bery , exposure at the latitude, longitude, and elevation of each of 20 survey sites. The annually averaged UV‐Bery dose, as well as the maximum values, have been increasing in both Central and South America, with higher levels reached at the Central American sites. The annually averaged UV‐Bery exposure increased significantly from 1979–1998 at all 11 Central American sites we examined (r 2 = 0.60–0.79; p≤ 0.015), with smaller but significant increases at five of the nine South American sites (r 2 = 0.24–0.42; p≤ 0.05). The number of days having the highest UV‐B exposure (≥6.75 kJ/m2/day) increased in both regions from <40 days per year to approximately 58 days per year in 1998 (r2 = 0.24–0.42; p≤ 0.001). In Central America, the contribution of these very high UV‐Bery exposure levels to the annual UV‐Bery total increased from approximately 5 to approximately 15% over the 19‐year period, but actual daily exposures for each species are unknown. A UV‐B ratio, the highest monthly UV‐B exposure relative to the annual average for the highest UV‐B category (≥6.75 kJ/m2), increased in both regions over this time period (r 2 = 0.73; p≤ 0.001). This UV index was consistently higher for Central America, where species declines have been the most severe. These results should justify further research into whether UV‐Bery radiation plays a role in amphibian population declines and extinctions. We discuss synergy among UV‐B radiation and other factors, especially those associated with alterations of water chemistry (e.g., acidification) in aqueous habitats.