Comparison of vertical ozone profiles as deduced from remote and in situ sensing techniques

A number of vertical ozone profiles up to 35 km in height, have been measured using balloon-based sensors at Athens, Greece (38^° N, 24^° E). The measurements were made during the winter of 1991-1992, as part of the European Arctic Stratospheric Ozone Experiment (EASOE). The data collected during the balloon ascents have been compared with those during the balloon descents. Both profiles are compared with the total ozone measurements derived from the TOMS on the Nimbus-7 satellite and the Dobson spectrophotometer.     

Total ozone observations at Athens,Greece by satellite-borne and ground-based instrumentation

A comparison is made of total ozone (TOZ) content observations conducted by the Dobson spectrophotometer No. 118, the SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY), the Total Ozone Mapping Spectrometer (TOMS) and the Ozone Monitoring Instrument (OMI) over Athens, Greece, during 1991–2008. Spearman's and Wilcoxon's tests were used to determine the measure of the agreement between the ground-based and satellite column ozone data. The correlation coefficient between Dobson and Nimbus-7, ADEOS, Earth Probe, OMI and SCIAMACHY observations was found to be 0.95, 0.96, 0.94, 0.93 and 0.87, respectively, while the correlation coefficient between total ozone observations of SCIAMACHY and Earth Probe-TOMS and OMI is 0.85 and 0.93, respectively. SCIAMACHY overestimates the column ozone with respect to Dobson, Earth Probe-TOMS and OMI by 10, 15 and 3 DU, respectively, while Dobson underestimates the column ozone with respect to Nimbus-7, ADEOS and OMI by 5, 10 and 8 DU. The results obtained confirm that the Athens Dobson station may continue to be considered as a ground-truth total ozone station for the validation of the satellite column ozone observations. In addition, linear regression analysis of the deseasonalized monthly mean column ozone, as derived from Dobson measurements, gives an increase of +0.33 ± 0.07% per year during 1991–2000 and a decrease of –0.33 ± 0.07% per year for the period 2001–2008.     

On the accuracy of total ozone measurements made with a Dobson spectrophotometer in Athens

Since 1989, total ozone measurements with the Dobson spectrophotometer No. 118 have been made in Athens (38°N, 24°E), which has been suffering from severe air pollution problems during the last fifteen years. These measurements are subject to errors caused by interfering gases that absorb solar ultraviolet radiation in the region of the Dobson instrument's wavelengths (300-400 nm). In the urban area of Athens, the measured S0₂ and N0₂ mixing ratios have been found to lead to total ozone errors of up to 2-5 per cent during the year 1991. To examine the consistency of Dobson measurements, the integrated ozone profiles from a number of ozonesoundings performed at Athens have been used also.     

Three years of total ozone measurements over Athens obtained using the remote sensing technique of a Dobson spectrophotometer

Total ozone measurements with a Dobson spectrophotometer (No. 118) have been instituted in Athens (37.9° N, 23.8° E) from 1989 and they now form part of the data published by the World Meteorological Organization, World Ozone Data Center. We have used this data set in order to examine the consistency of data from the Total Ozone Mapping Spectrometer (flown on the Nimbus-7 satellite) with the corresponding Dobson data on a daily basis.

The results show that the Athens station may be used to provide ground truth for satellite-based total ozone measurements and also for providing reasonably accurate total ozone values for south eastern Europe.     

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.     

Technical Report: Standardization of the Athens Dobson spectrophotometer versus Reference Dobson spectrophotometer 064

The comparison between Dobson spectrophotometer number 118 operating in Athens, Greece, and the Reference Instrument Dobson number 064 (Hohenpeissenberg, Germany) for column ozone observations, is discussed. The results obtained showed that the highest difference in total ozone observations derived from those instruments is almost 0.6% when the μ value ranges from 1.2 to 2.5, and hence no data reprocessing of historical data from Athens is necessary.     

On the total ozone depletion over Greece derived from satellite-flown and ground-based instruments

There is abundant evidence of the depletion of atmospheric ozone concentration, both from ground-based measurements and from satellite data. However, one set of data published in 1989 by Bais et al. relating to Thessaloniki, in northern Greece, reported no depletion but rather said ‘the period March 1982 to March 1988 shows an insignificant change of total ozone, of about +0-02 per cent per year’. The data of Thessaloniki, obtained from the same instrument (Brewer spectrophotometer no. 5) as that used by Bais et al. has now also been published in the Red Book. In this paper we examine TOMS data for Thessaloniki, Athens and Crete for the six-year period from March 1982 to March 1988 and find a common ozone depletion of the order of 30 per cent during this period, for each of these three sites, including Thessaloniki; this is in contradiction to the results of Bais et al. for Thessaloniki. We have analysed the Red Book data for Thessaloniki and found that it shows total ozone depletion consistent with the results obtained from TOMS data, which are themselves consistent with results from other ground-based measurements in mid-latitudes. It is concluded that there are errors both in the data presented by Bais et al. and in their analysis and, in particular, that their statement quoted above is incorrect and should be disregarded.     

Comparison of total ozone measurements from a differential optical absorption filter instrument and a Dobson spectrophotometer

Measures of total ozone at Lisbon in July 1996 taken with a differential optical absorption filter instrument (UAM-DOAF) and a Dobson spectrophotometer are compared. Correlation of the UAM-DOAF measures and NOAATOVS data from April to October 1996 and NASA Earth Probe TOMS data from July to October 1996 for Madrid (40 N, 3 W) are given. Results show that the UAM-DOAF instrument can be used with approximately a 3 per cent error in estimating short-term total ozone variations.     

Cover Application of the NOAA-AVHRR images to the study of the large forest fires in Spain in the summer of 1994.

Ozone vertical profiles derived from Umkehr observations by the Dobson spectrophotometer at Belsk (52.50° N, 20.47° E) and from ozone soundings carried out at the nearest aerological station, Legionowo (52.24° N, 20.58° E), have been compared with those measured by the MLS instrument on board the Aura spacecraft during the sites' overpasses for the period 2004–2005. It is assumed that the satellite station distance should be less than 2° and less than 4° for the latitudinal and longitudinal difference, respectively. The bias, RMS error, and the correlation coefficients between the ozone content in the Umkehr layers have been calculated using Dobson/sonde/MLS data. The ozone mixing ratio at selected levels in the lower and mid‐stratosphere (from 215 hPa up to 6.8 hPa) have been compared using the sonde/MLS data. The number of analysed daily values was ～40 (Dobson/MLS), 60 (sonde/MLS), and 60 (Dobson/sonde) since August 2004. The comparisons show a good correspondence (bias ～±5%, RMS <10%, correlation coefficient >0.5) between the ozone content in Umkehr layers 4–8 and ozone mixing ratio at pressures <50 hPa. At lower stratosphere (Umkehr layer 3) and upper stratosphere (Umkehr layer 9), there is also statistically significant relationship between the data, but the biases and RMS are ～2 times larger, while the correlation coefficients are still high (>0.7).     

On the variation of the tropospheric ozone over Indian region in relation to the meteorological parameters

Using monthly mean satellite measurements of TOMS/SBUV tropospheric ozone residual (TOR) data and meteorological parameters (tropopause height (TPH), 200 hPa geopotential height (GPH) and outgoing longwave radiation (OLR)) during 1979–2001, seasonal variability of TOR data and their association with meteorological parameters are outlined over the Indian region. Prominent higher values of TOR (44–48 DU, which is higher than the globally averaged 31.5 DU) are observed over the northern parts of the country during the summer monsoon season (June–September). Similar to the TOR variation, meteorological parameters (tropopause height, 200 hPa geopotential height and outgoing longwave radiation) also show higher values during the summer monsoon season, suggesting an in phase relationship and strong association between them because of deep convection present during summer monsoon time. The monthly trends in TOR values are found to be positive over the region. TOR has significant positive correlations (5% level) with GPH, and negative correlations with OLR and TPH for the month of September. The oxidation chains initiated by CH₄ and CO show the enhanced photochemical production of ozone that would certainly become hazardous to the ecological system. Interestingly, greenhouse gases (GHG) emissions were found to have continuously increased over the Indian region during the period 1990–2000, indicating more anthropogenic production of ozone precursor gases causing higher level of tropospheric ozone during this period.     

On the statistical analysis of the ozone depletion over Greece

This study reports trends derived from the TOMS reprocessed total ozone data, as well as from total ozone measurements taken at the University of Athens with a Dobson Spectrometer. The period from January 1979 to May 1994 is examined. The data analysed exhibit a significant negative trend of total ozone from the mid-eighties until the end of the period.     

On the longitude dependence of total ozone trends over middle-latitudes

It has recently been observed that the total ozone trends derived from certain geographical regions such as the Mediterranean and Athens (Greece) show similar values to those derived from the 40°N zonal averaged column ozone data. In this Letter, the total ozone concentration, collected by the Total Ozone Mapping Spectrometer (TOMS) flown on Nimbus-7 and Meteor-3 during the time-period January 1979-December 1993, as well as by Earth Probe during the time-period January 1997-May 2001, for the Mediterranean, Athens (Greece) and Srinagar (India), is analysed. Further, the harmonic analysis performed on total ozone time-series provides a proper tool to interpret the observed similarity in total ozone seasonal trends, which may probably be attributed to the effect of planetary waves on the ozone distribution.     

Total ozone over Ankara and its forecasting using regression models

The present study is concerned with the total ozone variation in Ankara, Turkey (39°57′ N; 32°53′ E) and developing a total ozone prediction model by Total Ozone Mapping Spectrometer (TOMS) and single-site aerological data (1984–2006). The daily averages of the total column ozone over Ankara show a seasonal variation, with larger values in spring/winter and lower in autumn/summer and a large day-to-day variability. In this study, in order to forecast the total column ozone over Ankara, a multi-linear regression equation was performed. Predictors are selected by stepwise regression method. The ozone value on the previous day, temperature at the 100 hPa pressure level, previous day's temperature for the 700 hPa pressure level and temperature difference for 50 hPa and 500 hPa are the most important predictors. The success of monthly prognostic total column ozone models built up for Ankara is tested by using Brewer MK III Spectrophotometer data and satellite (OMI) data with the upper-air data in 2007. The Brewer MKIII has been in operation since November 2006 in Ankara. The ground-based one-year data show good agreement with the satellite OMI data.     

SCIAMACHY/Envisat,OMI/Aura,and ground-based total ozone measurements over Kyiv-Goloseyev station

Validation of satellite ozone measurements is important for data improvement due to instrumental long-term drifts and retrieval algorithm limitations. For satellite data quality estimation, we compare the total ozone content (TOC) derived from the satellite Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY)/Envisat and Ozone Monitoring Instrument (OMI)/Aura spectrometer overpass data and the ground-based measurements made with the Dobson spectrophotometer 040 at the GAW station No. 498 Kyiv-Goloseyev. The station was opened for Dobson ozone measurements in 2010. The results for Direct Sun, Zenith Blue, and Zenith Cloud observations are presented separately, in order to assess the influence of weather conditions (clear or cloudy sky) on the difference between satellite and ground-based measurements. Results from the SCIAMACHY–Dobson and OMI–Dobson difference analyses show small relative overestimation of TOC for satellite data. The ground-based Dobson 040 data are of high quality for Direct Sun and Zenith Blue from AD ((305.5 and 325.0 nm) and (317.5 and 339.9 nm)) pair measurements. Seasonal variations of the difference are seen with maximal satellite–Dobson data discrepancy near the winter solstice. Satellite TOC values are systematically higher than Dobson ones at solar zenith angles larger than 70°. This difference could be explained by seasonal non-uniformity in the satellite data.     

Recent trends of the total column ozone: implications for the Mediterranean region

The daily ozone column amounts during the 14-year period (1979–1992), which are inferred from measurements made with both the Total Ozone Mapping Spectrometer (TOMS) mounted on board the Nimbus-7 satellite have been used to study longitudinal trends at mid-latitudes. The main findings are: (1) There is a large longitudinal variation of the monthly trend in total ozone over the northern mid-latitudes ranging from 1.5 to 8.5 per cent per year with a large standard error, (2) The trend in the total ozone content over the Mediterranean area varies in a similar way with the zonal average total ozone trend over mid-latitudes. Also, the trend of the total ozone over Athens, Greece, is representative of the whole Mediterranean region and so it is representative of the zonal average total ozone trend over the northern mid-latitudes, and (3) The interannual variability of the amplitude of the annual wave in the total ozone amount over the Mediterranean region compares extremely well with the interannual variability of the total ozone amount over this location.     

Ozone depletion over Scotland as derived from Nimbus-7 TOMS measurements

The TOMS (Total Ozone Mapping Spectrometer) flown on the Nimbus-7 satellite has been measuring the total ozone concentration over the globe since November 1978. Recent investigations based on TOMS data have shown that in the latitude belt 40–70° N the spring ozone depletion rate reaches the value of —0·8 per cent per year. This paper reports trends derived from the TOMS reprocessed total ozone data for the case of Dundee (56·5°N, 3°W) from January 1979 to January 1992. The depletion rate of the mean monthly total ozone concentration over this 13-year period shows a strong variation from more than —15 per cent in December and January to about +0·5 per cent in February and June, while the overall mean is about —7 per cent.     

Global validation of FY-3A total ozone unit (TOU) total ozone columns using ground-based Brewer and Dobson measurements

Analysis of the accuracy and variability of total ozone columns (TOC) has been conducted by many studies, while the TOC observations derived from the total ozone unit (TOU) on board the Chinese FengYun-3A (FY-3A) satellite platform are notably less well documented. Therefore, in this present study, we mainly focus on the global-scale validation of TOU-derived total ozone column data by comparing them with spatially and temporally co-located ground-based measurements from the well-established Brewer and Dobson spectrophotometer for the period July 2009 through December 2011. The results show that TOU-derived total ozone column data yields high accuracy, with the root mean square error less than 5% in comparison with ground-based measurements. Meanwhile, TOU underestimates Brewer measurements by 1.1% in the Northern Hemisphere and overestimates Dobson total ozone 0.3% globally. In addition, TOU-derived total ozone shows no significant dependence on latitude in comparison with either Brewer or Dobson total ozone measurements. Nevertheless, a significant dependence of TOU-derived total ozone is observed on the solar zenith angle (SZA) in comparison with both Brewer and Dobson, demonstrating that TOU underestimates at large SZA and overestimates at small SZA. Finally, the dependence of satellite – ground-based relative difference for total ozone values shows fair agreement when total ozone values are in the range 250–450 Dobson units (DU). Overall, the Chinese FY-3A/TOU performs well on total ozone retrieval with high accuracy, and the total ozone data derived from the TOU can be used as a reliable data source for ozone monitoring and other atmospheric applications.     

Intercomparison of ozone models derived by remote and in situ sensing techniques with recent local measurements at middle latitudes

In the framework of the European Arctic Stratospheric Ozone Experiment (1991–1992) a scries of balloon ascents for ozone and temperature in situ measurements up to 35 km height have been performed at Athens, Greece (38° N, 24° E). This is the first time that such an intensive sounding campaign has been performed in Athens. The data collected for the vertical distribution of ozone and temperature have been compared with the satellite-derived reference models which provide the monthly latitudinal variations of vertical structure of both ozone and temperature. The comparison shows that at the middle stratosphere there is very good agreement between the Satellite Reference Model and the in situ ozone measurements. There is also very good agreement between the Satellite Reference Model and the in situ temperature measurements, thus confirming the recently published findings by Varotsos and Helmis.     

Mapping solar ultraviolet radiation from satellite data in a tropical environment

This paper presents a technique for mapping erythemally-weighted solar ultraviolet (EUV) radiation from satellite data in a tropical environment. A satellite-based EUV radiation model was formulated for calculating the EUV daily dose from satellite-derived earth-atmospheric albedo, total column ozone and other ground-based ancillary data. The earth-atmospheric albedo was obtained from a geostationary satellite (GMS5) while the total column ozone was retrieved from a polar orbiting satellite (EP/TOMS). The model was validated against the monthly average EUV daily dose from the measurements at four solar radiation monitoring stations located in the tropical environment of Thailand. The monthly average EUV daily dose calculated from the model was in reasonable agreement with that obtained from the measurement, with root mean square difference (RMSD) and mean bias difference (MBD) of 12.3% and 0.7%, respectively. After the validation, the model was used to calculate the monthly average EUV daily dose over Thailand employing an 8-year period of data from GMS5, EP/TOMS and other ancillary surface data. Values of the monthly average of EUV daily dose were presented as monthly and yearly maps. These maps reveal that the tropical monsoons have a strong influence on the EUV in this region.     

Annual,semi-annual and terannual waves in total ozone as derived from TOMS data at the subtropics

The reprocessed daily total ozone measurements made by the Total Ozone Mapping Spe trometer (TOMS) on Nimbus-7 over Athens (37·9° N, 23·8°E) have been analysed from January 1979 to January 1992. Monthly total ozone data are first estimated for the entire time period and are then Fourier analysed to obtain the amplitude, phase and percentage contribution to the total variance of the first, second and third harmonics. Findings presented in this paper concern the recent results in the literature according to which the northern mid-latitude total ozone trend shows a maximum seasonal cycle reaching greater than 0–8 per cent per year of ozone depletion in late winter.