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.     

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.     

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.     

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.     

On the correction of the total ozone content over Athens,Greece as deduced from satellite observations

The observations with the Total Ozone Mapping Spectrometer ( TOMS) mounted aboard the Nimbus-7 satellite have previously been used to determine the trends of the total ozone amount over Athens, Greece ( 38° N, 24° E), since 1979, for various months ( Varotsos, C. A., and Cracknell, A. P., 1993, International Journal of Remote Sensing, 14, 2053–2059). The total ozone depletion over the 13-year time period showed a strong seasonal variation of the trend from more than 7 per cent in winter to about 2·5 per cent in summer. However, the TOMS instrument measures the back-scattered ultraviolet radiation in order to determine ozone content and is limited to observations above the cloud level. ln the presence of thick cloud the column ozone content is generally underestimated. This underestimation of the total ozone amount is quantitatively examined, especially in the synoptic cases where ozone-rich air has been transported into the lower troposphere. The influence of this underestimation on the total ozone depletion over Athens, Greece, deduced from TOMS observations, is finally attempted.     

Variation of total column ozone along the monsoon trough region over north India

This study examined the total column ozone (TCO) variations over New Delhi (28.65° N, 77.217° E) and Varanasi (25.32° N, 83.03° E), which lie along the monsoon trough region, and over the tropical station Kodaikanal (10.23° N, 77.46° E), which lies outside the monsoon trough. Monthly, seasonal and annual TCO variations were determined using data from ground-based Dobson spectrophotometers during 2000–2008, Brewer spectrophotometers during 2000–2005 and the satellite-based Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) during 2002–2008. We found that Dobson, Brewer and SCIAMACHY TCO variations showed negative trends, indicating a decreasing tendency during the period studied at all three stations. Over Varanasi, the trend decreased further by about 3 DU year^?1. Quasi-Biennial Oscillation (QBO) influences were seen in the time series of TCO over New Delhi and Varanasi, and weaker QBO signals over Kodaikanal. Comparisons were made between ground-based Dobson and Brewer spectrophotometer and SCIAMACHY satellite monthly mean TCO values. The differences between SCIAMACHY and Dobson TCO were 0.4–4.2% for New Delhi and 2.3–6.2% for Varanasi. The differences between SCIAMACHY and Brewer TCO values were 2.0–6.4% for Kodaikanal. In the peak monsoon months (July and August), decreases in TCO values over New Delhi and Varanasi (the monsoon trough region) may be due to the deep convection present during the monsoon season. During the monsoon season, several intense cyclonic systems appear over the monsoon trough region and may cause lowering of the TCO. Kodaikanal shows opposite features, with high values being observed during the peak monsoon months. TCO values over New Delhi were found to be higher than those over Varanasi and Kodaikanal, and TCO values over Varanasi were higher than over Kodaikanal. It was concluded that TCO values increase with increasing latitude.     

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.     

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.     

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.     

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.     

Total ozone depletion over Greece as deduced from satellite observations

The reprocessed (version 7) daily total ozone observations made by the Total Ozone Mapping Spectrometer (TOMS) on the Nimbus-7 satellite over Athens (37.6 N, 23.4 E) for the period from November 1978 until April 1993 have been used to investigate total ozone depletion. To estimate the trends in total ozone content a linear fitting to the data has been applied, given that the other components like the quasi-biennial oscillation, the El Nino/Southern Oscillation and the solar cycle have a very small contribution to the total ozone depletion effects over that geographical region. The total ozone depletion over the 15-year period was derived from version 7 shows a strong seasonal variation from more than 6% in winter and early spring to about 1.5% in summer. The total ozone depletion over Greece is found to be about 1% (per decade) less using version 7 than using version 6.     

Intercomparison of satellite and ground-based measurements of ozone,NO2, HF,and HCl near Saint Petersburg,Russia

Regular intercomparison of different observing systems is a part of their testing and validation protocol, which gives the estimates of real measurement errors. The main objective of our study is the comparison of satellite and ground-based measurements of atmospheric composition near Saint Petersburg, Russia. Since early 2009, high-resolution Fourier Transform Infrared (FTIR) solar absorption spectra have been recorded at Peterhof station (59.82° N, 29.88° E), located in the suburbs of Saint Petersburg. We derived column amounts of O₃, HCl, HF, and NO₂ from these spectra using the retrieval codes SFIT2 and PROFFIT. We compared the data retrieved from Bruker 125 HR FTIR measurements with coincident satellite observations of the Microwave Limb Sounding (MLS), Ozone Monitoring Instrument (OMI), Fourier Transform Spectrometer from Atmospheric Chemistry Experiment (ACE-FTS), Global Ozone Monitoring Experiment (GOME and GOME-2), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instruments. The relative differences in ozone columns of FTIR from OMI-TOMS amount within (+3.4 ± 2.9)%, from GOME-2 are (+2.2 ± 3.0)%. The comparison of FTIR and MLS measurements of stratospheric ozone columns gives no mean and 5% of the RMS differences. Measurements of NO₂ columns agree with the mean difference of +9% and the RMS differences within 14–16% for FTIR vs. GOME-2, SCIAMACHY, and OMI. FTIR vs. GOME comparison gives (+6 ± 31)%. HCl columns comparison for FTIR vs. MLS shows ?4.5% in the mean and 12% in the RMS differences. FTIR vs. ACE-FTS comparison (nine cases) gives ?8% and 10% for the mean and the RMS relative differences, respectively. Comparison of HF columns shows (?12 ± 6)% and (?12 ± 11)% for FTIR vs. ACE data v.2.2 and v.3.0, respectively. These figures show that the Peterhof ground-based FTIR measuring system can be used to support the validation of satellite data in the monitoring of stratospheric gases.     

Impact of zonal wind on latitudinal variation of total columnar ozone over the Indian Peninsula

Latitudinal and seasonal variability of total columnar ozone from September 2007 to August 2008 across the Indian longitude sector within 10.5° N to 34.5° N and 70.5° E to 94.5° E using satellite data obtained from Aura Ozone Monitoring Instrument (OMI) of National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) is presented. The total column ozone (TCO) over the area of study shows a gradually varying pattern throughout the year. In the post-monsoon (autumn) and winter months, maximum TCO is observed in the north-western part of the subcontinent while the minimum is often observed towards the east at about the same latitudes. A west–east spatial gradient is clearly observed in autumn months. As winter approaches, a north–south spatial gradient becomes more prominent than the east–west gradient. It has been further observed that TCO does not vary significantly over the entire subcontinent in monsoon.     

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.     

Characterization of aerosols and pre-cursor gases over Maitri during 24th Indian Antarctica Expedition

Within the framework of the 24th Indian Antarctica Expedition (IAE), observations of total column aerosol optical depth (AOD), ozone (TCO) and precipitable water content (TCW) using a multi-channel solar-radiometer (MICROTOPS-II: Microprocessor-controlled Total Ozone Portable Spectrometer-II), and observations of short-wave global radiative flux using a wide-band pyranometer have been carried out over the Indian Antarctica station Maitri (70.76° S, 11.74° E) and the southern Indian Ocean during December 2004–February 2005. These extensive datasets have been utilized to investigate the aerosol optical, physical and radiative properties, and their interface with simultaneously measured gases. Data over the Oceanic region have been collected from the ship front deck. The daily mean AOD at a characteristic wavelength of 500 nm was found to be 0.042 with an average Angstrom coefficient of 0.24, revealing an abundance of coarse-mode particles. Interestingly, the January fluxes were found to be less by about 20% compared with those in February. The average short-wave direct radiative forcing due to aerosols showed cooling at the surface with an average value of??0.47 Wm^?2. The TCO increased from about 252 DU around 38° S to about 312 DU at 70° S, showing a gradual increase in ozone with increasing latitude. The TCO measured by the surface-based ozone monitor matched reasonably well with that observed by the Total Ozone Mapping Spectrometer (TOMS) satellite sensor within 5%. Variability in ozone on a daily scale during the study period was less than 4% over the Antarctica region.     

Ozone dynamics over Greece as derived from satellite and! in situ measurements

A comprehensive analysis of the records of surface ozone available for Athens, Greece ( 38° N, 24° E) for the periods 1901–1940 and 1987–1990 is presented. Both records are analysed to explore the intraseasonal fluctuations and the harmonic components of surface ozone and also compared to other historical surface ozone records. The variation in surface ozone concentration during rainfall is also investigated, using the hourly measurements of the surface ozone concentration obtained by a network of four stations within the Greater Athens area. The results indicate that, during rainfall events which are associated with the passing of a cold front, an important decrease of the surface ozone concentration is observed. Daily measurements of surface ozone and NO_x, from five stations in the Greater Athens Basin overthe period 1986–1990 are also used in order to examine the main features of basin-wide 0₃-HC-NO_x relations. A simple regression model between the surface ozone concentration and the temperature at the 850 hPa level, which was first tested in Los Angeles, gave satisfactory results in reproducing the mean monthly ozone variation in Athens, when coefficients extracted from local data were used in the regression equation. A series of vertical ozone soundings over Athens has been also performed in order to explore the tropospheric ozone variations and to examine further the transport that occurs at the 700hPa level with advection from the north-western sector. The relevant results are discussed. The existing uncertainties concerning the stratosphere-troposphere exchange of ozone which mainly occurs during midlatitude tropopause folding as well as during cut-off low events are also discussed. The examination of the role of the atmospheric circulation in the lower stratosphere in relation to the laminated structure of ozone is also attempted. 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. 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. We have also used total ozone measurements obtained with a Dobson spectrophotometer ( No. 118) which has been instituted in Athens from 1989 in order to examine the consistency of data from TOMS with the corresponding Dobson data on a daily basis. Furthermore monthly mean total ozone data were first estimated for the entire period and were then Fourier analysed to obtain the amplitude, phase and percentage contribution to the total variance of the first, second and third harmonics.     

Improvement of the Umkehr ozone profile by the neural network method: analysis of the Belsk (51.80°N, 20.80°E) Umkehr data

Vertical profiles of atmospheric ozone by the neural network (NN) method are compared with those obtained by the standard Umkehr inversion algorithm – UMK92. Both methods used the same input, the so-called N values, derived from Umkehr measurements at Belsk (51.80°N, 20.80°E), Poland, by the Dobson spectrophotometer No 84. The vertical profiles of ozone from satellite observations, Microwave Limb Sounder (MLS) overpasses for the period 2004–2009, and from ozonesoundings performed at the nearby aerological station, Legionowo (52.4° N, 21.0° E), for the period 2000–2009 provide a reference data set for the NN model building. The NN methodology appears to be a promising tool for extracting information about the vertical ozone profile from ground-based Umkehr measurements, despite some limitations of the NN method itself, such as the results being limited to the analysed station, sensitivity to errors in the reference data sets, and lack of possibility to determine the actual retrieval errors. Accuracy of the NN ozone profiles is better for all Umkehr layers than that by the standard Umkehr inversion algorithm when NN and UMK92 profiles are compared with the reference profiles. It is especially pronounced for comparisons with the ozonesonde profiles for layers 4 and 1, where the absolute error changes from 10.6 Dobson units (DU) (UMK92) to 4.4 DU (NN) and from 6.6 DU (UMK92) to 3.5 DU (NN), respectively (1 Dobson unit is equal to 2.69 × 10²⁰ molecules/m²). The mean (over all Umkehr layers) correlation coefficient between NN-MLS, and NN-ozonesonde profiles is 0.75 and 0.85, respectively. The corresponding correlation coefficients for the comparison with UMK92 profiles are lower, i.e. 0.61 and 0.64, respectively.     

Total ozone amount trend at St Petersburg as deduced from Nimbus-7 TOMS observations

The observations of the Total Ozone Mapping Spectrometer (TOMS) flown on the Nimbus-7 satellite have been used in order to detect the monthly trend in total ozone concentration over St Petersburg (60°N, 30°E) during the period from November 1978 to January 1992. The trend analysis suggests that the total ozone depletion over the 13-year period shows strong variations from month to month reaching —13 per cent for December but with a slightly positive trend for September.     

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.     

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.