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.     

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.     

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.     

A note on the comparison between total ozone from Oslo CTM2 and SBUV satellite data

The results of a comparison between total ozone amounts derived from solar backscatter ultraviolet (SBUV) satellite observations and those calculated from the chemical transport model Oslo CTM2 are presented for the period 2001–2007. Monthly mean total ozone amounts from improved model simulations were used to compute monthly, seasonal and annual zonal means over 10° latitude zones, and compared with respective satellite retrievals over the northern and southern hemispheres. The results show that the improved model simulations slightly underestimate total ozone over the northern hemisphere when compared with the satellites by 1.4% on average, and slightly overestimate total ozone over the southern extra-tropics, middle and high latitudes by 1.6% on average. The mean difference between the model- and satellite-derived total ozone columns from 75°S to 75°N is estimated to be about ?0.3%. A linear regression analysis between the model- and satellite-derived total ozone data shows statistically significant correlations between the two data sets at all latitude zones (about +0.8 in the tropics and more than +0.9 over all other latitudes). The annual cycle of total ozone is shown to be well reproduced by the model at all latitudes.     

Long-term trends of total ozone content over mid-latitudes of the Northern Hemisphere

Dynamic climatic normals and long-term trends of total ozone in the mid-latitudes of the Northern hemisphere (30°N–60°N) have been determined using data from satellite observations for the period of 1978–2017. The annual course of total ozone is shown as changing over the various regions during the period of observations. The specific features of alteration in the state of the ozone layer are discussed depending on latitude and longitude. Thus, a general increase in total ozone in winter, an increase in spring (with the exception of the northern latitudes of Europe, Asia, and Pacific), and a continuing decrease in summer (with the exception of the northern latitudes of America) during the last 17 years is revealed. The long-term trends of total ozone for different regions and latitude zones (30°N–40°N, 40°N–50°N, and 50°N–60°N) are given depending on season.     

Prediction of mean monthly total ozone time series – application of radial basis function network

The primary objective of the present paper is to apply Artificial Neural Network in the form of Radial Basis Function network to predict the mean monthly total ozone concentration over Arosa, Switzerland (46.8° N/9.68° E). The satellite observations of the total ozone content are based on the total ozone observations performed by the ground‐based instrumentation. While analysing the dataset it was found that January, February and March are the months of maximum variability in the mean monthly total ozone over the stated region. Then, these three months were considered as the target months to frame the predictive model. After appropriate training and testing, it was found that Radial Basis Function network is a suitable neural net type for predicting the aforesaid time series. Moreover, this kind of neural net was found most adroit in predicting the mean monthly total ozone in the month of January.     

A probe into the chaotic nature of total ozone time series by correlation dimension method

The endeavor of the present paper is to investigate the existence of chaotic behavior in the underlying dynamics of the total ozone concentration over Arosa, Switzerland (9.68°E, 46.78°N). For this purpose, the correlation dimension method is employed to the mean monthly total ozone concentration data collected over a period of 40 years (1932–1971) at the above location. Based on the observation of a low correlation dimension value of 1 for this data set, the study reports the existence of low-dimensional chaotic behavior in the ozone concentration dynamics.     

Optical monitoring of characteristics of the stratospheric aerosol layer and total ozone content at the Siberian Lidar Station (Tomsk: 56° 30′ N; 85° E)

We consider the results of long-term remote optical monitoring obtained at the Siberian Lidar Station of Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, Tomsk (56° 30′ N, 85° E). The scattering characteristics of stratospheric aerosol layer, obtained according to data of lidar measurements recorded since 1986, are presented. We analyse the trends of changes in the total ozone (TO) content over Tomsk for the period 1996–2013 according to data of spectrophotometric measurements employing Total Ozone Mapping Spectrometer (TOMS) data for the period 1979–1994. We determined the periods of elevated content of stratospheric aerosol over Tomsk after a series of explosive eruptions of volcanoes in the Pacific Ring of Fire and Iceland in 2006–2011. Since the second half of the 1990s we have recorded an increasing TO trend, equalling 0.65 DU/year for the period 1996–2013.     

Extremes in total ozone content over northern India

Using daily station total ozone data from TOMS on Nimbus‐7 (1979–1993) and Earth Probe (1997–2005) satellites of National Aeronautics and Space Administration (NASA)/Goddard Space Flight Center (GSFC) during the period 1979–2005, the characteristic features of extremes in the total ozone content and the frequency of the low/high ozone days have been carried out over the northern parts of India in the winter season. Stations located in the north of 20° N latitude regions of India have been chosen for the study. To determine whether the day is a low, high or normal ozone day, the statistical percentile thresholds are computed based on the daily data during winter months (January and February). It has been observed that the trends in the frequency of low ozone days are increasing and for the high ozone days are decreasing during 1979–1993. Similarly the trends in the highest total ozone reaching during January and February are decreasing. The recent period (1997–2005) shows opposite trends that are not statistically significant or stable during the period. Even the mean total ozone during January and February for the period 1979–1993 show the decreasing trends. Overall the trends in the total ozone extremes and the frequency of low/high ozone days are found to be decreasing over the northern parts of India during the winter season.     

Roles of ozone depleting substances and solar activity in observed long-term trends in total ozone column over Indian region

An additive time-series decomposition analysis was performed on the Multi Sensor Reanalysis-2 (MSR-2) monthly mean total ozone column (TOC) time-series dataset spanning over 34 years (January 1979–December 2012) for Indian region (0.0–40.0 °N; 67.5–97.5° E). Statistically significant (p-value <0.05) long-term trends in TOC were estimated in the deseasonalized TOC time series. The role of multiple natural and anthropogenic factors: quasi biennial oscillations (QBO), El-Nino Southern Oscillations (ENSO), cyclic variation in solar activity (SA), and ozone depleting substances (ODS) was investigated to explain the long-term trends in TOC over Indian region. Over sub-tropical Indian region (25.0° N– 40.0° N), declining long-term linear trends were estimated, which varied from ?0.30% to ?1.10% per decade. Interestingly a positive long-term linear-trend (0.10–0.30% per decade) was observed over equatorial-tropical part of Indian region. No statistically significant long-term trend was observed for 30mb Equatorial Zonal Winds and Nino 3.4 index – indicators for QBO and ENSO; however, a positive long-term linear trend of magnitude 17.00 ± 1.18% per decade was observed in effective equivalent stratospheric chlorine – a proxy for ODS, and a negative long-term linear trend of magnitude 12.72 ± 2.86% per decade was observed in 10.7 cm Solar Radio Flux – a representative for SF. It is inferred that over the Indian region above tropic of cancer, about 85.00% of the estimated negative long-term linear trend in TOC can be explained by the increase in the stratospheric concentration of ODS; whereas, decrease in the solar activity accounted for 15.00% of the estimated negative long-term linear trend in TOC over sub-tropical Indian region.     

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.     

Annual anomalies and trends for TOMS reflectivities (1978–2005) in the Southern Hemisphere

Annual anomalies of Lambertian equivalent reflectivity (LER) retrieved from the total ozone mapping spectrometer spanning the period November 1978–November 2005 were studied in the Southern Hemisphere, in a region bounded by 0° S and 60° S, and their trends were estimated. With the exception of few regions where the variable may represent the contribution of both cloudiness and snow, trends in LER anomalies provided an evolution of total cloudiness. On average, the study region experienced a net increase in LER values of 0.78 reflectivity units (RU) decade^?1; if only significant trend values are considered this figure increased to 1.18 RU decade^?1. The region that showed the largest upward trend, up to 4 RU decade^?1, was located over the eastern Pacific, off the coasts of Chile and Peru, where the presence of marine stratocumulus is frequent. Despite the overall positive trend there were regions that yielded a negative one, most notably the tropical latitudes of South America and Africa. The yearly zonal means also showed a positive trend at all latitudes, but significance occurred beyond 20° S only. Correlation maps between LER anomalies and five different circulation indices were also introduced. The indices with the highest and lowest number of significant correlation values were the Madden–Julian oscillation at 70° E and the quasi-biennial Oscillation, respectively.     

Effects of zonal wind on stratospheric ozone variations over Nigeria

The effects of zonal wind on stratospheric ozone (O₃) variation over Nigeria have been studied. The areas covered in this study include: Maiduguri (11.83° N, 13.15° E), Ikeja (6.45° N, 3.40° E), Port-Harcourt (4.75° N, 7.00° E), Calabar (4.95° N, 8.33° E), Makurdi (7.73° N, 8.54° E), Ilorin (8.50° N, 4.55° E), Akure (7.17° N, 5.08° E), Yola (9.23° N, 12.46° E), Minna (9.61° N, 6.56° E), Jos (9.93° N, 8.88° E), Kano (12.00° N, 8.52° E), and Enugu (6.45° N, 7.51° E), from 1986 to 2008. Zonal wind data was computed from the iso-velocity map employing Matrix Laboratory (MATLAB) software. The mean monthly variations of atmospheric angular momentum (AAM) and length of day (LOD) at pressure levels of 20, 30, and 50 mbar in the atmosphere mostly depict a trend of maximum amplitude between April and September, and minimum amplitude between December and March. The trend observed in seasonal variation of column ozone data in the low latitude had maximum amount from May through August and minimum values from December through February. The mean monthly maximum O₃ concentrations was found to be 284.70 DU occurring at Kano (12.00° N, 8.52° E) in May 1989 while an average monthly minimum O₃ concentration was found to be 235.60 DU occurring at Port-Harcourt and Calabar (4.75° N, 7.00° E and 4.95° N, 8.33° E, respectively) in January 1998. It has been established in this study that the variation in LOD caused by AAM mostly transfer O₃ by means of zonal wind from the upper troposphere to the lower stratosphere in the stations under study. The strong effect of the pressure levels of the atmosphere on O₃ variation could be attributed to its effect on the AAM and LOD. Variation in the LOD is significant in the tropics, suggesting that the effects of the extra-tropical suction pump action are not the only driver responsible for O₃ transportation from the tropics to extra-tropical zones. Analyses show a relationship with strong correlation between rainfall intensities and total ozone throughout the year under study. For instance, the obtained value of r ranges between 0.676 and 0.957 and p-value <0.05. This most likely indicates that the phenomenon could probably contribute to total ozone variations in Nigeria. Consequently, these findings lead to a deduction that weather pattern alteration observed due to these changes could lead to climate change.     

Zenith scattered light measurement: observations of BrO and OClO

Stratospheric BrO and OClO observations have been made for the first time over a tropical station, Pune (18° 31′ N, 73° 55′ E) using a Differential Optical Absorption Spectroscopy (DOAS) technique by measuring zenith sky scattered light spectra in the wavelength range of 346–358 nm by ultraviolet (UV)/visible spectrometer. The Differential Optical Density (DOD) fitting technique is applied for the right selection of a suitable spectral region for the analysis to minimize interference and poorly fitting absorption features, and also to minimize the residual of the fit. Observed DODs of O₃, NO_2, BrO, OClO, O₄, Rayleigh and Ring are well fitted with the calculated DODs and the percentage DODs are found to vary up to 0.5%, 0.8%, 0.15%, 0.13%, 1.5%, 1.2% and 1.3% respectively. Chlorine and bromine species play an important role in the ozone depletion, hence O₃, NO₂, BrO and OClO Slant Column Densities (SCDs) are derived between 76° and 94° Solar Zenith Angles (SZAs). The SCDs of O₃ are found to be decreased in the twilight period (i.e. between 90° and 94° SZA) in the presence of sufficient BrO and OClO. Total Column Densities (TCDs) of O₃, NO₂, BrO and OClO are derived by UV/visible spectrometry, Brewer spectrometry and satellite-based Scanning Imaging Absorption spectrometer for Atmospheric Cartography (SCIAMACHY) for Pune and the higher latitude station Kanpur (26° 28′ N, 80° 24′ E) during the period 1 April–31 June 2008. The day-to-day variations in O₃ and NO₂ TCDs over Pune are found to be more than over Kanpur. BrO TCDs vary between 1.9?×?10¹³ and 4?×?10¹³ molecules cm^?2 over Pune, which are derived by UV/visible spectrometry, while they vary for the high-altitude station Kanpur between 0.5?×?10¹³ and 3.5?×?10¹³ molecules cm^?2 derived by SCIAMACHY. The OClO TCDs are found to have an increasing trend with variations between 2?×?10¹³ and 4.5?×?10¹³ molecules cm^?2 during the above period.     

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.     

A study of spatial and temporal dynamics of total ozone over Southwest China with multi-source remote-sensing data

This article describes a study of the spatial and temporal dynamics of total ozone over Southwest China using satellite-retrieved total ozone products from 1996 to 2008 and a ground-based Dobson spectrophotometer. The findings indicated that the value of total ozone (265.7 Dobson unit (DU)) over Southwest China is lower than the value (273.7 DU) over the adjacent region at the same latitude by about 8 DU, and is about 13.8 DU lower than the global average at the same latitude (279.5 DU), and that there is a distinctly low-value area due to the higher elevation. The relationship of total ozone and the elevation presents a negative correlation, the terrain being the main factor to affect this condition. In the long term, the variation of total ozone exhibits a slightly increasing trend from 1996 over this region. Total ozone presents an obvious seasonal change, with the largest value appearing in springtime and the smallest appearing in wintertime. The difference between the regional seasonal mean value of total ozone in springtime and wintertime is about 28 DU, although the difference between the maximum and minimum monthly total ozone throughout a year is up to 50 DU. There is a positive correlation between the variation of total ozone and relative humidity. Relative humidity may be an important factor impacting on the pattern of seasonal change of total ozone.     

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.     

Assessment of total columnar ozone climatological trends over the Indian sub-continent

In the present study, long term satellite and Dobson spectrophotometer Total Column Ozone (TCO) data have been used to study the interannual variability and also to assess climatological trends in TCO over different geographical locations of Indian sub-continent. TCO data were analyzed for the period 1957 to 2015 over New Delhi (28.63° N, 77.18° E), Varanasi (25.30° N, 83.02° E), Pune (18.53° N, 73.84° E) and Kodaikanal (10.0° N, 77.47° E). An extensive validation was performed for Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instrument (OMI) retrieved TCO data independently with Dobson Spectrophotometer TCO measurements over New Delhi, Varanasi, Pune and Kodaikanal. The results of this exercise showed good correlation coefficient (r) of 0.87 (0.88), 0.84 (0.82), 0.91 (0.80) and 0.84 (Data not available) respectively. Climatological mean TCO over New Delhi, Varanasi, Pune and Kodaikanal are 275.02 ± 6.44 DU, 269.03 ± 7.34 DU, 260.78 ± 5.07 DU and 258.71 ± 6.36 DU respectively for the period 1957 to 2015. An increasing trend over New Delhi (0.20 DU year^–1), Pune (0.18 DU year^–1), Kodaikanal (0.14 DU year^–1) and decreasing trend over Varanasi (0.01 DU year^–1) were observed. High significance of TCO trend was found at New Delhi (p-value < 0.0001), Pune (p-value = 0.002) and Kodaikanal (p-value = 0.003) with negligible trend over Varanasi with p-value of 0.84. The TCO variations at different geographical locations associated with upper atmospheric meteorological parameters such as lower Stratospheric Temperature (ST) at 65 hPa and Tropopause Height (TH) were also addressed. Annual lower stratospheric temperature shows positive relationship with TCO and Stratospheric ozone over the study sites. Further, decadal variability in TCO with respect to solar activity at New Delhi was also analyzed.     

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.     

Surface and total ozone investigations in the region of Sofia,Bulgaria

Atmospheric ozone behaviour over Sofia has been investigated with remote-sensing and in situ techniques. Surface ozone and boundary layer observations performed in recent years at three city sites have been analysed. It was found that, in the autumn period, at close meteorological conditions, diurnal ozone variations show stable behaviour from year to year during the analysed period. It may be assumed that the boundary layer and ozone precursor concentrations, which are involved in photochemical ozone formation, keep up their state from year to year at the mentioned conditions. These findings may be interesting when surface ozone trends and climate change influence on ozone are investigated. The analysis of the long-term total ozone content (TOC) variations did not find a total ozone trend in the 1997–2008 period.