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From 1979 to 2006, the Red Sea trough (RST) in spring was objectively detected and classified into three categories (short, moderate and long) depending on its northward extension. The results indicated that most short RSTs appeared during a cold spring (larger by 7% in March than May), while most long RSTs appeared during a warm spring, where reached 71.7% in April and May. The dust events during the study period were identified using a threshold value of the Total Ozone Monitoring Satellite (TOMS) aerosol index (AI). The identified dust cases were used to classify each RST category into two classes, dust RSTs and non-dust RSTs. The synoptic characteristics of the RSTs associated with dust events that influenced the northern and western Arabian Peninsula (AP) were studied using each dust category (i.e., comparing dust and non-dust cases) and were compared between the different categories (i.e., comparing the dust cases among short, moderate and long categories). The synoptic study shows that the condition favorable for transporting dust westward into the AP occurs when an interaction is produced between the low pressure over the southern AP and Sudan low and forms a wavy zonal pressure gradient. When the RST is relatively strong, i.e., the situation has a pronounced wavy zonal and meridional pressure gradient area, it produces conditions favorable for transporting dust around the Red Sea. Commonly, dust RSTs are atmospherically integrated systems with pronounced circulation (downward motion in the eastern AP and upward motion in the western AP), a vertical westward trough tilt, horizontal tropical–extratropical interactions and north–south orientations of pressure/geopotential isolines.

The paper studies seasonal and long-term variability of the number of positive and negative anomalies of total ozone (TO) for the whole globe, the Northern Hemisphere, Russia, and the latitude zone it belongs. Satellite data are used for the research. It is found that the long-term variability of TO is significantly higher than the seasonal one and is caused by the slowest tidal oscillation with a period of 18.6 years and by the parametric resonance with it. The analysis of the residuals of results of seasonal and long-term simulations for similarity to white noise demonstrates that other contributions to these values, if present, are significantly below the detection threshold for modern global monitoring tools.

Sixteen years (July 2003–July 2019) of ground-based measurements of total ozone in the urban environment of Athens, Greece, are analyzed in this work. Measurements were acquired with a single Brewer monochromator operating on the roof of the Biomedical Research Foundation of the Academy of Athens since July 2003. We estimate a 16-year climatological mean of total ozone in Athens of about 322 DU, with no significant change since 2003. Ozone data from the Brewer spectrophotometer were compared with TOMS, OMI, and GOME-2A satellite retrievals. The results reveal excellent correlations between the ground-based and satellite ozone measurements greater than 0.9. The variability of total ozone over Athens related to the seasonal cycle, the quasi biennial oscillation (QBO), the El Nino Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the 11-year solar cycle, and tropopause pressure variability is presented.

The variability of Arctic total ozone in the winter of 2015/2016 is studied using the data of the national network equipped with M-124 filter ozonometers and satellite monitoring. The first ozone mini-hole that emerged in the first half-year over the whole history of observations (developed at the end of January 2016) is analyzed. The reasons for the total ozone variability over Russia in the first quarter of 2016 are analyzed, and the comparison with the significant Arctic ozone anomalies in 1996/1997 and 2010/2011 is presented.

A regional climate change, as a long-term repeated weather regime typical for a specific area, has become one of the main themes in Climate Change (CC) research. Forecasting the possible climate changes requires knowledge of the variations of natural and anthropogenic climate-forming factors, understanding of the mechanisms that determine the response of the Earth’s climate system to these impacts. One of the factors influencing the regional climate is the total ozone content in the atmosphere. The aim of this article is to establish a correlation links between the total ozone content and the short-term regional climatic events. Presented analysis is based on data from orbital observations of the movement of ozone anomalies, data from different databases and researches of the National Ozone Monitoring Research and Education Center.

The main objective of the study is development a method for forecasting the state of ozone above the Ukrainian Antarctic Akademik Vernadsky station since 1972 are presented in the article.The result of study of the state of ozone above Vernadsky station from 1972 is given in the article. An analogue to the state of ozone 2016/2017 is found using the similarity criteria from the observations archive of the station. The proposed model of the change in large-scale atmospheric circulation for the Southern Hemisphere is used to predict the state of the ozone over the Vernadsky station in the next decade. Main conclusion from this study is that in the next decade should expect an increase in the total ozone above the station.

In this research, the climatological characteristics of total column ozone (ToZ) over Irene, South Africa (25.5o S, 28.1o E), are studied using both ground-based and satellite observations. Satellite data from the Total Ozone Mapping Spectrometer (TOMS) from November 1978 to May 1993; the Global Ozone Monitoring Experiment-1 (GOME-1) from August 1995 to June 2003; the Earth Probe Total Ozone Monitoring Spectrometer (EP-TOMS) from January 1997 to December 2005; the Microwave Limb Sounder from October 2004 to April 2013; the Ozone Monitoring Interferometer (OMI) from October 2004 to December 2013; the Global Ozone Monitoring Experiment-2 (GOME-2) from January 2007 to December 2013; and the Infrared Atmospheric Sounding Interferometer (IASI) from June 2008 to December 2011, were used in this study together with ground-based measurement from a Dobson instrument (August 1989 to December 2011). The seven satellite and ground-based instruments used for this study were selected as they provide long term ozone monitoring data. Satellite observations were collected when they overpass Irene and showed that ToZ replicated the expected behavior of spring maximum and autumn minimum. When compared with other satellite data sets, TOMS ToZ data displayed values approximately 8 DU higher overall but showed good general agreement with measurements from the ground-based Dobson instrument. The OMI instrument had the best agreement with the Dobson instrument as the measurements are within 5 DU for all seasons. The result of trend trend analysis of ozone over Irene shows a significant decrease of ~8 DU in total ozone from 1978 to 1993 with a gradual recovery and increase of ~2 DU in total ozone from 1995 to 2005 as measured by both GOME-1 and EPTOMS. An increase of approximately 7-9 DU is observed in measurements from OMI and IASI thereby illustrating the gradual recovery of the ozone layer. EPTOMS also showed good agreement with the Dobson instrument. GOME-1 and GOME-2 reveal underestimation of ozone while IASI overestimated ozone for the first half of the year. Between 1995 and 2005, both EPTOMS and GOME-1 data showed a gradual increase in column ozone of approximately 2 DU which has increased to approximately 7 DU in the last decade as measured by OMI, GOME-2 and IASI satellites. The result obtained showed a very strong correlation (~97%) between the variation in OMI-Dobson and GOME-2-Dobson and (~85%) between the variation in EPTOMS-Dobson and GOME-1-Dobson.

Considering the potential importance of the concentration of ozone in the atmosphere and threat to its depletion in Pakistan’s environment, AQUA-AIRS Level-3 Daily Global satellite data is used to monitor the Total Column Ozone (TCO) over the entire region of the country. During 2003–2011 with spatial resolution of 1ox 1o lat/long grid, inter-annual analysis of TCO over the area (62°-76°E and 23°-37°N) showed that overall average distribution of TCO alterations are dependent on latitude and varied from 275 to 278 DU in the regions of Sindh and Baluchistan province with 297–300 DU in the northern and KPK province regions. Seasonal variations have shown that in the region 23°-29°N, highest concentration of ozone is recorded in summer season (JJA) and lowest in winter season (DJF) with mixed trend in both spring (MAM) and autumn (SON) seasons whereas in the region between 30°-37°N, maximum is recorded in winter (DJF) and spring (MAM) seasons with minimum in summer (JJA) and autumn (SON) seasons respectively. Statistical analysis revealed that linear relationship exists between year to year TCO and solar activity.

A four-step adaptive ozone trend estimation scheme is proposed by integrating multivariate linear regression (MLR) and ensemble empirical mode decomposition (EEMD) to analyze the long-term variability of total column ozone from a set of four observational and reanalysis total ozone data sets, including the rarely explored ERA-Interim total ozone reanalysis, from 1979 to 2009. Consistency among the four data sets was first assessed, indicating a mean relative difference of 1% and root-mean-square error around 2% on average, with respect to collocated ground-based total ozone observations. Nevertheless, large drifts with significant spatiotemporal inhomogeneity were diagnosed in ERA-Interim after 1995. To emphasize long-term trends, natural ozone variations associated with the solar cycle, quasi-biennial oscillation, volcanic aerosols, and El Nino–Southern Oscillation were modeled with MLR and then removed from each total ozone record, respectively, before performing EEMD analyses. The resulting rates of change estimated from the proposed scheme captured the long-term ozone variability well, with an inflection time of 2000 clearly detected. The positive rates of change after 2000 suggest that the ozone layer seems to be on a healing path, but the results are still inadequate to conclude an actual recovery of the ozone layer, and more observational evidence is needed. Further investigations suggest that biases embedded in total ozone records may significantly impact ozone trend estimations by resulting in large uncertainty or even negative rates of change after 2000.

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

South America is one of the most vulnerable areas to stratospheric ozone depletion; consequently, an increased amount of UV radiation reaches the Earth’s surface in this region. In this study, we analyzed the long-term trend in the total ozone column (TOC) over the southern part of the South American continent from 1980 to 2009. The database used was obtained by combining several satellite measurements of the TOC on a 1° (latitude) × 1.25° (longitude) grid. Analysis of the long-term trend was performed by applying the Theil-Sen estimator and the Mann–Kendall significance test to the deseasonalized time series. The long-term trend was also analyzed over several highly populated urban zones in the study area. Finally, multiple linear regression (MLR) modeling was used to identify and quantify the drivers of interannual variability in the TOC over the study area with a pixel-by-pixel approach. The results showed a decrease in the TOC ranging from −0.3 to −4% dec−1 from 1980 to 2009. On a decadal timescale, there is significant variability in this trend, and a decrease of more than −10% dec−1 was found at high latitudes (1980–1989). However, the trends obtained over much of the study area were not statistically significant. Considering the period from 1980 to 1995, we found a decrease in the TOC of −2.0 ± 0.6% dec−1 at latitudes below 40° S and −6.9 ± 2.0% dec−1 at latitudes above 40° S, for a 99.9% confidence level over most of the study area. Analysis of the period from 1996 to 2009 showed a statistically significant increase of 2.3 ± 0.1% dec−1 at high latitudes (> 60° S), confirming the initial TOC recovery in the Antarctic. Despite evidence for initial recovery of the TOC in some parts of the study area between 1996 and 2009, the long-term increase from September to November is not yet statistically significant. In addition, large parts of the study area and most of the urban areas continue to show a decreasing trend in the TOC. The MLR results show that at high latitudes, the main driver of interannual variability in the TOC is the total effective amount of halogens, followed by the eddy heat flux.

We present the first analysis of the combined El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) contribution to the monthly zonal means of total ozone (TO3) in the Northern Hemisphere for the 1970–2015 period. The Solar Backscatter UV merged TO3 (version 8.6) data set is examined using the standard multiple regression model with new proposed regressors accounting for the impact of the strong ENSO and IOD effects on the zonal mean ozone. The new regressors are selected using the principal component analysis applied to the standard ENSO and IOD indices. The ENSO and IOD induce ±2% month-to-month TO3 oscillations in the equatorial-, mid-, and even in high latitudinal zones. Long-term effects of ∼1% 10 year−1 are found. In autumn, a strong positive phase IOD is associated with ∼0.5% positive and ∼1.5% negative anomalies in the 30°–35°N and 65°–70°N regions, respectively. The IOD contribution to the zonal TO3 means is more pronounced than that of ENSO.

This study analyzes the total ozone column (TOC) variability over the Iranian plateau (Esfahan) from 1978 to 2011. Results show that the annual average of TOC in Esfahan tends to decrease with time, which is strongly dependent on the season, with maximum values during the winter–spring months (more than 2.2 %/decade). By applying a defined threshold that includes the TOC monthly −2σ, it is found that the maximum occurrence of low ozone events (LOEs) tends to be more frequent in the second half of year with about four-fifth of the observed LOEs (last summer, autumn, and early winter). During two cases of LOE, the tropopause height (TH) was uplifted ~2–4 km with temperature of 10 °C colder than the long-term mean, and the synoptic pattern was characterized by high-pressure systems in UTLS region. The extreme LOEs were consistent with the horizontal transport of ozone-poor air toward the Iranian plateau and vertical advection in UTLS region. The former mechanism plays a primary role in formation of extreme LOEs based on the observed TOC reductions during previous days over the source regions (Sahara desert and Himalaya region). Day-to-day variations of maximum UV index during LOEs show that by a decrease in TOC ~14 %, while the aerosol optical depth (AOD) in the cloudless condition reach their lowest rates (lower than 0.3), UV radiation exceeds very high and extreme levels in late winter and mid-spring, respectively.

This study develops a proper way to incorporate Atmospheric Infrared Sounder (AIRS) ozone data into the bogus data assimilation (BDA) initialization scheme for improving hurricane prediction. First, the observation operator at some model levels with the highest correlation coefficients is established to assimilate AIRS ozone data based on the correlation between total column ozone and potential vorticity (PV) ranging from 400 to 50 hPa level. Second, AIRS ozone data act as an augmentation to a BDA procedure using a four-dimensional variational (4D-Var) data assimilation system. Case studies of several hurricanes are performed to demonstrate the effectiveness of the bogus and ozone data assimilation (BODA) scheme. The statistical result indicates that assimilating AIRS ozone data at 4, 5, or 6 model levels can produce a significant improvement in hurricane track and intensity prediction, with reasonable computation time for the hurricane initialization. Moreover, a detailed analysis of how BODA scheme affects hurricane prediction is conducted for Hurricane Earl (2010). It is found that the new scheme developed in this study generates significant adjustments in the initial conditions (ICs) from the lower levels to the upper levels, compared with the BDA scheme. With the BODA scheme, hurricane development is found to be much more sensitive to the number of ozone data assimilation levels. In particular, the experiment with the assimilation of AIRS ozone data at proper number of model levels shows great capabilities in reproducing the intensity and intensity changes of Hurricane Earl, as well as improve the track prediction. These results suggest that AIRS ozone data convey valuable meteorological information in the upper troposphere, which can be assimilated into a numerical model to improve hurricane initialization when the low-level bogus data are included.

The analysis of extreme events is an essential key in the research of the atmospheric ozone due to their importance in biological and radiative effects. Total ozone column (TOC) databases from five ground-based sites equipped with a Brewer spectrometer are used to evaluate extreme ozone events along the Iberian Peninsula for the period 2002–2012. The monthly standard deviation is proved as a reliable metric to identify extreme cases. A total of 465 events (days) are classified as extremes events. For the database used, 2011 presents 32 events with very low TOC values (miniholes), while 2010 is the year with the maximum number (51) of events with very high TOC values (minihighs). The weight of the miniholes (minihighs) over the ozone annual mean can achieve values over the 4% (8%). The relationship between global dynamical features and ozone extreme events is also addressed in this study. Double tropopause events have explained in 2002 and 2004 up to the half of minihole events, while the North Atlantic Oscillation (NAO) negative phase is the condition prevalent in the majority of the minihighs in the entire period. These global characteristics are verified in the analysis of a case study (February–March 2004) exhibiting two periods with double tropopause events and a change in the sign of the NAO index with the consequent change in the tropopause pressure.

This study focuses on multi-year change in Total Ozone Content (TOC) values measured simultaneously by ground based instrument, i.e., MICROTOPS-II sun photometer and space based TOMS satellite experiment during the last decade, i.e., the period from 2002 to 2009 in the outskirts of the semi-arid and semi-urban tropical region of Udaipur (24.6°N, 74°E; 580 m asl), India. The negative declining trend in TOC value has been detected about 2 DU/decade by using Linear Regression Analysis (LRA) of the monthly averaged TOC levels. The LRA presents the best statistically significant percentage level (p) of greater than 99%. From the comparison of present result with the observations reported over mid, high and polar latitude sites, long-term TOC variability from tropical site is found to be the lowest, followed by their intermediate range from 10 to 30 DU/ decade over mid latitude sites and the highest range from 30 to 50 DU/decade over high to polar latitude. In order to establish the possible linking of reduction in TOC level per decade with other stratospheric dynamic parameters and atmospheric UV aerosols parameter, inter-annual change in average monthly TOC level has shown a strong correlation coefficient (r) of the order of 0.73 (p > 99.9990) with the stratospheric temperature, followed by its observed lower r value of 0.25 (p = 99%) for stratospheric zonal wind and then a significant correlation (r = 0.17; p = 95%) for AI 300 nm (Aerosols Index 300 nm) parameter. The variation of monthly mean meridional wind component does not illustrate a statistically significant correlation (r = 0.13; p < 80%) with their respective multi-year change in mean monthly TOC values. The consequence of such reduction of TOC per decade may be identified as the result of expected enhancement in incident ground UV-radiation level. At the same time, the harmful influence of increasing the UV level seems to be counteracted and reduced with the evidence of observed higher level of AI at 300 nm as high as 3 in the summer months over selected tropical environmental site.

Based on the AIRS satellite spectrometer data (the Aqua platform), the peculiarities are studied of the field of total ozone (TO) under prolonged blocking conditions over the European part of Russia in summer 2010. It is revealed that the spatial distribution of TO values during the period of blocking was characterized by negative TO anomalies (up to -37 DU on the first ten days of August) over the western and northern peripheries of the blocking anticyclone and by positive TO anomalies (up to 60 DU) over the troughs adj oinmg the anticyclone. Possible mechanisms of the formation of TO anomalies are discussed. The results are presented of the validation of TO measurements with the AIRS spectrometer in May-September 2010 obtained from the data of TO measurements with Brewer spectrophotometers at Kislovodsk and Obninsk stations of the global ozone network.

Ozone source–receptor relationships over East Asia have been quantitatively investigated using a chemical transport model including an on-line tracer-tagged procedure, with a particular focus on the source regions of different daily ozone mixing ratios. Comparison with observations showed that the model reproduced surface ozone and tropospheric nitrogen dioxide column densities. Long-range transport from outside East Asia contributed the greatest fraction to annual surface ozone over remote regions, the Korean peninsula, and Japan, reaching 50%–80% of total ozone. Self-contributions accounted for 5%–20% ozone in the Korean peninsula and Japan, whereas the contribution of trans-boundary transport from photochemical production in China was less than 5%–10%. At extra-high ozone levels, self-contributions reached 50%–60% in the Korean peninsula. Ozone source–receptor relationships showed high seasonal variability over East Asia. Significant transport was also found between sub-regions in China, which presents a great challenge to policy-makers because most current control strategies are confined to specific regions.

The influence of stratospheric processes on the troposphere is defined by a multifactorial mechanism containing various geophysical and photochemical processes. This interaction determines the weather and climate of a particular region of the Earth. The number of sudden stratospheric warmings (SSW) over Eurasia has doubled over the past 20 years if compared with the second half of the 20th century. As a result, one had an increase in dangerous weather phenomena associated with those stratospheric-tropospheric interactions. In this regard, there is a certain need for an early forecast of such dangerous weather phenomena and their study within the framework of the climate of a given region. The paper presents a possible mechanism of the interaction of the mesosphere, stratosphere and troposphere layers (the so-called “ozone mechanism”). Due to its orographical and geographical position, the northern region of the East European Plain is characterized by accumulation of total ozone (TO) over this territory and formation of sharp and severe colds during SSW. The conclusion is made about the key contribution of the “ozone mechanism” to the development of SSW in 2018, which has become the largest in the Northern Hemisphere over the past 20 years.

Climatological ozone profile data are widely used as a-priori information for total ozone using DOAS type retrievals as well as for ozone profile retrieval using optimal estimation, for data assimilation or evaluation of 3-D chemistry-transport models and a lot of other applications in atmospheric sciences and remote sensing. For most applications it is important that the climatology represents not only long term mean values but also the links between ozone and dynamic input parameters. These dynamic input parameters should be easily accessible from auxiliary datasets or easily measureable, and obviously should have a high correlation with ozone. For ozone profile these parameters are mainly total ozone column and temperature profile data. This was the outcome of a user consultation carried out in the framework of developing a new, dynamic ozone profile climatology. The new ozone profile climatology is based on the Neural Network Ozone Retrieval System (NNORSY) widely used for ozone profile retrieval from UV and IR satellite sounder data. NNORSY allows implicit modelling of any non-linear correspondence between input parameters (predictors) and ozone profile target vector. This paper presents the approach, setup and validation of a new family of ozone profile climatologies with static as well as dynamic input parameters (total ozone and temperature profile). The neural network training relies on ozone profile measurement data of well known quality provided by ground based (ozonesondes) and satellite based (SAGE II, HALOE, and POAM-III) measurements over the years 1995–2007. In total, four different combinations (modes) for input parameters (date, geolocation, total ozone column and temperature profile) are available. The geophysical validation spans from pole to pole using independent ozonesonde, lidar and satellite data (ACE-FTS, AURA-MLS) for individual and time series comparisons as well as for analysing the vertical and meridian structure of different modes of the NNORSY ozone profile climatology. The NNORSY ozone profile climatology is available to the community as a comprehensive software library.

This paper describes the comparison of the variability of total column ozone inferred from the three independent multi-year data records, namely, (i) Solar Backscatter Ultraviolet Instrument (SBUV) v8.6 profile total ozone, (ii) GTO (GOME-type total ozone), and (iii) ground-based total ozone data records covering the 16-year overlap period (March 1996 through June 2011). Analyses are conducted based on area-weighted zonal means for 0–30° S, 0–30° N, 50–30° S, and 30–60° N. It has been found that, on average, the differences in monthly zonal mean total ozone vary between −0.3 and 0.8 % and are well within 1%. For GTO minus SBUV, the standard deviations and ranges (maximum minus minimum) of the differences regarding monthly zonal mean total ozone vary between 0.6–0.7% and 2.8–3.8% respectively, depending on the latitude band. The corresponding standard deviations and ranges regarding the differences in monthly zonal mean anomalies show values between 0.4–0.6% and 2.2–3.5%. The standard deviations and ranges of the differences ground-based minus SBUV regarding both monthly zonal means and anomalies are larger by a factor of 1.4–2.9 in comparison to GTO minus SBUV. The ground-based zonal means demonstrate larger scattering of monthly data compared to satellite-based records. The differences in the scattering are significantly reduced if seasonal zonal averages are analyzed. The trends of the differences GTO minus SBUV and ground-based minus SBUV are found to vary between −0.04 and 0.1% yr−1 (−0.1 and 0.3 DU yr−1). These negligibly small trends have provided strong evidence that there are no significant time-dependent differences among these multi-year total ozone data records. Analyses of the annual deviations from pre-1980 level indicate that, for the 15-year period of 1996 to 2010, all three data records show a gradual increase at 30–60° N from −5% in 1996 to −2% in 2010. In contrast, at 50–30° S and 30° S–30° N there has been a levelling off in the 15 years after 1996. The deviations inferred from GTO and SBUV show agreement within 1%, but a slight increase has been found in the differences during the period 1996–2010.

Thirty years of total ozone column (TOC) measurements conducted by a Brewer spectrophotometer, operating in Thessaloniki (40.6°) since March 1982, have been analyzed using the statistical extreme value theory for the identification of extreme TOC events. About 12 % of the total number of days with TOC measurements were identified as extreme-low and ∼15 % as extreme-high events. The influence of the extreme-low events on the annual mean TOC values is up to ∼18 DU, while the extreme-high events show lower impact (up to 12 DU). Removing the extreme events from the time series results in smoother year-to-year variability and reduction of the small long-term linear trend (−0.08 %/year) by a factor of 2. Furthermore, we examined the impact of the extreme events on the noon erythemal irradiance under clear skies, and we provide evidence that even under extreme-low TOC conditions, the UV radiation levels are determined to a great extent by the aerosol optical depth. Although the influence of aerosols is evident during all seasons, for spring and summer, the sensitivity of UV radiation is larger, probably due to the different nature of the aerosols over Thessaloniki during these seasons.

In this study, we investigated the susceptibility of the Dobson spectrophotometer No. 118 to stray light interference. In this regard, a series of total ozone content measurements were carried out in Athens, Greece for air-mass values (μ) extending up to μ = 5. The monochromatic-heterochromatic stray light derived by Basher's model was used in order to evaluate the specific instrumental parameters which determine if this instrument suffers from this problem or not. The results obtained indicate that the measurements made by the Dobson instrument of the Athens station for air mass values up to 2.5, underestimates the total ozone content by 3.5 DU in average, or about 1 % of the station's mean total ozone content (TOC). The comparison of the values of the same parameters measured 15 years ago with the present ones indicates the good maintenance of the Dobson spectrophotometer No. 118. This fact is of crucial importance because the variability of the daily total ozone observations collected by the Athens Dobson Station since 1989 has proved to be representative to the variability of the mean total ozone observed over the whole mid-latitude zone of the Northern Hemisphere. This stresses the point that the Athens total ozone station, being the unique Dobson station in south-eastern Europe, may be assumed as a ground truth station for the reliable conversion of the satellite radiance observations to total ozone measurements.

According to the results of ground-based spectrometric measurements, significant negative anomalies in the stratospheric content of NO2 were observed at a number of stations in the Northern Hemisphere during winter and spring 2011. These anomalies were accompanied by those in total ozone content (TOC) and stratospheric temperature and were caused by the transport of air masses from the region of the arctic ozone hole. The results of analysis of vertical NO2 profiles obtained at the Zvenigorod Scientific Station showed that a certain contribution to the 2011 negative anomalies of NO2 was made due to a denitrification of the polar stratosphere in the ozone-hole region. The relation between variations in the total content of NO2 and those in the TOC and temperature was analyzed for both the Northern and Southern hemispheres during winter–spring periods. It was found that this relation depends on the phase of the quasi-biennial oscillation in the stratospheric equatorial wind. Such a correlation usually intensifies if only the episodes of negative anomalies caused by the transport of stratospheric air masses from the ozone-hole region are taken into consideration.

The characteristics of spatiotemporal distribution of total ozone have a significant impact on the variabilities of climate and environment. As the increase of the high quality and quantity of total ozone datasets, it is necessary to provide a detailed investigation of spatiotemporal distribution characteristics of total ozone and its relationship with climate variability. Based on the ECMWF global monthly mean total ozone and stratopheric temperature data from 1979 to 2013, the spatiotemporal structure of dominant total ozone pattern in the Northern Hemisphere (north of 20°N) during boreal winter is studied using the rotated empirical orthogonal function (REOF) analysis and Morlet wavelet analysis. Besides, the relationship of the dominant total ozone pattern with the temperature anomalies in the upper (2 hPa), middle (30 hPa) and lower (100 hPa) stratosphere is further studied using composite analysis. The results show that the variability of total ozone in the Northern Hemisphere during boreal winter is characterized by five significant dominant patterns during the recent 30 years, which are located in the Arctic region (75°N–90°N, 0°–360°), the subtropics of Northern Hemisphere (20°N–40°N, 0°–360°), the Alaska region (60°N–75°N, 180°E–260°E), the North Atlantic region (45°N–60°N, 310°E–360°E) and the Siberia region (50°N–65°N, 80°E–130°E). The five dominant patterns show significant variabilities on the interannual and interdecadal time scales. The total ozone over these five regions changes from more than normal to less than normal since the late 1980. On the interannual time scale, total ozone over the five regions shows pronounced periodicity. In addition, their periodicities show significant difference. The relationship between the dominant total ozone patterns and the stratospheric temperature indicates that, when the total ozone is increased (reduced), the upper stratosphere will be cooled (warmed), while the middle and lower stratosphere will be warmed (cooled). Furthermore, the middle stratosphere is warmer (cooler) than the lower stratosphere.

Wang, W.; Chai, S.; Wang, H.; Fan, W.; Yu, K.; Liang, S., and Ma, J., 2015. The influence of sulfur dioxide on dobson spectrophotometer total ozone measurement: Analysis on the basis of theoretical factor. Using the WOUDC observational data and absorption cross sections of O3 and SO2, SO2, the paper has calculated absorption coefficients and the theoretical factor C to analyze the influence of sulfur dioxide (SO2) on Dobson spectrophotometer total ozone measurement. The calculation results show that: SO2 absorption coefficient ΔγAD is 1.843, and influence factor C related to ΔγAD has obvious seasonal variation that reaches a maximum in winter and a minimum in summer; moreover, the presence of SO2 leads to higher amount of Dobson ozone than the actual values. After the correction by using the factor C, the relative difference between Dobson and Brewer data sets shows a decrease by 1∼3%. On the other hand, the effect of SO2 on Dobson total ozone is reduced due to the decrease of total SO2, but it s...

Total ozone column TOC obtained from the Ozone Monitoring Instrument OMI on board the Aura satellite was utilized to examine the spatio-temporal distribution of atmospheric ozone over Pakistan and adjoining regions of Afghanistan, India, and Iran for October 2004 to March 2014. This region has not yet been evaluated in greater detail. A yearly spatial averaged value of 278 ± 2 DU was found over the region. A decadal increase of 1.3% in TOC value over study region was observed for the first time. Large spatial and temporal variability of TOC was found over the study region. Elevated ozone columns were observed over the regions with high NO2 and CO concentrations. Analysis indicated that Srinagar city has the highest averaged value of 290 ± 3 DU whereas Jodhpur city showed the highest increasing trend of 1.9% per decade. A monthly averaged maximum value of 289 ± 8 DU and a minimum of 264 ± 5 DU were found during April and November, respectively, over the region. January showed a decreasing trend of −0.8% and February exhibited the highest increasing trend of 5.1% per decade. Forward trajectory analysis showed the possibility of ozone transport from eastern parts of the study region towards the Indian Ocean Bay of Bengal through the subtropical jet stream creating low values at higher meridians in October. TOC data deduced from OMI and the Atmospheric Infrared Sounder were compared to check the level of correlation and the results showed significant correlation r = 0.75 and an acceptable average relative difference of 4.2%.

The variability of ozone over Egypt has been studied in this work. Higher values of coefficient of variation (COV) at eight stations occur at winter while lowest values occur at summer. The COV is function of latitude in annual, winter and spring where it decreases gradually from the north to south of Egypt. The trend analysis of ozone over the eight stations indicates negative trends over northern stations for both annual and seasonal time series with the greatest one at winter. The horizontal distribution of ozone trend values is negative over all Egypt in winter while it positive over middle and south Egypt in the other seasons. The long-term variability of the behavior of the annual ozone shows positive trend values in ozone are the dominant features during the period 1979- 1989 at the most stations. Negative trend values in ozone are the dominant features during the period 1990- 2014 at all stations. The Mann–Kendall test confirms that there is an abrupt change towards decreasing of ozone occurs in 1981, 1984, 2012, 1999, 2000, 1998 and 2010, while a change towards increasing of ozone appears in 2006, 2014, 1993 and 1989.

The solar backscattered ultraviolet (SBUV/SBUV-2) merged ozone datasets, version 8.6, including column ozone and ozone profiles for the 1979–2012 period are examined for the 35°N–60°N zonal belt in the northern hemisphere mid-latitudes and four sub-regions: central Europe, continental Europe, North America, and East Asia. The residual long-term patterns for total ozone and ozone profiles are extracted by smoothing the time series of differences between the original and the modelled ozone time series. Modelled ozone is obtained using the standard trend model accounting for ozone variability due to changes in stratospheric halogens and various dynamical factors commonly used in previous ozone trend analyses. Since about 2005 spring and summer total ozone in the troposphere and lower stratosphere has decreased in some regions (central and continental Europe, North America, and the 35°N–60°N zonal belt) compared with modelled ozone. The negative departure from modelled ozone in 2010 is approximately 2...

We have investigated the impact of the assumed nitrous oxide (N2O) increases on stratospheric chemistry and dynamics using a series of idealized simulations with a coupled chemistry-climate model (CCM). In a future cooler stratosphere the net yield of NOy from N2O is shown to decrease in a reference run following the IPCC A1B scenario, but NOy can still be significantly increased by extra increases of N2O over 2001–2050. Over the last decade of simulations, 50% increases in N2O result in a maximal 6% reduction in ozone mixing ratios in the middle stratosphere at around 10 hPa and an average 2% decrease in the total ozone column (TCO) compared with the control run. This enhanced destruction could cause an ozone decline in the first half of this century in the middle stratosphere around 10 hPa, while global TCO still shows an increase at the same time. The results from a multiple linear regression analysis and sensitivity simulations with different forcings show that the chemical effect of N2O increases dominates the N2O-induced ozone depletion in the stratosphere, while the dynamical and radiative effects of N2O increases are overall insignificant. The analysis of the results reveals that the ozone depleting potential of N2O varies with the time period and is influenced by the environmental conditions. For example, carbon dioxide (CO2) increases can strongly offset the ozone depletion effect of N2O.

At Uccle, Belgium, a long time series (1991–2013) of simultaneous measurements of erythemal ultraviolet (UV) dose (Sery), global solar radiation (Sg), total ozone column (Q_{O3}$) and aerosol optical depth (τaer) (at 320.1 nm) is available, which allows for an extensive study of the changes in the variables over time. Linear trends were determined for the different monthly anomalies time series. Sery, Sg and QO3 all increase by respectively 7, 4 and 3% per decade. τaer shows an insignificant negative trend of −8% per decade. These trends agree with results found in the literature for sites with comparable latitudes. A change-point analysis, which determines whether there is a significant change in the mean of the time series, is applied to the monthly anomalies time series of the variables. Only for Sery and QO3, was a significant change point present in the time series around February 1998 and March 1998, respectively. The change point in QO3 corresponds with results found in the literature, where the change in ozone levels around 1997 is attributed to the recovery of ozone. A multiple linear regression (MLR) analysis is applied to the data in order to study the influence of Sg, QO3 and τaer on Sery. Together these parameters are able to explain 94% of the variation in Sery. Most of the variation (56%) in Sery is explained by Sg. The regression model performs well, with a slight tendency to underestimate the measured Sery values and with a mean absolute bias error (MABE) of 18%. However, in winter, negative Sery are modeled. Applying the MLR to the individual seasons solves this issue. The seasonal models have an adjusted R2 value higher than 0.8 and the correlation between modeled and measured Sery values is higher than 0.9 for each season. The summer model gives the best performance, with an absolute mean error of only 6%. However, the seasonal regression models do not always represent reality, where an increase in Sery is accompanied with an increase in QO3 and a decrease in τaer. In all seasonal models, Sg is the factor that contributes the most to the variation in Sery, so there is no doubt about the necessity to include this factor in the regression models. The individual contribution of τaer to Sery is very low, and for this reason it seems unnecessary to include τaer in the MLR analysis. Including QO3, however, is justified to increase the adjusted R2 and to decrease the MABE of the model.

This study compares, for the first time, the total ozone columns derived from the Ozone Monitoring Instrument-Differential Optical Absorption Spectroscopy (OMI-DOAS algorithm) (TOCs-OMI) with those obtained from ground-based Brewer and Dobson spectrophotometers (TOCs-Ground) in Seoul, a megacity in northeast Asia, over the 3 years between 2008 and 2010. We found a seasonal mean underestimation of 2.68% (maximum 18.33% on a single day) in TOCs-OMI when compared with TOCs-Ground from Seoul, particularly during the summer seasons (June, July, and August) of our study period: 20 of the 30 days when this underestimation of TOCs-OMI was greatest occurred during the summer. The causes of such large underestimations in summer TOCs-OMI were investigated, and we found that the ghost column densities (GCDs) used in the current OMI-DOAS algorithm did not fully account for the tropospheric ozone amounts below the cloud top in Seoul, particularly during the summer season when surface ozone is enhanced due to active photochemical reactions. We propose the use of New TOCs-OMI based on New GCDs that were calculated using ozonesonde data for the limited number of days when such data were available. The mean bias errors (MBE) against the TOCs-Ground of the New TOCs-OMI and original TOCs-OMI were −0.60% and −2.16%, respectively, which demonstrates the greater accuracy of the New TOCs-OMI. To increase the amount of New TOCs-OMI data available for comparison with the TOCs-Ground data, the regression equation for the relationship between the ozonesonde data and OMI-DOAS cloud pressure data was used to increase the availability of New GCD data for each measurement date that TOCs-OMI data were available for. This procedure reduced the MBE of the original TOCs-OMI by 1.29%, 1.67%, and 1.29% in June, July, and August, respectively. The present study demonstrates that the underestimation of GCDs is one of the major causes of the underestimation of TOCs-OMI during the summer season and suggests that improvements could be achieved using the proposed correction for these GCDs.

Statistical models that account for the separate influences on total atmospheric ozone of ozone-depleting substances, anthropogenic greenhouse gases, and natural processes are formulated from the Merged Ozone Data (MOD V8 and V8.6) and used to explore scenarios for ozone’s evolution from 1900 to 2100. The statistical models based on MOD V8 project larger growth in total ozone during the twenty-first century than do coupled chemistry–climate models globally and in the tropics where the chemistry–climate models indicate persistent ozone depletion. The statistical models based on MOD V8.6 suggest, instead, that total ozone everywhere never (or barely) recovers to 1980 levels. Since the decline in ozone-depleting substances and the increase in greenhouse gas concentrations are both expected to increase ozone in the twenty-first century, these results suggest that downward instrumental drifts may be present in MOD V8.6. Instrumental drifts, of opposite sign, may also be present in MOD V8 since it is possible to reduce the projections of the corresponding statistical models to agree with those of the chemistry–climate models by altering the long-term trends of the MOD V8 data within the estimated long-term uncertainty. Alternatively, the chemistry–climate models may project excess tropical ozone depletion by overestimating trends in the upwelling of tropical (ozone poor) air associated with global warming and the resultant decline in mean age of air. This possibility is consistent with independent observations that the age of stratospheric air has not declined during the past three decades, as the globe has warmed 0.3°C, and that model parameterizations of tropical convection may be inadequate.

This study presents an analysis of a 14-year data set of 30-min averaged experimental UVI values derived from ground-based broadband irradiance measurements, satellite-derived total ozone observations and total solar radiation recorded in Barcelona (NE Spain). Most maximum daily UVI values do occur at noon (82% of cases between 11:30 and 13:00 UTC). Considering all seasons, the maximum daily UVI presents a bimodal, approximately symmetrical, frequency distribution with a maximum around UVI class 2 (22%) and UVI 7 and 8 classes (23%) while June median presents a value of 8.2. According to attenuation criteria there is a preponderance of Clear sky days (77%) compared to Broken (22%) and Overcast (8%) conditions, which concentrate mostly in October, November and December (reaching 20% of days). An additional classification in terms of World Health Organisation UVI intensity categories indicates that 40% of days exceeded the Lower threshold of UVI category Moderate (UVI values above 5.5), from them 21% of days had UVI values considered Very High (above 9.5) and one single case was classified as Extreme (UVI above 10.5). UVI values above 7.5 were found under Broken sky conditions in June, July and August. Additionally UVI diurnal daily cycles have also been analyzed in terms of selected percentile values and maximum levels. Under all sky conditions UVI median values exceed the lower threshold of category High (5.5) from April to late August around noon (in June from 10:00 to 14:30 UTC). These results provide an exhaustive quantitative description of average and extreme values of experimental UVI values observed in the region and can be of interest for a wide range of applications, including ground-based UV modelling through the use of radiative transfer models, trend analysis or verification of UVI forecasts.

This paper proposes a method to calculate the ozone radiative forcing (RF) at surface in the ultraviolet (UV) spectral range for all-sky conditions based on the estimation of the ozone efficiency (OE) from experimental data that are subsequently applied to changes on the total ozone column (TOC) since late 1970s. The OE is defined as the rate at which the solar UV irradiance is “forced” per TOC unit, being estimated for all-sky conditions from UV-B (280–320 nm) and TOC data recorded with a Bentham spectroradiometer at Granada (Spain). The results showed a clear seasonal pattern in the OE values with largest monthly averages (in absolute terms) in July (−4.2 ± 0.3 mW/m2 per Dobson Unit) and the smallest in January (−0.7 ± 0.3 mW/m2 per Dobson Unit). The continuous and consistent TOC data set (1979–2008) provided by the Multisensor Reanalysis over the study site showed that spring months present the largest annual TOC changes relative to 1979 while summer months exhibit small variations. Thus, spring has the largest contribution (~53%) to annual ozone RF followed by summer (~17%), winter (~16%), and autumn (~4%). The evolution of the ozone RF relative to 1979 in the UV-B range at Granada showed positive values for most of years (between 5 and 40 mW/m2). Finally, the long-term evolution of the ozone RF exhibited a positive trend until the mid-1990s and, subsequently, a weak negative trend until the end of the analyzed period.

Ozone (O3) reduction caused by dust particles is a challenging topic that has not been sufficiently investigated. Previous studies have provided limited quantification of O3, mainly based on case studies or short-term campaigns. In this paper, 157 O3 vertical profiles from ozone soundings launched from the Canary Islands over 13 summers are analyzed. Using aerosol optical depth as a discrimination tool, the data are classified into two groups: clean atmospheric conditions and dusty conditions under the presence of the Saharan Air Layer (SAL). The results show that ozone mixing ratios on SAL days are systematically lower than those during clean conditions, with a difference of as much as 35%. An analysis of independent total ozone columns from ground-based and satellite spectrometers confirm the observed O3 reductions. In addition, a vertical redistribution of the total water content takes place during these events. A comparison of the vertical shape of the O3 reductions with the vertical distribution of dust loading and precipitable water vapor shows that although O3 reductions occur in parts of the layer where the dust is present, a better correlation is found with the total amount of water present in the air. This finding suggests that the latter component plays a role in the observed O3 reduction within the SAL.

Umkehr and total ozone measurements have been carried out at Hoher Sonnblick (47.05°N, 12.95°E; 3106 m above sea level) since 1994 with the Brewer MkIV #093 spectrophotometer. These measurements are used to investigate trends in total and vertically resolved ozone in the period 1994–2011 and for establishing an Umkehr climatology. A method to estimate daily thresholds for extreme events in total ozone (TO3) based on skewed log-Weibull distributions is presented and applied to the record. An analysis of the such defined extreme events reveals a significant decline in the number of low events, whereas the high events increased by about the same amount. However, no significant trend is observed in the magnitude of extreme events. Solar activity and equivalent effective stratospheric chlorine show weak to no correlation with vertically resolved ozone, presumably due to the record's limited extent, while tropopause pressure and quasi-biennial oscillation show a significant influence. Trend analysis of total and vertically resolved ozone indicates a significant increase in TO3 of 2.0% per decade since 1994, whereas no recovery is observed in the upper stratosphere. While ozone concentrations continue to decrease or stagnate in the upper stratosphere, the loss is overcompensated by large gains in the lowest layers during winter, leading to a significant overall increase in TO3. During events with extremely low TO3, the largest deficiencies are found in the bottommost layers with a marked seasonal component. The topmost layers mainly contribute to TO3 reductions during late winter and fall.

The Australian Bureau of Meteorology maintains a number of long-running Dobson measurement programs, among the few in southern hemisphere mid-latitudes. Data from the Melbourne site (the Melbourne/Airport World Ozone and Ultraviolet Radiation Data Centre (WOUDC) station was originally located at Aspendale, then moved to the city centre, and finally to Melbourne Airport) from 1978 to 2012 have recently been reviewed and re-evaluated. These data are analyzed using multi-linear regression and also by application of an 11-year running mean. Satellite data from the Merged Ozone Dataset are also used for comparison with the Dobson results. We show that the Quasi-Biennial Oscillation (QBO) plays a major role in winter and spring once phase is taken into account by month. We also show that the three so-called “classical” proxies (QBO, solar cycle, and Equivalent Effective Stratospheric Chlorine (EESC)) alone are able to give a good fit to ozone for Melbourne and, more generally, the southern mid-latitudes...

[1] We conducted a first-order sensitivity analysis to investigate ozone responses to precursor emissions and source contributions (local versus upwind) for California's San Joaquin Valley (SJV) under four distinct meteorology conditions of summer 2000 using a three-dimensional photochemical transport model. Ozone-limiting reagents, nitrogen oxides (NOx), or anthropogenic volatile organic compounds (VOCs) (AVOCs) and their transition regime were determined from ozone sensitivity coefficients and delineated spatially at high-ozone locations in the SJV. In general, AVOC-limited areas were located near urban centers, while NOx-limited areas were located farther downwind. However, the spatial extent of AVOC-limited areas varied with meteorology. Meteorological dependence of predominant ozone-limiting precursors was found to vary significantly among different subregions within the SJV. Specifically, weaker dependences were identified for regions of the southern SJV located farther away from emission sources, where ozone chemistry was mostly limited by NOx for the episodes considered. Stronger dependences were identified for the central and northern SJV, where ozone chemistry can be limited by NOx or AVOC depending on meteorology. Source contributions to ozone sensitivities in the SJV were also investigated. Local sources were important for the eastern side of the central SJV, while upwind sources were also important (from ~40% to more than 50% of the total ozone sensitivities) for the western side of the valley, except for the most stagnant episode. Different contributing source regions were identified for the same VOC-limited areas in the northern SJV, and these depended on the flow characteristics. The predominant ozone-limiting reagent was found to exhibit less dependence on meteorology in the central and southern SJV as the baseline NOx emissions were reduced, ultimately causing ozone formation to be limited by NOx. In contrast, the VOC-limited areas in the northern SJV continued to be influenced by meteorology for two of the episodes.

[1] Three Brewer spectrophotometers were set up in three tropical sites of South America (in the Bolivian Altiplano and seashore and biomass burning areas of Brazil) to measure the total ozone column (TOC). Only TOC measurements with uncertainties ≤1% (1σ) were considered. Typically, the standard deviation for the diurnal sets of measurements was predominantly ≤1% for two of these sites. The average variability in TOC ranged from 6.3 Dobson units (DU) to 16.8 DU, and the largest variability reached 54.3 DU. Comparisons between ground-based and satellite (Total Ozone Mapping Spectrometer (TOMS)) data showed good agreement with coefficients of determination ≤0.83. However, the quality of the ground-based measurements was affected by the weather condition, especially for one of the sites. Visual observation of the sky from the ground during the measurements with one of the Brewers added to the satellite data of reflectivity and aerosol index supports that statement.

This paper focuses on the long-term declining change in total ozone column TOC derived from satellite measurements over a 25 year period over two neighbouring tropical Asian sites, Karachi, and Mt Abu. A strong declining trend was observed in TOC at both sites, with a significance level of over 95% and a higher magnitude of 4 to 10 DU per decade in September to December and a weak statistical significance level of below 85% and a lower magnitude of 2 to 4 DU per decade in pre-monsoon months. However, during the monsoon months, a small declining trend of about 1 DU per decade was observed, but this variation is statistically insignificant. Further, the long-term changes in TOC exhibit seasonal dependence with a more negative change of 10 DU per decade in winter over Karachi and 7 DU per decade over Mt Abu. The consequence of such a net long-term declining change in TOC as high as 10 DU per decade is expected to have serious environmental implications due to an overall increase in ground-level solar UV radiation of 18% over the normal values in the tropics. In order to identify some plausible causes of this depletion trend in ozone concentration with stratospheric temperature and solar activity, it is clear that there is a strong relationship between the seasonal dependence of the long-term declining trend of TOC on air temperature at 10 mb or stratospheric cooling. At the same time, there is a less significant long-term variation in TOC due to altered solar activity levels.

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.

A Tibetan ozone low was found in the 1990s after the Antarctic ozone hole. Whether this ozone low has been recovering from the beginning of the 2000s following the global ozone recovery is an intriguing topic. With the most recent merged TOMS/SBUV (Total Ozone Mapping Spectrometer/Solar Backscatter Ultra Violet) ozone data, the Tibetan ozone low and its long-term variation during 1979–2010 are analyzed using a statistical regression model that includes the seasonal cycle, solar cycle, quasi-biennial oscillation (QBO), ENSO signal, and trends. The results show that the Tibetan ozone low maintains and may become more severe on average during 1979–2010, compared with its mean state in the periods before 2000, possibly caused by the stronger downward trend of total ozone concentration over the Tibet. Compared with the ozone variation over the non-Tibetan region along the same latitudes, the Tibetan ozone has a larger downward trend during 1979–2010, with a maximum value of −0.40±0.10 DU yr−1 in January, which suggests the strengthening of the Tibetan ozone low in contrast to the recovery of global ozone. Regression analyses show that the QBO signal plays an important role in determining the total ozone variation over the Tibet. In addition, the long-term ozone variation over the Tibetan region is largely affected by the thermal-dynamical proxies such as the lower stratospheric temperature, with its contribution reaching around 10% of the total ozone change, which is greatly different from that over the non-Tibetan region.

Mean global total ozone is estimated as the latitudinally weighted average of total ozone measured by the TOMS and OMI satellite mounted ozone measurement devices for the periods 1979-1992 and 2005-2015 respectively. The TOMS dataset shows an OLS depletion rate of 0.65 DU per year on average in mean monthly ozone from January 1979 to December 1992. The OMI dataset shows an OLS accretion rate of 0.5 DU per year on average in mean monthly ozone from January 2005 to December 2015. The conflicting and inconsequential OLS trends may be explained in terms of the random variability of nature and violations of OLS assumptions that can create the so called Hurst phenomenon. These findings are inconsistent with the Rowland-Molina theory of ozone destruction by anthropogenic chemical agents because the theory implies continued and dangerous depletion of total ozone on a global scale until the year 2040.

Latitudinally weighted monthly mean global ozone is estimated using total ozone data from sixteen ground stations at latitudes from 89 S to 71 N and longitudes 170 E to 170 W. Data from all sixteen stations are available without gaps for a 29-year sample period from January 1987 to December 2015. The monthly mean global ozone series does not show a sustained decline that can be interpreted in terms of the Rowland-Molina-UNEP theory of ozone destruction by man-made halogenated hydrocarbons. The findings validate the results of a prior work which used satellite data for trends in mean global total ozone over much shorter sample periods.

Annual Cyclic Variations (ACV) in the Total Ozone Column (TOC) were estimated in latitudinally averaged Multi Sensor Reanalysis (MSR) monthly mean TOC time-series data-set from Jan 1979 to Dec 2008 for Indian region. The TOC contents over any latitude is controlled by the photochemistry and dynamics present in different regions of the stratosphere and troposphere, correlation between ACV in TOC, and ACV in other climatic and dynamical factors—(i) Solar Insolation on a horizontal surface at the top of the atmosphere (ETSI); (ii) Zonal Wind at 30 hPa pressure level (ZW); (iii) Meridional Wind at 30 hPa pressure level (MW); and (iv) Air Temperature at 30 hPa pressure level (AT)—were taken into account to understand their role in the annual cyclic variability present in the TOC over Indian region. Contributions of ACV present in these climatic and dynamical factors to the ACV in TOC were ascertained by performing a multiple linear regression analysis by taking ACV in ETSI, ACV in ZW and ACV in AT as independent variables (co-variates) for ACV in TOC. It is concluded that in the tropical part of Indian region ACV in TOC is largely controlled by the photochemistry; whereas in the subtropical part of the region, the dynamics present in the stratosphere mainly decides ACV in TOC.