Satellite Ozone Research Articles

Ozone layer state and level of ultraviolet irradiance over the territory of Ukraine in 2019

The paper presents main results of total ozone column (TOC) and levels of ultraviolet irradiance daily monitoring conducted for the Ukrainian territory in 2019. Monitoring and analysis were performed using TOC data measured by the satellite Ozone Monitoring Instrument (the OMI) and estimated values of ultraviolet index. The research was made on the regular grid with 1° spatial resolution and separately for geographical coordinates of centers of Ukrainian administrative regions. In 2019 the TOC ranged within a multiyear average standard with and its average value was equal to 260–360 D.u. During winter ozone concentration reached its highest values due to intensification of Brewer-Dobson circulation. Weakened polar vortex and ozone-rich air masses advection at the upper atmospheric levels which transport high ozone concentrations, resulted in the TOC positive anomalies emergence over Ukraine. The air masses penetrated Ukrainian territory from the north-west and this led to emergence anomalously high TOC values during a number of periods: February 23–24, March 2, March 12–14, March 26. In these periods 450–500 D.u. was a typical ozone content. Seasonal TOC decrease, observed from April to June, was caused by a weakened Brewer-Dobson circulation and intensification of photochemical ozone loss. Nevertheless, TOC deviations from average standard were negligible and this resulted in absence of very high UV-index values. The highest UV-index values did not reach 7 units. In July the TOC was slightly higher than usual concentrations, which was probably caused by dynamic factors. Such TOC values influenced the level of ultraviolet irradiance and the UV-index varied within 3–4 units' range which is typical for Ukraine in April–May. Such ozone state in 2019 made it impossible for UV-index to reach extremely high levels, especially during the summer period. Further TOC changes were characterized by typical seasonal ozone decrease with minimum values observed in October resulted from formation and intensification of polar vortex. Average minimum values in October amounted to 260–270 D.u., however, it is a typical TOC content for this period with a relative deviation from the standard constituting about -0.3σ. Seasonal ozone increase in 2019 started in mid-November. At the end of December the first high positive deviations happened. The highest of them reached close to anomalous 2–2.4σ values.

Study of SO Pollution in the Middle East Using MERRA‐2, CAMS Data Assimilation Products, and High‐Resolution WRF‐Chem Simulations

AbstractOil recovery, power generation, water desalination, gas flaring, and traffic are the main contributors to SO emissions in the Middle East (ME). Satellite observations suggest that the traditional emission inventories do not account for multiple SO emission sources in the ME. This study aims to evaluate the most frequently used SO emission data sets over the ME by comparing high‐resolution regional model simulations and meteorology/chemistry assimilation products, MERRA‐2 and CAMS, with satellite and available ground‐based air‐quality observations. Here, we employ the WRF‐Chem‐3.7.1 regional meteorology‐chemistry model and conduct simulations for the period 2015–2016 with 10 km grid spacing using HTAP‐2.2 emission data sets and the new OMI‐HTAP data, which is based on the combination of the near‐surface SO emissions taken from the HTAP‐2.2 inventory with strong (>30 kt/year) SO point sources obtained from the satellite Ozone Monitoring Instrument (OMI) observations. We find that conventional emission inventories (EDGAR‐4.2, MACCity, and HTAP‐2.2) have uncertainties in the location and magnitude of SO sources in the ME and significantly underestimate SO emissions in the Arabian Gulf. The WRF‐Chem, run in conjunction with the new OMI‐HTAP emissions, improves comparisons between the satellite and ground‐based SO observations. Our simulations show that SO surface concentrations in Jeddah and Riyadh frequently exceed European air‐quality limits. The ME generates about 10% of global anthropogenic SO emissions, on par with India. Therefore, the development of effective emission controls and improvement of air‐quality monitoring in the ME are urgently needed.

Early results and validation of SAGE III-ISS ozone profile measurements from onboard the International Space Station

Abstract. The Stratospheric Aerosol and Gas Experiment III (SAGE III, 2018) instrument was launched on 19 February 2017 from the NASA Kennedy Space Center and was integrated aboard the International Space Station (ISS). SAGE III-ISS has been providing ozone profile measurements since June 2017. This paper presents an early validation of the Level 2 solar and lunar occultation ozone data products using ground-based lidar and ozonesondes from Hohenpeißenberg and Lauder as well as satellite ozone vertical products from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument. Average differences in the ozone concentration between SAGE III-ISS and Hohenpeißenberg lidar observations for 1 year are less than 10 % between 16 and 42 km and less than 5 % between 20 and 40 km. Hohenpeißenberg ozonesonde comparisons are mostly within 10 % between 18 and 30 km. The Lauder lidar comparison results are less than 10 % between 17 and 37 km, and the Lauder ozonesonde comparison results are less than 10 % between 19 and 31 km. The seasonal average differences in the ozone concentration between SAGE III-ISS and ACE-FTS are mostly less than 5 % between 20 and 45 km for both the Northern Hemisphere and Southern Hemisphere. All results from these comparisons show that the SAGE III-ISS ozone solar data compare well with correlative measurements throughout the stratosphere. With few comparisons available, the percentage difference between the SAGE III-ISS lunar ozone data and the ozonesonde data is less than 10 % between 19 and 27 km. The percentage difference between the SAGE III-ISS lunar ozone data and the ACE-FTS ozone data is less than 10 % between 20 and 40 km.

Toward a Reanalysis of Stratospheric Ozone for Trend Studies: Assimilation of the Aura Microwave Limb Sounder and Ozone Mapping and Profiler Suite Limb Profiler Data

AbstractCompatibility of the stratospheric ozone profile data from the Ozone Mapping and Profiler Suite Limb Profiler (OMPS‐LP) and the Microwave Limb Sounder (MLS) is assessed in the context of a continuity requirement for future reanalyses. A methodology for the assimilation of OMPS‐LP data into the Goddard Earth Observing System data assimilation system with a stratospheric chemistry module is developed. It is demonstrated that a simple homogenization technique significantly reduces the bias between OMPS‐LP and MLS analyses. With the homogenization applied, the mean difference between the two analyses is within 3% and the difference standard deviation within 10%, consistent with the estimated uncertainties of the satellite ozone data. Larger differences are seen in the tropical lower stratosphere. The MLS and OMPS‐LP assimilation experiments agree very well with independent data from ozonesondes and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer. Heterogeneous ozone depletion during polar spring in both hemispheres as well as ozone transport during the 2016 quasi‐biennial oscillation disruption event are realistically represented in both analyses. This work establishes a step toward achieving continuity of the post‐2004 ozone record in future reanalyses, necessary for trend and long‐term ozone variability studies, although further development is needed to address a drift in the OMPS‐LP ozone data.

A study of the influence of tropospheric subsidence on spring and summer surface ozone concentrations at the JRC Ispra station in northern Italy

Abstract. The influence of tropospheric ozone on the surface ozone concentrations is investigated at the monitoring station of JRC Ispra, based on 10 years of measurements (2006–2015) of surface ozone data. In situ hourly measurements of ozone and other air pollutants, meteorological parameters, and weekly averaged 7Be (as an indicator of upper-tropospheric–stratospheric influence) and 210Pb measurements (as an indicator of boundary layer influence) have been used for the analysis. In addition, IASI + GOME-2 and IASI ozone satellite data have also been used. It is observed that frequently 7Be and ozone weekly peaks coincide, which might be explained by the impact of deep atmospheric subsidence on surface ozone, particularly during late spring and early summer. Based on this observation, a detailed analysis of selected 7Be and ozone episodes occurring during that period of the year has been performed in order to further elucidate the mechanisms of tropospheric influence on the surface pollutant concentrations. For the analysis, composite NOAA/ESRL reanalysis synoptic meteorological charts in the troposphere have been used as well as IASI satellite ozone measurements and NOAA HYSPLIT back trajectories. The JRC station hourly measurements during subsidence episodes show very low values of local pollution parameters (e.g., NOx, 222Rn, nephelometer data, PM10), close to zero. Conversely, during these periods ozone levels usually reach values around 45–60 ppb during the afternoon hours but also show significantly higher values than the average during the night and morning hours, which is a sign of direct tropospheric influence on the surface ozone concentrations.

Bias Correction of Multi-sensor Total Column Ozone Satellite Data for 1978–2017

Bias Correction of Multi-sensor Total Column Ozone Satellite Data for 1978–2017

Intercomparison of Ground- and Satellite-Based Total Ozone Data Products at Marambio Base, Antarctic Peninsula Region

This study aims to compare the ground-based Brewer spectrophotometer total ozone column measurements with the Dobson spectrophotometer and various satellite overpass data available at Marambio Base during the period 2011–2013. This station provides a unique opportunity to study ozone variability near the edge of the southern polar vortex; therefore, many institutions, such as the National Meteorological Service of Argentina, the Finnish Meteorological Institute and the Czech Hydrometeorological Institute, have been carrying out various scientific activities there. The intercomparison was performed using total ozone column data sets retrieved from the ground-based instruments and from Ozone Monitoring Instrument (OMI)—Total Ozone Mapping Spectrometer (TOMS), OMI–Differential Optical Absorption Spectroscopy (DOAS), Global Ozone Monitoring Experiment 2 (GOME2), and Scanning Imaging Absorption Spectrophotometer for Atmospheric Cartography (SCIAMACHY) satellite observations. To assess the quality of the selected data products, comparisons with reference to the Brewer spectrophotometer single observations were made. The performance of the satellite observational techniques was assessed against the solar zenith angle and effective temperature, as well as against the actual shape of the vertical ozone profiles, which represent an important input parameter for the satellite ozone retrievals. The ground-based Dobson observations showed the best agreement with the Brewer data set (R2 = 1.00, RMSE = 1.5%); however, significant solar zenith angle (SZA) dependency was found. The satellite overpass data confirmed good agreement with the Brewer observations but were, however, overestimated in all cases except for the OMI(TOMS), when the mean bias differed from −0.7 DU in the case of the OMI(TOMS) to 6.4 DU for the SCIAMACHY. The differences in satellite observational techniques were further evaluated using statistical analyses adapted for depleted and non-depleted conditions over the ozone hole period.

Why Do Antarctic Ozone Recovery Trends Vary?

We use satellite ozone records and Global Modeling Initiative chemistry transport model simulations integrated with Modern Era Retrospective for Research and Analysis 2 meteorology to identify a metric that accurately captures the trend in Antarctic ozone attributable to the decline in ozone depleting substances (ODSs). The GMI CTM Baseline simulation with realistically varying ODS levels closely matches observed interannual to decadal scale variations in Antarctic September ozone over the past four decades. The expected increase or recovery trend is obtained from the differences between the Baseline simulation and one with identical meteorology and fixed 1995 ODS levels. The differences show that vortex-averaged column O3 has the greatest sensitivity to ODS change from 1 to 20 September. The observed vortex-averaged column O3 during this period produces a trend consistent with the expected recovery attributable to ODS decline. Trends from dates after 20 September have smaller sensitivity to ODS decline and are more uncertain due to transport variability. Simulations show that the greatest decrease in O3 loss (i.e., recovery) occurs inside the vortex near the edge. The polar cap metrics have vortex size-dependent bias and do not consistently sample this region. Because the 60-90°S 220 Dobson unit O3 mass deficit metric does not sample the edge region, its trend is lower than the expected trend; this is improved by area weighting. The 250-Dobson unit O3 mass deficit metric samples more of the edge region, which increases its trend. Approximately 25% of the September Antarctic O3 increase is due to higher O3 levels in June prior to winter depletion.

Total Ozone over Vernadsky Antarctic Station: Ground-based and Satellite Measurements

Objective. Provide an analysis of the total ozone variations over Vernadsky Antarctic station (Faraday Base until 1996) from long-term ground-based and satellite series. Study the discrepancies between the data of different instruments. Methods. Data visualization followed by analysis, statistical treatment of the Vernadsky Dobson spectrophotometer observations and satellite total ozone series. Results. Satellite and ground-based measurements of total ozone over Vernadsky station have confirmed the stabilization in the ozone layer in the stratosphere over Antarctica from the early 2000s. British Faraday Base observations have retrieved an ozone spring maximum during the 1950s–1970s with a sharp decrease in the August–October values in the 1980s–1990s. That changed substantially total ozone seasonal cycle. Satellite overpasses and model data based on satellite measurements have been analyzed. It is shown that typical discrepancies between the Ozone Monitoring Instrument (OMI) model and the Vernadsky Dobson daily means are mainly in the range of 20 DU. Larger deviations are rare and are observed predominantly on the beginning and at the end of the observational season. Seasonal means and standard deviations for the model–Dobson differences were calculated that demonstrates worse correspondence of the OMI model with Vernadsky Dobson data during separate years, in particular 2009–2010. Conclusions. Both Dobson and satellite ozone data over Faraday/Vernadsky station have shown the total ozone decrease during the 1980s–1990s (mainly in spring) with a following stabilization since year 2000. Comparison between the ground-based data and models calculated from satellite measurements indicates better correspondence of the Dobson and GOME2 results relatively the OMI ones. There are evidences that individual Dobson measurements underestimate to some degree total ozone on the beginning of observational season at high solar zenith angles and the low total ozone values.

Trends in global tropospheric ozone inferred from a composite record of TOMS/OMI/MLS/OMPS satellite measurements and the MERRA-2 GMI simulation

Abstract. Past studies have suggested that ozone in the troposphere has increased globally throughout much of the 20th century due to increases in anthropogenic emissions and transport. We show, by combining satellite measurements with a chemical transport model, that during the last four decades tropospheric ozone does indeed indicate increases that are global in nature, yet still highly regional. Satellite ozone measurements from Nimbus-7 and Earth Probe Total Ozone Mapping Spectrometer (TOMS) are merged with ozone measurements from the Aura Ozone Monitoring Instrument/Microwave Limb Sounder (OMI/MLS) to determine trends in tropospheric ozone for 1979–2016. Both TOMS (1979–2005) and OMI/MLS (2005–2016) depict large increases in tropospheric ozone from the Near East to India and East Asia and further eastward over the Pacific Ocean. The 38-year merged satellite record shows total net change over this region of about +6 to +7 Dobson units (DU) (i.e., ∼15 %–20 % of average background ozone), with the largest increase (∼4 DU) occurring during the 2005–2016 Aura period. The Global Modeling Initiative (GMI) chemical transport model with time-varying emissions is used to aid in the interpretation of tropospheric ozone trends for 1980–2016. The GMI simulation for the combined record also depicts the greatest increases of +6 to +7 DU over India and East Asia, very similar to the satellite measurements. In regions of significant increases in tropospheric column ozone (TCO) the trends are a factor of 2–2.5 larger for the Aura record when compared to the earlier TOMS record; for India and East Asia the trends in TCO for both GMI and satellite measurements are ∼+3 DU decade−1 or greater during 2005–2016 compared to about +1.2 to +1.4 DU decade−1 for 1979–2005. The GMI simulation and satellite data also reveal a tropospheric ozone increases in ∼+4 to +5 DU for the 38-year record over central Africa and the tropical Atlantic Ocean. Both the GMI simulation and satellite-measured tropospheric ozone during the latter Aura time period show increases of ∼+3 DU decade−1 over the N Atlantic and NE Pacific.

Towards a comprehensive view of dust events from multiple satellite and ground measurements: exemplified by the May 2017 East Asian dust storm

Abstract. One or several aspects of the source, distribution, transport, and optical properties of airborne dust have been characterized using different types of satellite and ground measurements, each with unique advantages. In this study, a dust event that occurred over the East Asia area in May 2017 was exemplified to demonstrate how all the above-mentioned aspects of a dust event can be pictured by combining the advantages of different satellite and ground measurements. The data used included the Himawari-8 satellite Advanced Himawari Imager (AHI) true-colour images, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol vertical profiles, the Aura satellite Ozone Monitoring Instrument (OMI) aerosol index images, and the ground-based Aerosol Robotic Network (AERONET) aerosol properties and the ground station particulate matter (PM) measurements. From the multi-satellite/sensor (AHI, CALIOP, and OMI) time series observations, the dust storm was found to originate from the Gobi Desert on the morning of 3 May 2017 and transport north-eastward to the Bering Sea, eastward to the Korean Peninsula and Japan, and southward to south-central China. The air quality in China deteriorated drastically: the PM10 (PM < 10 µm in aerodynamic diameter) concentrations measured at some air quality stations located in northern China reached 4333 µg m−3. At the AOE_Baotou, Beijing, Xuzhou-CUMT, and Ussuriysk AERONET sites, the maximum aerosol optical depth values reached 2.96, 2.13, 2.87, and 0.65 and the extinction Ångström exponent dropped to 0.023, 0.068, 0.03, and 0.097, respectively. The dust storm also induced unusual aerosol spectral single-scattering albedo and volume size distribution.

Recent Arctic ozone depletion: Is there an impact of climate change?

After the well-reported record loss of Arctic stratospheric ozone of up to 38% in the winter 2010–2011, further large depletion of 27% occurred in the winter 2015–2016. Record low winter polar vortex temperatures, below the threshold for ice polar stratospheric cloud (PSC) formation, persisted for one month in January 2016. This is the first observation of such an event and resulted in unprecedented dehydration/denitrification of the polar vortex. Although chemistry–climate models (CCMs) generally predict further cooling of the lower stratosphere with the increasing atmospheric concentrations of greenhouse gases (GHGs), significant differences are found between model results indicating relatively large uncertainties in the predictions. The link between stratospheric temperature and ozone loss is well understood and the observed relationship is well captured by chemical transport models (CTMs). However, the strong dynamical variability in the Arctic means that large ozone depletion events like those of 2010–2011 and 2015–2016 may still occur until the concentrations of ozone-depleting substances return to their 1960 values. It is thus likely that the stratospheric ozone recovery, currently anticipated for the mid-2030s, might be significantly delayed. Most important in order to predict the future evolution of Arctic ozone and to reduce the uncertainty of the timing for its recovery is to ensure continuation of high-quality ground-based and satellite ozone observations with special focus on monitoring the annual ozone loss during the Arctic winter.

An updated version of a gap-free monthly mean zonal mean ozone database

Abstract. An updated and improved version of a global, vertically resolved, monthly mean zonal mean ozone database has been calculated – hereafter referred to as the BSVertOzone (Bodeker Scientific Vertical Ozone) database. Like its predecessor, it combines measurements from several satellite-based instruments and ozone profile measurements from the global ozonesonde network. Monthly mean zonal mean ozone concentrations in mixing ratio and number density are provided in 5∘ latitude bins, spanning 70 altitude levels (1 to 70 km), or 70 pressure levels that are approximately 1 km apart (878.4 to 0.046 hPa). Different data sets or “tiers” are provided: Tier 0 is based only on the available measurements and therefore does not completely cover the whole globe or the full vertical range uniformly; the Tier 0.5 monthly mean zonal means are calculated as a filled version of the Tier 0 database where missing monthly mean zonal mean values are estimated from correlations against a total column ozone (TCO) database. The Tier 0.5 data set includes the full range of measurement variability and is created as an intermediate step for the calculation of the Tier 1 data where a least squares regression model is used to attribute variability to various known forcing factors for ozone. Regression model fit coefficients are expanded in Fourier series and Legendre polynomials (to account for seasonality and latitudinal structure, respectively). Four different combinations of contributions from selected regression model basis functions result in four different Tier 1 data sets that can be used for comparisons with chemistry–climate model (CCM) simulations that do not exhibit the same unforced variability as reality (unless they are nudged towards reanalyses). Compared to previous versions of the database, this update includes additional satellite data sources and ozonesonde measurements to extend the database period to 2016. Additional improvements over the previous version of the database include the following: (i) adjustments of measurements to account for biases and drifts between different data sources (using a chemistry-transport model, CTM, simulation as a transfer standard), (ii) a more objective way to determine the optimum number of Fourier and Legendre expansions for the basis function fit coefficients, and (iii) the derivation of methodological and measurement uncertainties on each database value are traced through all data modification steps. Comparisons with the ozone database from SWOOSH (Stratospheric Water and OzOne Satellite Homogenized data set) show good agreement in many regions of the globe. Minor differences are caused by different bias adjustment procedures for the two databases. However, compared to SWOOSH, BSVertOzone additionally covers the troposphere. Version 1.0 of BSVertOzone is publicly available at https://doi.org/http://doi.org/10.5281/zenodo.1217184.

Evaluation of the performance of Suomi-NPP OMPS nadir mapper products using station measurements and OMI data

Satellite remote sensing technology provides the only viable means for global monitoring of atmosphere systems, such as ozone. The ozone mapping and profiler suite (OMPS) onboard Suomi-NPP satellite, which was launched in the year 2011, has a primary purpose of measuring ozone. Suomi-NPP has been on operation for more than 3 years, and it is crucial to keep the satellite data precise and trusted. By using 17 months of satellite and ground-based total ozone column (TOC) data, this study performs an evaluation of OMPS products. Ozone monitoring instrument (OMI) data generated from a similar satellite instrument were also used to compare with the OMPS TOC data, and both the TOC products were generated using TOMS version 8.5 (TOMS-V8.5) algorithm. The evaluation consists of intercomparisons with ground-based Brewer measurements, similar satellite instruments, and accuracy analysis as a function of time and solar zenith angle. Results show that after 3 years of operation, OMPS-derived TOC data still have good correlation (R2 > 0.99, RMSE = 1.51 % ) with ground-based measurements. The results also give some evidence that the OMPS TOC data have better accuracy than those from OMI using the same algorithm.

Ozone layer adaptive model from direct relationship between solar activity and total column ozone for the tropical equator-Andes-Colombian region

Due to the lack of models to predict the ozone layer even after an ample range of total column ozone (TCO) measurements around the globe, a direct relationship between solar activity by means of sunspot number observations and total ozone satellite data for a tropical Andes mountains region at Bogota-Colombia, is presented. Sunspot number data and 37 years of TCO records from satellite missions Nimbus 7, Meteor 3, Earth Probe and AURA from January 1979 through August 2016, are analyzed. Ozone annual cyclic behavior, which strongly depends on the annual cyclic Sun-Earth distance variation, as well as the dynamics of the solar activity cycles allow to derive a physical-mathematical adaptive model for predicting and reconstructing daily stratospheric ozone over the city of Bogota, very close to the equator. Results suggest that the ozone layer as a natural indicator of solar activity.

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

ABSTRACTIn 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.

Ozone comparison between Pandora #34, Dobson #061, OMI, and OMPS in Boulder, Colorado, for the period December 2013–December 2016

Abstract. A one-time-calibrated (in December 2013) Pandora spectrometer instrument (Pan #034) has been compared to a periodically calibrated Dobson spectroradiometer (Dobson #061) co-located in Boulder, Colorado, and compared with two satellite instruments over a 3-year period (December 2013–December 2016). The results show good agreement between Pan #034 and Dobson #061 within their statistical uncertainties. Both records are corrected for ozone retrieval sensitivity to stratospheric temperature variability obtained from the Global Modeling Initiative (GMI) and Modern-Era Retrospective analysis for Research and Applications (MERRA-2) model calculations. Pandora #034 and Dobson #061 differ by an average of 2.1 ± 3.2 % when both instruments use their standard ozone absorption cross sections in the retrieval algorithms. The results show a relative drift (0.2 ± 0.08 % yr−1) between Pandora observations against NOAA Dobson in Boulder, CO, over a 3-year period of continuous operation. Pandora drifts relative to the satellite Ozone Monitoring Instrument (OMI) and the Ozone Mapping Profiler Suite (OMPS) are +0.18 ± 0.2 % yr−1 and −0.18 ± 0.2 % yr−1, respectively, where the uncertainties are 2 standard deviations. The drift between Dobson #061 and OMPS for a 5.5-year period (January 2012–June 2017) is −0.07 ± 0.06 % yr−1.

A Comparison of MICROTOPS II and OMI Satellite Ozone Measurements in Novi Sad from 2007 to 2015

In this paper, we present consecutive daily measurements of the total ozone column (TOC) using MICROTOPS II in Novi Sad, the Republic of Serbia (45.3 N, 19.8 E and the altitude of 84 m) from 2007 to 2015. The MICROTOPS II data set was compared to the ozone monitoring instrument (OMI) satellite data, since there was no nearby comparative long-time series available for the Dobson or Brewer instrument. The data quality control of the measured MICROTOPS II TOC data was carried out before the comparison with the satellite data. The MICROTOPS II was calibrated at the manufacturer’s facilities and only TOC values drawn from the 305.5/312.5 nm wavelength combination were compared with the satellite data. The mean bias deviation between MICROTOPS II and OMI satellite data sets was obtained to be less than 2%, and the mean absolute deviation was in the range of 5%. The difference in the mean seasonal TOC values in summer and autumn was less than 0.5%, while in winter and spring this difference reached 2.8%. A possible calibration of MICROTOPS II instrument with the satellite data is presented, where the calibration coefficients for all channels were calculated for every satellite and MICROTPS II data pair during one year. Then, the average value of all the calculated coefficients was used for instrument calibration. The presented calibration improves the MICROTOPS II instrument stability and enables the usage of all the wavelength combinations.

An update on ozone profile trends for the period 2000 to 2016

Abstract. Ozone profile trends over the period 2000 to 2016 from several merged satellite ozone data sets and from ground-based data measured by four techniques at stations of the Network for the Detection of Atmospheric Composition Change indicate significant ozone increases in the upper stratosphere, between 35 and 48 km altitude (5 and 1 hPa). Near 2 hPa (42 km), ozone has been increasing by about 1.5 % per decade in the tropics (20° S to 20° N), and by 2 to 2.5 % per decade in the 35 to 60° latitude bands of both hemispheres. At levels below 35 km (5 hPa), 2000 to 2016 ozone trends are smaller and not statistically significant. The observed trend profiles are consistent with expectations from chemistry climate model simulations. This study confirms positive trends of upper stratospheric ozone already reported, e.g., in the WMO/UNEP Ozone Assessment 2014 or by Harris et al. (2015). Compared to those studies, three to four additional years of observations, updated and improved data sets with reduced drift, and the fact that nearly all individual data sets indicate ozone increase in the upper stratosphere, all give enhanced confidence. Uncertainties have been reduced, for example for the trend near 2 hPa in the 35 to 60° latitude bands from about ±5 % (2σ) in Harris et al. (2015) to less than ±2 % (2σ). Nevertheless, a thorough analysis of possible drifts and differences between various data sources is still required, as is a detailed attribution of the observed increases to declining ozone-depleting substances and to stratospheric cooling. Ongoing quality observations from multiple independent platforms are key for verifying that recovery of the ozone layer continues as expected.

Sensitivity of the tropical stratospheric ozone response to the solar rotational cycle in observations and chemistry–climate model simulations

Abstract. The tropical stratospheric ozone response to solar UV variations associated with the rotational cycle (∼ 27 days) is analyzed using MLS satellite observations and numerical simulations from the LMDz-Reprobus chemistry–climate model. The model is used in two configurations, as a chemistry-transport model (CTM) where dynamics are nudged toward ERA-Interim reanalysis and as a chemistry–climate model (free-running) (CCM). An ensemble of five 17-year simulations (1991–2007) is performed with the CCM. All simulations are forced by reconstructed time-varying solar spectral irradiance from the Naval Research Laboratory Solar Spectral Irradiance model. We first examine the ozone response to the solar rotational cycle during two 3-year periods which correspond to the declining phases of solar cycle 22 (October 1991–September 1994) and solar cycle 23 (September 2004–August 2007), when the satellite ozone observations of the two Microwave Limb Sounders (UARS MLS and Aura MLS) are available. In the observations, during the first period, ozone and UV flux are found to be correlated between about 10 and 1 hPa with a maximum of 0.29 at ∼ 5 hPa; the ozone sensitivity (% change in ozone for 1 % change in UV) peaks at ∼ 0.4. Correlation during the second period is weaker and has a peak ozone sensitivity of only 0.2, possibly due to the fact that the solar forcing is weaker during that period. The CTM simulation reproduces most of these observed features, including the differences between the two periods. The CCM ensemble mean results comparatively show much smaller differences between the two periods, suggesting that the amplitude of the rotational ozone signal estimated from MLS observations or the CTM simulation is strongly influenced by other (non-solar) sources of variability, notably dynamics. The analysis of the ensemble of CCM simulations shows that the estimation of the ensemble mean ozone sensitivity does not vary significantly either with the amplitude of the solar rotational fluctuations or with the size of the time window used for the ozone sensitivity retrieval. In contrast, the uncertainty of the ozone sensitivity estimate significantly increases during periods of decreasing amplitude of solar rotational fluctuations (also coinciding with minimum phases of the solar cycle), and for decreasing size of the time window analysis. We found that a minimum of 3- and 10-year time window is needed for the 1σ uncertainty to drop below 50 and 20 %, respectively. These uncertainty sources may explain some of the discrepancies found in previous estimates of the ozone response to the solar rotational cycle.