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Narrow field-of view spectral measurements of twilight sky brightness as a function of solar zenith angle in the 89°-95° range allow to retrieve lower stratospheric and tropospheric aerosol extinction profiles. The measurements were carried out over Tbilisi, Georgia, South Caucasus during 2021-2022 in the 700-800 nm wavelength range using a SBIG ST9 CCD camera and a SBIG SGS spectrograph. The Monte Carlo code Siro, developed in the Finnish Meteorological Institute was used to design a forward model. Aerosol extinction profiles at 780 nm were retrieved using the Levenberg–Marquardt algorithm.Stratospheric aerosol loading was low in the considered period whereas the upper (about 9-10 km) and lower troposphere (about 4-5 km) were sometimes disturbed due to small volcanic eruptions and dust transport events. Particularly, ash clouds from Etna eruptions on 10 and 21 February were observed at about 9 km altitude.

A comprehensive inter-comparison of seven radiative transfer models in the limb scattering geometry has been performed. Every model is capable of accounting for polarization within a spherical atmosphere. Three models (GSLS, SASKTRAN-HR, and SCIATRAN) are deterministic, and four models (MYSTIC, SASKTRAN-MC, Siro, and SMART-G) are statistical using the Monte Carlo technique. A wide variety of test cases encompassing different atmospheric conditions, solar geometries, wavelengths, tangent altitudes, and Lambertian surface reflectances have been defined and executed for every model. For the majority of conditions it was found that the models agree to better than 0.2 % in the single-scatter test cases and better than 1 % in the scalar and vectorial test cases with multiple scattering included, with some larger differences noted at high values of surface reflectance. For the first time in limb geometry, the effect of atmospheric refraction was compared among four models that support it (GSLS, SASKTRAN-HR, SCIATRAN, and SMART-G). Differences among most models with multiple scattering and refraction enabled were less than 1 %, with larger differences observed for some models. Overall the agreement among the models with and without refraction is better than has been previously reported in both scalar and vectorial modes.

Twilight sky brightness spectral measurements are an inexpensive and effective way to observe enhancements of stratospheric aerosols. In this work, we present our observations of the volcanic cloud produced by the eruption of Raikoke volcano (Kuril Islands, 48°N, 153°E) above two distinct sites in South Caucasus and Western Europe, respectively: Tbilisi, Georgia (41° 43’ N, 44° 47° E) and Halle, Belgium (50° 44′ N, 4° 14′ E).We present our dataset, which describes the evolution of the stratospheric aerosol in the period July 2019-December 2020. Stratospheric aerosol vertical extinction profiles were retrieved at 780 nm from spectral measurements of twilight sky brightness above both sites.The first aerosols originating from Raikoke were observed in the beginning of July above Halle and in August above Georgia. The layer maximum was mostly observed at 17 km above Georgia and at 10-17 km above Belgium until April-May 2020. Later, the volcanic cloud was observed sporadically until the end of 2020.

In this paper, we present the MErged GRIdded Dataset of Ozone Profiles (MEGRIDOP) in the stratosphere with a resolved longitudinal structure, which is derived from data from six limb and occultation satellite instruments: GOMOS, SCIAMACHY and MIPAS on Envisat, OSIRIS on Odin, OMPS on Suomi-NPP, and MLS on Aura. The merged dataset was generated as a contribution to the European Space Agency Climate Change Initiative Ozone project (Ozone_cci). The period of this merged time series of ozone profiles is from late 2001 until the end of 2018. The monthly mean gridded ozone profile dataset is provided in the altitude range from 10 to 50 km in bins of 10∘ latitude × 20∘ longitude. The merging is performed using deseasonalized anomalies. The created MEGRIDOP dataset can be used for analyses that probe our understanding of stratospheric chemistry and dynamics. To illustrate some possible applications, we created a climatology of ozone profiles with resolved longitudinal structure. We found zonal asymmetry in the climatological ozone profiles at middle and high latitudes associated with the polar vortex. At northern high latitudes, the amplitude of the seasonal cycle also has a longitudinal dependence. The MEGRIDOP dataset has also been used to evaluate regional vertically resolved ozone trends in the stratosphere, including the polar regions. It is found that stratospheric ozone trends exhibit longitudinal structures at Northern Hemisphere middle and high latitudes, with enhanced trends over Scandinavia and the Atlantic region. This agrees well with previous analyses and might be due to changes in dynamical processes related to the Brewer–Dobson circulation.

Raikoke volcano (Kuril Islands, Russia) eruption on 21 June 2019 sent an ash plume at 10-13 km altitude, which is higher than the local tropopause. Volcanic aerosols were transported around the globe, causing spectacular purple twilights. We will present ground-based measurements of monochromatic twilight sky brightnesses at 780 nm wavelength in two geographical points: Tbilisi, Georgia (41° 43’ N, 44° 47° E) and Halle, Belgium (50° 44′ N, 4° 14′ E). Aerosol extinction vertical profiles in the lower stratosphere-upper troposphere were retrieved with the help of the Levenberg–Marquardt algorithm. Monte Carlo code Siro was used to design a forward model. Raikoke aerosols observed above the both sites have shown essentially cloudy and variable structure. Multiple layers were observed between 10 and 17 km with extinction up to 0.01 km-1. We will present Raikoke aerosol cloud evolution in the period July 2019 –January 2020.

Most of our understanding of the atmosphere is based on observations and their comparison with model simulations. In middle atmosphere studies it is common practice to use an approach, where the model dynamics are at least partly based on temperature and wind fields from an external meteorological model. In this work we test how closely satellite measurements of a few central trace gases agree with this kind of model simulation. We use collocated vertical profiles where each satellite measurement is compared to the closest model data. We compare profiles and distributions of O3, NO2 and NO3 from the Global Ozone Monitoring by Occultation of Stars instrument (GOMOS) on the Envisat satellite with simulations by the Whole Atmosphere Community Climate Model (WACCM). GOMOS measurements are from nighttime. Our comparisons show that in the stratosphere outside the polar regions differences in ozone between WACCM and GOMOS are small, between 0 and 6%. The correlation of 5-day time series show a very high 0.9–0.95. In the tropical region 10° S–10° N below 10 hPa WACCM values are up to 20 % larger than GOMOS. In the Arctic below 6 hPa WACCM ozone values are up to 20 % larger than GOMOS. In the mesosphere between 0.04 and 1 hPa the WACCM is at most 20 % smaller than GOMOS. Above the ozone minimum at 0.01 hPa (or 80 km) large differences are found between WACCM and GOMOS. The correlation can still be high, but at the second ozone peak the correlation falls strongly and the ozone abundance from WACCM is about 60 % smaller than that from GOMOS. The total ozone columns (above 50 hPa) of GOMOS and WACCM agree within ±2 % except in the Arctic where WACCM is 10 % larger than GOMOS. Outside the polar areas and in the validity region of GOMOS NO2 measurements (0.3–37 hPa) WACCM and GOMOS NO2 agree within −5 to +25 % and the correlation is high (0.7–0.95) except in the upper stratosphere at the southern latitudes. In the polar areas, where solar particle precipitation and downward transport from the thermosphere enhance NO2 abundance, large differences up to −90 % are found between WACCM and GOMOS NO2 and the correlation varies between 0.3 and 0.9. For NO3, we find that the WACCM and GOMOS difference is between −20 and 5 % with a very high correlation of 0.7–0.95. We show that NO3 values strongly depend on temperature and the dependency can be fitted by the exponential function of temperature. The ratio of NO3 to O3 from WACCM and GOMOS closely follow the prediction from the equilibrium chemical theory. Abrupt temperature increases from sudden stratospheric warmings (SSWs) are reflected as sudden enhancements of WACCM and GOMOS NO3 values.

Observations taken over the last few decades indicate that dramatic changes are occurring in the ArcticBoreal Zone (ABZ), which are having significant impacts on ABZ inhabitants, infrastructure, flora and fauna, and economies. While suitable for detecting overall change, the current capability is inadequate for systematic monitoring and for improving processbased and largescale understanding of the integrated components of the ABZ, which includes the cryosphere, biosphere, hydrosphere, and atmosphere. Such knowledge will lead to improvements in Earth system models, enabling more accurate prediction of future changes and development of informed adaptation and mitigation strategies. In Duncan et al. (2020), we review the strengths and limitations of current spacebased observational capabilities for several important ABZ components and make recommendations for improving upon these current capabilities. We recommend an interdisciplinary and stepwise approach to develop a comprehensive ABZ Observing Network (ABZON), beginning with an initial focus on observing networks designed to gain processbased understanding for individual ABZ components and systems that can then serve as the building blocks for a comprehensive ABZON.

International audience; Global Ozone Monitoring by Occultation of Stars (GOMOS) on board Envisat has performed about 440 000 night-time occultations during 2002–2012. Self-calibrating measurement principle, good vertical resolution, excellent pointing accuracy and the wide vertical range from the troposphere up to the lower thermosphere make GOMOS profiles interesting for different analyses. The GOMOS ozone data are of high quality in the stratosphere and the mesosphere, but the current operational retrieval algorithm (IPF v.6) is not optimized for retrievals in the upper troposphere–lower stratosphere (UTLS). In particular, validation of GOMOS profiles against ozonesonde data has revealed a substantial positive bias (up to 100 %) in the UTLS region. The retrievals in the UTLS are challenging because of low signal-to-noise ratio and the presence of clouds. In this work, we discuss the reasons for the systematic uncertainties in the UTLS with the IPF v.6 algorithm or its modifications based on simultaneous retrievals of several constituents using the full visible wavelength range. The main reason is high sensitivity of the UTLS retrieval algorithms to an assumed aerosol extinction model. We have developed a new aerosol–insensitive ozone profile inversion algorithm for GOMOS data in the UTLS using a DOAS-type method at visible wavelengths. The method uses minimal assumptions about the atmospheric profiles. The ozone retrievals in the whole altitude range from the troposphere to the lower thermosphere are performed in two steps, as in the operational algorithm: spectral inversion followed by the vertical inversion. The horizontal column ozone densities retrieved in the spectral inversion follow V6 profiles in the middle atmosphere and follow the triplet ozone profiles in the UTLS. The vertical inversion is performed as in IPF v6 with the Tikhonov-type regularization according to the target resolution. The validation of new retrieved ozone profiles with ozonesondes show dramatic reduction of GOMOS ozone biases in the UTLS. The new GOMOS ozone profiles are also in a very good agreement with measurements by MIPAS, ACE-FTS and OSIRIS satellite instruments in the UTLS. It is also shown that the known geophysical phenomena in the UTLS ozone are well reproduced with the new GOMOS data.

The GOMOS instrument on Envisat has successfully demonstrated that a UV–Vis–NIR spaceborne stellar occultation instrument is capable of delivering quality data on the gaseous and particulate composition of Earth's atmosphere. Still, some problems related to data inversion remained to be examined. In the past, it was found that the aerosol extinction profile retrievals in the upper troposphere and stratosphere are of good quality at a reference wavelength of 500 nm but suffer from anomalous, retrieval-related perturbations at other wavelengths. Identification of algorithmic problems and subsequent improvement was therefore necessary. This work has been carried out; the resulting AerGOM Level 2 retrieval algorithm together with the first data version AerGOMv1.0 forms the subject of this paper. The AerGOM algorithm differs from the standard GOMOS IPF processor in a number of important ways: more accurate physical laws have been implemented, all retrieval-related covariances are taken into account, and the aerosol extinction spectral model is strongly improved. Retrieval examples demonstrate that the previously observed profile perturbations have disappeared, and the obtained extinction spectra look in general more consistent. We present a detailed validation study in a companion paper; here, to give a first idea of the data quality, a worst-case comparison at 386 nm shows SAGE II–AerGOM correlation coefficients that are up to 1 order of magnitude larger than the ones obtained with the GOMOS IPFv6.01 data set.

Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere (as measured by equivalent effective stratospheric chlorine – EESC) was maximised in the second half of the 1990s. We examine the periods before and after the peak to see if any change in trend is discernible in the ozone record that might be attributable to a change in the EESC trend, though no attribution is attempted. Prior to 1998, trends in the upper stratosphere (~ 45 km, 4 hPa) are found to be −5 to −10 % per decade at mid-latitudes and closer to −5 % per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However, it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the main satellite and ground-based records have been revised. There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~ 2 % per decade in mid-latitudes and ~ 3 % per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different data sets. The averaged upward trends are significant if the trends derived from various data sets are assumed to be independent (as in Pawson et al., 2014) but are generally not significant if the trends are not independent. This occurs because many of the underlying measurement records are used in more than one merged data set. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties.

We have created a daytime ozone profile data set from the measurements of the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the Envisat satellite. This so-called GOMOS bright limb (GBL) data set contains ∼ 358 000 stratospheric daytime ozone profiles measured by GOMOS in 2002–2012. The GBL data set complements the widely used GOMOS nighttime data based on stellar occultation measurements. The GBL data set is based on the GOMOS daytime occultations but instead of the transmitted star light we use limb-scattered solar light. The ozone profiles retrieved from these radiance spectra cover the 18–60 km altitude range and have approximately 2–3 km vertical resolution. We show that these profiles are generally in better than 10 % agreement with the NDACC (Network for the Detection of Atmospheric Composition Change) ozonesonde profiles and with the GOMOS nighttime, MLS (Microwave Limb Sounder), and OSIRIS (Optical Spectrograph and InfraRed Imager System) satellite measurements. However, there is a 10–13 % negative bias at 40 km altitude and a 10–50 % positive bias at 50 km for solar zenith angles > 75°. These biases are most likely caused by stray light which is difficult to characterize and to remove entirely from the measured spectra. Nevertheless, the GBL data set approximately doubles the amount of useful GOMOS ozone profiles and improves coverage of the summer pole.

In the framework of the SI2N (SPARC (Stratosphere-troposphere Processes And their Role in Climate)/IO3C (International Ozone Commission)/IGACO-O3 (Integrated Global Atmospheric Chemistry Observations – Ozone)/NDACC (Network for the Detection of Atmospheric Composition Change)) initiative, several long-term vertically resolved merged ozone data sets produced from satellite measurements have been analysed and compared. This paper presents an overview of the methods, assumptions, and challenges involved in constructing such merged data sets, as well as the first thorough intercomparison of seven new long-term satellite data sets. The analysis focuses on the representation of the annual cycle, interannual variability, and long-term trends for the period 1984–2011, which is common to all data sets. Overall, the best agreement amongst data sets is seen in the mid-latitude lower and middle stratosphere, with larger differences in the equatorial lower stratosphere and the upper stratosphere globally. In most cases, differences in the choice of underlying instrument records that were merged produced larger differences between data sets than the use of different merging techniques. Long-term ozone trends were calculated for the period 1984–2011 using a piecewise linear regression with a change in trend prescribed at the end of 1997. For the 1984–1997 period, trends tend to be most similar between data sets (with largest negative trends ranging from −4 to −8% decade−1 in the mid-latitude upper stratosphere), in large part due to the fact that most data sets are predominantly (or only) based on the SAGE-II record. Trends in the middle and lower stratosphere are much smaller, and, particularly for the lower stratosphere, large uncertainties remain. For the later period (1998–2011), trends vary to a greater extent, ranging from approximately −1 to +5% decade−1 in the upper stratosphere. Again, middle and lower stratospheric trends are smaller and for most data sets not significantly different from zero. Overall, however, there is a clear shift from mostly negative to mostly positive trends between the two periods over much of the profile., Atmospheric Chemistry and Physics, 15 (6), ISSN:1680-7375, ISSN:1680-7367

We have studied data from two satellite occultation instruments in order to generate a high vertical resolution homogeneous ozone time series of 26 yr. The Stratospheric Aerosol and Gas Experiment (SAGE) II solar occultation instrument and the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument measured ozone profiles in the stratosphere and mesosphere from 1984–2005 and 2002–2012, respectively. Global coverage, good vertical resolution, and the self-calibrating measurement method make data from these instruments valuable for the detection of changes in vertical distribution of ozone over time. As both instruments share a common measurement period from 2002–2005, it is possible to inter-calibrate the data sets. We investigate how well these measurements agree with each other and combine all the data to produce a new stratospheric ozone profile data set. Above 55 km, SAGE II measurements show much less ozone than the GOMOS nighttime measurements as a consequence of the well-known diurnal variation of ozone in the mesosphere. Between 35–55 km, SAGE II sunrise and sunset measurements differ from GOMOS' measurements to different extents. Sunrise measurements show 2% less ozone than GOMOS, whereas sunset measurements show 4% more ozone than GOMOS. Differences can be explained qualitatively by the diurnal variation of ozone in the stratosphere recently observed by SMILES and modeled by chemical transport models. Between 25–35 km, SAGE II sunrise and sunset measurements and GOMOS measurements agree within 1%. The observed ozone bias between collocated measurements of SAGE II sunrise/sunset and GOMOS night measurements is used to align the two data sets. The combined data set covers the time period 1984–2011, latitudes 60° S–60° N, and the altitude range of 20–60 km. Profile data are given on a 1 km vertical grid, and with a resolution of 1 month in time and 10° in latitude. The combined ozone data set is analyzed by fitting a time series model to the data. We assume a linear trend with an inflection point (so-called "hockey stick" form). The best estimate for the point of inflection was found to be the year 1997 for ozone between altitudes 35 and 45 km. At all latitudes and altitudes from 35 to 50 km we find a clear change in ozone trend before and after the inflection time. From 38 to 45 km, a negative trend of 4% per decade (statistically significant at 95% level) at the equator has changed to a small positive trend of 0–2% per decade. At mid-latitudes, the negative trend of 4–8% per decade has changed to to a small positive trend of 0–2% per decade. At mid-latitudes near 20 km, the ozone loss has still increased whereas in the tropics a recovery is ongoing.

The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European platform ENVISAT (ENVironment SATellite) was dedicated to the study of the of Earth's atmosphere using the stellar occultation technique. The spectral range of the GOMOS spectrometer extends from the UV (ultra violet) to the near infrared, allowing for the retrieval of species such as O3, NO2, NO3, H2O, O2, air density, aerosol extinction and OClO. Nevertheless, OClO cannot be retrieved using a single GOMOS measurement because of the weak signal-to-noise ratio and the small optical thickness associated with this molecule. We present here the method used to detect this molecule by using several GOMOS measurements. It is based on a two-step approach. First, several co-located measurements are combined in a statistical way to build an averaged measurement with a higher signal-to-noise ratio; then, a differential optical absorption spectroscopy (DOAS) method is applied to retrieve OClO slant column densities (SCD). The statistics of the sets of GOMOS measurements used to build the averaged measurement and the spectral window selection are analyzed. The obtained retrievals are compared to results from two balloon-borne instruments. It appears that the inter-comparisons of OClO are generally satisfying (relative differences are about 15–60%). Two nighttime climatologies of OClO based on GOMOS averaged measurements are presented. The first depicts annual global pictures of OClO from 2003 to 2011. From this climatology, the presence of an OClO SCD peak in the equatorial region at about 35 km is confirmed and strong OClO SCD in both polar regions are observed (more than 1016 cm−2 in the Antarctic region and slightly less in the Arctic region), a sign of chlorine activation. The second climatology is a monthly time series. It clearly shows the chlorine activation of the lower stratosphere during winter. Moreover the equatorial OClO SCD peak is observed during all years without any significant variations. This very promising method, applied on GOMOS measurements, allowed us to build the first nighttime climatology of OClO using limb-viewing instruments.

[1] The link between stratospheric ozone decline and ultraviolet (UV) radiation increase at the Earth's surface is well established. In the Northern Hemisphere extratropics, stratospheric ozone is accumulated from autumn to spring as a result of transport from its source region in the tropics. The amount of accumulated ozone varies from year to year due to natural dynamical variability and chemical destruction by natural and anthropogenic substances. Observational and modeling studies show that these total ozone anomalies persist in the extratropics from spring to summer. Here we analyze time series of ground-based UV measurements and satellite retrievals of total ozone and UV radiation and demonstrate that there is a strong link between springtime total ozone and summer UV anomalies in the Northern Hemisphere extratropics. In some regions, the interannual variability in springtime ozone abundance explains 20–40% of the summer UV variability, and this relation can be used for improving seasonal UV forecasts. Using chemistry transport models, we estimate the influence of polar chemical ozone loss on the summer UV north of 35°N. We estimate that the massive Arctic ozone depletion 2011 increased the March–August cumulative erythemal clear-sky UV dose in the Northern Hemisphere extratropics by 3–4% compared to the climatology, with about 75% of the increase accumulated after the breakup of the polar vortex. This result strongly suggests that the effect of seasonal ozone anomaly persistence should be included in the assessment of the impacts of polar ozone losses.

Observations of the mesospheric semi-annual oscillation (MSAO) in the equatorial region have been reported dating back several decades. Seasonal variations in both species densities and airglow emissions are well documented. The extensive observations available offer an excellent case study for comparison with model simulations. A broad range of MSAO measurements is summarised with emphasis on the 80–100 km region. The objective here is not to address directly the complicated driving forces of the MSAO, but rather to employ a combination of observations and model simulations to estimate the limits of some of the underlying dynamical processes. Photochemical model simulations are included for near-equinox and near-solstice conditions, the two times with notable differences in the observed MSAO parameters. Diurnal tides are incorporated in the model to facilitate comparisons of observations made at different local times. The roles of water vapour as the "driver" species and ozone as the "response" species are examined to test for consistency between the model results and observations. The simulations suggest the interactions between vertical eddy diffusion and background vertical advection play a significant role in the MSAO phenomenon. Further, the simulations imply there are rigid limits on vertical advection rates and eddy diffusion rates. For August at the Equator, 90 km altitude, the derived eddy diffusion rate is approximately 1 × 106 cm2 s−1 and the vertical advection is upwards at 0.8 cm s−1. For April the corresponding values are 4 × 105 cm2 s−1 and 0.1 cm s−1. These results from the current 1-D model simulations will need to be verified by a full 3-D simulation. Exactly how vertical advection and eddy diffusion are related to gravity wave momentum as discussed by Dunkerton (1982) three decades ago remains to be addressed.

[1] Here we use satellite observations from the ACE-FTS, MLS/Aura and SABER/TIMED to study the effects of solar proton events (SPEs) and strong sudden stratospheric warmings (SSWs) on the middle atmospheric odd nitrogen (NOx) and ozone levels in the Northern Hemispheric polar region. Three winters (January–March) are considered: (1) 2005 (SPE), (2) 2009 (SSW), and (3) 2012 (SPEs and SSW). These different cases provide a good opportunity to study the roles that transport from the mesosphere-lower thermosphere region and in situ production due to particle precipitation have on stratospheric NOx levels and the consequent effects on the middle atmospheric ozone. The observations show increases in NOx after both the SPEs (days to weeks) and SSWs (weeks to months) by up to a factor of 25 between 40 and 90 km. The largest mesospheric NOx increases are observed following the SSW in late January 2009, but the most substantial effects in the upper stratosphere are seen when both an SSW and in situ production by SPEs take place (2012), even though the in situ NOx production in 2012 was relatively weak in magnitude compared to periods of much higher solar activity. In 2012, both short-term (days, due to SPEs and odd hydrogen) depletion and longer-term (months, due to several drivers) depletion of ozone of up to 90% are observed in the mesosphere and upper stratosphere, coinciding with the enhanced amounts of NOx.

In this paper, we present a HARMonized dataset of OZone profiles (HARMOZ) based on limb and occultation measurements from Envisat (GOMOS, MIPAS and SCIAMACHY), Odin (OSIRIS, SMR) and SCISAT (ACE-FTS) satellite instruments. These measurements provide high-vertical-resolution ozone profiles covering the altitude range from the upper troposphere up to the mesosphere in years 2001–2012. HARMOZ has been created in the framework of the European Space Agency Climate Change Initiative project. The harmonized dataset consists of original retrieved ozone profiles from each instrument, which are screened for invalid data by the instrument teams. While the original ozone profiles are presented in different units and on different vertical grids, the harmonized dataset is given on a common pressure grid in netCDF (network common data form)-4 format. The pressure grid corresponds to vertical sampling of ~ 1 km below 20 km and 2–3 km above 20 km. The vertical range of the ozone profiles is specific for each instrument, thus all information contained in the original data is preserved. Provided altitude and temperature profiles allow the representation of ozone profiles in number density or mixing ratio on a pressure or altitude vertical grid. Geolocation, uncertainty estimates and vertical resolution are provided for each profile. For each instrument, optional parameters, which are related to the data quality, are also included. For convenience of users, tables of biases between each pair of instruments for each month, as well as bias uncertainties, are provided. These tables characterize the data consistency and can be used in various bias and drift analyses, which are needed, for instance, for combining several datasets to obtain a long-term climate dataset. This user-friendly dataset can be interesting and useful for various analyses and applications, such as data merging, data validation, assimilation and scientific research. The dataset is available at http://www.esa-ozone-cci.org/?q=node/161 or at doi:10.5270/esa-ozone_cci-limb_occultation_profiles-2001_2012-v_1-201308.

Global Ozone Monitoring by Occultation of Stars (GOMOS) on board Envisat has performed about 440 000 night-time occultations during 2002–2012. Self-calibrating measurement principle, good vertical resolution, excellent pointing accuracy and the wide vertical range from the troposphere up to the lower thermosphere make GOMOS profiles interesting for different analyses. The GOMOS ozone data are of high quality in the stratosphere and the mesosphere, but the current operational retrieval algorithm (IPF v.6) is not optimized for retrievals in the upper troposphere–lower stratosphere (UTLS). In particular, validation of GOMOS profiles against ozonesonde data has revealed a substantial positive bias (up to 100 %) in the UTLS region. The retrievals in the UTLS are challenging because of low signal-to-noise ratio and the presence of clouds. In this work, we discuss the reasons for the systematic uncertainties in the UTLS with the IPF v.6 algorithm or its modifications based on simultaneous retrievals of several constituents using the full visible wavelength range. The main reason is high sensitivity of the UTLS retrieval algorithms to an assumed aerosol extinction model. We have developed a new aerosol–insensitive ozone profile inversion algorithm for GOMOS data in the UTLS using a DOAS-type method at visible wavelengths. The method uses minimal assumptions about the atmospheric profiles. The ozone retrievals in the whole altitude range from the troposphere to the lower thermosphere are performed in two steps, as in the operational algorithm: spectral inversion followed by the vertical inversion. The horizontal column ozone densities retrieved in the spectral inversion follow V6 profiles in the middle atmosphere and follow the triplet ozone profiles in the UTLS. The vertical inversion is performed as in IPF v6 with the Tikhonov-type regularization according to the target resolution. The validation of new retrieved ozone profiles with ozonesondes show dramatic reduction of GOMOS ozone biases in the UTLS. The new GOMOS ozone profiles are also in a very good agreement with measurements by MIPAS, ACE-FTS and OSIRIS satellite instruments in the UTLS. It is also shown that the known geophysical phenomena in the UTLS ozone are well reproduced with the new GOMOS data.

Peak stratospheric chlorofluorocarbon (CFC) and other ozone depleting substance (ODS) concentrations were reached in the mid- to late 1990s. Detection and attribution of the expected recovery of the stratospheric ozone layer in an atmosphere with reduced ODSs as well as efforts to understand the evolution of stratospheric ozone in the presence of increasing greenhouse gases are key current research topics. These require a critical examination of the ozone changes with an accurate knowledge of the spatial (geographical and vertical) and temporal ozone response. For such an examination, it is vital that the quality of the measurements used be as high as possible and measurement uncertainties well quantified. In preparation for the 2014 United Nations Environment Programme (UNEP)/World Meteorological Organization (WMO) Scientific Assessment of Ozone Depletion, the SPARC/IO3C/IGACO-O3/NDACC (SI2N) Initiative was designed to study and document changes in the global ozone profile distribution. This requires assessing long-term ozone profile data sets in regards to measurement stability and uncertainty characteristics. The ultimate goal is to establish suitability for estimating long-term ozone trends to contribute to ozone recovery studies. Some of the data sets have been improved as part of this initiative with updated versions now available. This summary presents an overview of stratospheric ozone profile measurement data sets (ground and satellite based) available for ozone recovery studies. Here we document measurement techniques, spatial and temporal coverage, vertical resolution, native units and measurement uncertainties. In addition, the latest data versions are briefly described (including data version updates as well as detailing multiple retrievals when available for a given satellite instrument). Archive location information for each data set is also given.

The GOMOS instrument on EnviSat has succesfully demonstrated that a UV/Vis/NIR spaceborne stellar occultation instrument is capable of delivering quality data on the gaseous and particulate composition of Earth's atmosphere. Still, some problems related to data inversion remained to be treated. In the past, it was found that the aerosol extinction profile retrievals in the upper troposphere and stratosphere are of good quality at a reference wavelength of 500 nm, but suffer from anomalous, retrieval-related perturbations at other wavelengths. Identification of algorithmic problems and subsequent improvement was therefore necessary. This work has been carried out; the resulting AerGOM Level 2 retrieval algorithm together with the first data version AerGOMv1.0 forms the subject of this paper. First, a brief overview of the operational IPFv6.01 GOMOS algorithm is given, since the AerGOM algorithm is to a certain extent similar. Then, the discussion on the AerGOM algorithm specifically focuses on the new aspects that were implemented to tackle the aerosol retrieval problems. Finally, a first assess- ment of the obtained aerosol extinction data quality is presented, clearly showing significant improvement of aerosol profile shape, spectral behaviour and similarity to SAGE II data.

In this paper, we present the first global comparisons between the two unique satellite-borne data sets of nitrogen trioxide (NO3) vertical profiles retrieved from the GOMOS (Global Ozone Monitoring by the Occultation of Stars) stellar occultations and the SAGE III (Stratospheric Aerosol and Gas Experiment) lunar occultations. The comparison results indicate that between the altitudes 25 km and 45 km the median difference between these two data sets is within ± 25%. The study of zonal median profiles shows that the climatologies calculated from GOMOS and SAGE III profiles are comparable and represent the same features in all latitude bands. No clear systematic differences are observed. The median profiles are closest in the tropics and slightly deviating at high latitudes.

A large zonal asymmetry of ozone has been observed over Antarctica during winter-spring, when the ozone hole develops. It is caused by a planetary wave-driven displacement of the polar vortex. The total ozone data by OMI (Ozone Monitoring Instrument) and the ozone profiles by MLS (Microwave Limb Sounder) and GOMOS (Global Ozone Monitoring by Occultation of Stars) were analysed to characterize the ozone zonal asymmetry and the wave activity during Antarctic spring. Both total ozone and profile data have shown a persistent zonal asymmetry over the last years, which is usually observed from September to mid-December. The largest amplitudes of planetary waves at 65° S (the perturbations can achieve up to 50% of zonal mean values) is observed in October. The wave activity is dominated by the quasi-stationary wave 1 component, while the wave 2 is mainly an eastward travelling wave. Wave numbers 1 and 2 generally explain more than the 90% of the ozone longitudinal variations. Both GOMOS and MLS ozone profile data show that ozone zonal asymmetry covers the whole stratosphere and extends up to the altitudes of 60–65 km. The wave amplitudes in ozone mixing ratio decay with altitude, with maxima (up to 50%) below 30 km. The characterization of the ozone zonal asymmetry has become important in the climate research. The inclusion of the polar zonal asymmetry in the climate models is essential for an accurate estimation of the future temperature trends. This information might also be important for retrieval algorithms that rely on ozone a priori information.

Sudden stratospheric warmings (SSW) are large-scale transient events, which have a profound effect on the Northern Hemisphere stratospheric circulation in winter. During the SSW events the temperature in stratosphere increases by several tens of Kelvins and zonal winds decelerate or reverse in direction. Changes in temperature and dynamics significantly affect the chemical composition of the middle atmosphere. In this paper, the response of the middle-atmosphere trace gases during several sudden stratospheric warmings in 2003–2008 is investigated using measurements from the GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite. We have analyzed spatial and temporal changes of NO2 and NO3 in the stratosphere, and of ozone in the whole middle atmosphere. To facilitate our analyses, we have used the temperature profiles data from the MLS (Microwave Limb Sounder) instrument on board the Aura satellite, as well as simulations by the FinROSE chemistry-transport model and the Sodankylä Ion and Neutral Chemistry model (SIC). NO3 observations in the polar winter stratosphere during SSWs are reported for the first time. Changes in chemical composition are found not to be restricted to the stratosphere, but to extend to mesosphere and lower thermosphere. They often exhibit a complicated structure, because the distribution of trace gases is affected by changes in both chemistry and dynamics. The tertiary ozone maximum in the mesosphere often disappears with the onset of SSW, probably because of strong mixing processes. The strong horizontal mixing with outside-vortex air is well observed also in NO2 data, especially in cases of enhanced NO2 inside the polar vortex before SSW. Almost in all of the considered events, ozone near the secondary maximum decreases with onset of SSW. In both experimental data and FinROSE modelling, ozone changes are positively correlated with temperature changes in the lower stratosphere in the dynamically controlled region below ~35 km, and they are negatively correlated with temperature in the upper stratosphere (altitudes 35–50 km), where chemical processes play a significant role. Large enhancements of stratospheric NO3, which strongly correlate with temperature enhancements, are observed for all SSWs, as expected by the current understanding of temperature-dependence of NO3 concentrations and simulations with the CTM.

The quasi-biennial oscillation (QBO) and semi-annual oscillation (SAO) characteristics of O3, NO2, and NO3 from 2002 to 2008 were analyzed using Global Ozone Monitoring by Occultation of Stars (GOMOS) satellite observations. From investigations of the vertical and latitudinal structures of interannual anomalies for O3 and the vertical velocity of the residual circulation (w-star), we conclude that dynamic transport is the principal factor controlling the QBO pattern of O3. Under the influence of vertical transport, the QBO signals of O3 originate in the middle stratosphere and propagate downward along with the w-star anomalies over the equator. The residual circulation has a significant role in tropical regions, regardless of altitude, while in extratropical regions, dynamic effects are important in some years in the lower stratosphere. In the middle stratosphere, dynamic transport is most efficient in the Southern Hemisphere. We also analyzed NO2 anomalies and found that their QBO pattern was deep and stationary in the middle and upper stratosphere over the equator. This was due to the large depth over which w-star was anomalous. The latitudinal structure of NO2 was asymmetric in extratropical areas in the middle stratosphere, but in the upper layers, the QBO pattern and dynamic influences were only observed in tropical zones. The interannual anomalies of NO3 had an apparent SAO pattern in the tropical upper stratosphere because of different dynamic and chemical effects in different SAO phases. Chemical reactions may also have contributed to the QBO-type distribution of NO2 and the SAO-type distribution of NO3.

We use the 3-D FinROSE chemistry transport model (CTM) and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) observations to study connections between atmospheric dynamics and middle atmospheric NOx (NOx = NO + NO2) distribution. Two cases are considered in the northern polar regions: (1) descent of mesospheric NOx in February–March 2009 after a major sudden stratospheric warming (SSW) and, for comparison, (2) early 2007 when no NOx descent occurred. The model uses the European Centre for Medium-Range Weather Forecasts (ECMWF) operational data for winds and temperature, and we force NOx at the model upper altitude boundary (80 km) with ACE-FTS observations. We then compare the model results with ACE-FTS observations at lower altitudes. For the periods studied, geomagnetic indices are low, which indicates absence of local NOx production by particle precipitation. This gives us a good opportunity to study effects of atmospheric transport on polar NOx. The model results show no NOx descent in 2007, in agreement with ACE-FTS. In contrast, a large amount of NOx descends in February–March 2009 from the upper to lower mesosphere at latitudes larger than 60° N, i.e. inside the polar vortex. Both observations and model results suggest NOx increases of 150–200 ppb (i.e. by factor of 50) at 65 km due to the descent. However, the model underestimates the amount of NOx around 55 km by 40–60 ppb. According to the model results, chemical loss of NOx is insignificant during the descent period, i.e. polar NOx is mainly controlled by dynamics. The descent is terminated and the polar NOx amounts return to pre-descent levels in mid-March, when the polar vortex breaks. The break-up prevents the descending NOx from reaching the upper stratosphere, where it could participate in catalytic ozone destruction. Both ACE-FTS observations and FinROSE show a decrease of ozone of 20–30 % at 30–50 km from mid-February to mid-March. In the model, these ozone changes are not related to the descent but are due to solar activation of halogen and NOx chemistry.

The stellar occultation spectrometer GOMOS (Global Ozone Monitoring by Occultation of Stars) on ESA's Envisat satellite measures vertical profiles O3, NO2 and NO3 with a high long-term stability due to the self-calibrating nature of the technique. More than 6 years of GOMOS data from August 2002 to end 2008 have been analysed to study the inter-annual variation of O3, NO2 and NO3 in the tropics. It is shown that the QBO of the equatorial wind induces variations in the local concentration larger than 10% for O3 and larger than 25% for NO2. Quasi-Biennial Oscillation signals can be found in the evolution of the three constituents up to at least 45 km. We found that NO3 is positively correlated with temperature up to 40 km in the region where it is in chemical equilibrium with O3. Above 40 km, NO3 is no more in equilibrium during night and its concentration is correlated with both O3 and NO2. For O3 and NO2, our results confirm the existence of a transition from a dynamical control of O3 below 28 km with O3 correlated with NO2 and temperature and a chemical/temperature control between 28 and 38 km with O3 anti-correlated with NO2 and temperature. Above 38 km and up to 50 km a regime never described before is found with both O3 and NO2 anti-correlated with temperature. For the NO2/temperature anti-correlation, our proposed explanation is the modulation of the N2O ascent in the upper stratosphere by the QBO and the modulation of the Brewer-Dobson circulation. The oxidation of N2O is the main source of NOy in this altitude region. An enhancement of the ascending motion will cool adiabatically the atmosphere and will increase the amount of N2O concentration available for NOy formation.

Although the retrieval of aerosol extinction coefficients from satellite remote measurements is notoriously difficult (in comparison with gaseous species) due to the lack of typical spectral signatures, important information can be obtained. In this paper we present an overview of the current operational nighttime UV/Vis aerosol extinction profile results for the GOMOS star occultation instrument, spanning the period from August 2002 to May 2008. Some problems still remain, such as the ones associated with incomplete scintillation correction and the aerosol spectral law implementation, but good quality extinction values are obtained at a wavelength of 500 nm. Typical phenomena associated with atmospheric particulate matter in the Upper Troposphere/Lower Stratosphere (UTLS) are easily identified: Polar Stratospheric Clouds, tropical subvisual cirrus clouds, background stratospheric aerosols, and post-eruption volcanic aerosols (with their subsequent dispersion around the globe). For the first time, we show comparisons of GOMOS 500 nm particle extinction profiles with the ones of other satellite occultation instruments (SAGE II, SAGE III and POAM III), of which the good agreement lends credibility to the GOMOS data set. Yearly zonal statistics are presented for the entire period considered. Time series furthermore convincingly show an important new finding: the sensitivity of GOMOS to the sulfate input by moderate volcanic eruptions such as Manam (2005) and Soufrière Hills (2006). Finally, PSCs are well observed by GOMOS and a first qualitative analysis of the data agrees well with the theoretical PSC formation temperature. Therefore, the importance of the GOMOS aerosol/cloud extinction profile data set is clear: a long-term data record of PSCs, subvisual cirrus, and background and volcanic aerosols in the UTLS region, consisting of hundreds of thousands of altitude profiles with near-global coverage, with the potential to fill the aerosol/cloud extinction data gap left behind after the discontinuation of occultation instruments such as SAGE II, SAGE III and POAM III.

This paper presents extensive validation analyses of ozone observations from the Atmospheric Chemistry Experiment (ACE) satellite instruments: the ACE Fourier Transform Spectrometer (ACE-FTS) and the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) instrument. The ACE satellite instruments operate in the mid-infrared and ultraviolet-visible-near-infrared spectral regions using the solar occultation technique. In order to continue the long-standing record of solar occultation measurements from space, a detailed quality assessment is required to evaluate the ACE data and validate their use for scientific purposes. Here we compare the latest ozone data products from ACE-FTS and ACE-MAESTRO with coincident observations from satellite-borne, airborne, balloon-borne and ground-based instruments, by analysing volume mixing ratio profiles and partial column densities. The ACE-FTS version 2.2 Ozone Update product reports more ozone than most correlative measurements from the upper troposphere to the lower mesosphere. At altitude levels from 16 to 44 km, the mean differences range generally between 0 and +10% with a slight but systematic positive bias (typically +5%). At higher altitudes (45-60 km), the ACE-FTS ozone amounts are significantly larger than those of the comparison instruments by up to ~40% (typically +20%). For the ACE-MAESTRO version 1.2 ozone data product, agreement within ±10% (generally better than ±5%) is found between 18 and 40 km for the sunrise and sunset measurements. At higher altitudes (45-55 km), systematic biases of opposite sign are found between the ACE-MAESTRO sunrise and sunset observations. While ozone amounts derived from the ACE-MAESTRO sunrise occultation data are often smaller than the coincident observations (by as much as -10%), the sunset occultation profiles for ACE-MAESTRO show results that are qualitatively similar to ACE-FTS and indicate a large positive bias (+10 to +30%) in this altitude range. In contrast, there is no significant difference in bias found for the ACE-FTS sunrise and sunset measurements. These systematic effects in the ozone profiles retrieved from the measurements of ACE-FTS and ACE-MAESTRO are being investigated. This work shows that the ACE instruments provide reliable, high quality measurements from the tropopause to the upper stratosphere and can be used with confidence in this vertical domain

The ozone profile records of a large number of limb and occultation satellite instruments are widely used to address several key questions in ozone research. Further progress in some domains depends on a more detailed understanding of these data sets, especially of their long-term stability and their mutual consistency. To this end, we made a systematic assessment of 14 limb and occultation sounders that, together, provide more than three decades of global ozone profile measurements. In particular, we considered the latest operational Level-2 records by SAGE II, SAGE III, HALOE, UARS MLS, Aura MLS, POAM II, POAM III, OSIRIS, SMR, GOMOS, MIPAS, SCIAMACHY, ACE-FTS and MAESTRO. Central to our work is a consistent and robust analysis of the comparisons against the ground-based ozonesonde and stratospheric ozone lidar networks. It allowed us to investigate, from the troposphere up to the stratopause, the following main aspects of satellite data quality: long-term stability, overall bias and short-term variability, together with their dependence on geophysical parameters and profile representation. In addition, it permitted us to quantify the overall consistency between the ozone profilers. Generally, we found that between 20 and 40 km the satellite ozone measurement biases are smaller than ±5 %, the short-term variabilities are less than 5–12 % and the drifts are at most ±5 % decade−1 (or even ±3 % decade−1 for a few records). The agreement with ground-based data degrades somewhat towards the stratopause and especially towards the tropopause where natural variability and low ozone abundances impede a more precise analysis. In part of the stratosphere a few records deviate from the preceding general conclusions; we identified biases of 10 % and more (POAM II and SCIAMACHY), markedly higher single-profile variability (SMR and SCIAMACHY) and significant long-term drifts (SCIAMACHY, OSIRIS, HALOE and possibly GOMOS and SMR as well). Furthermore, we reflected on the repercussions of our findings for the construction, analysis and interpretation of merged data records. Most notably, the discrepancies between several recent ozone profile trend assessments can be mostly explained by instrumental drift. This clearly demonstrates the need for systematic comprehensive multi-instrument comparison analyses.

The activity “Absorption Cross-Sections of Ozone” (ACSO) started in 2008 as a joint initiative of the International Ozone Commission (IO3C), the World Meteorological Organization (WMO) and the IGACO (“Integrated Global Atmospheric Chemistry Observations”) O3/UV subgroup to study, evaluate, and recommend the most suitable ozone absorption cross-section laboratory data to be used in atmospheric ozone measurements. The evaluation was basically restricted to ozone absorption cross-sections in the UV range with particular focus on the Huggins band. Up until now, the data of Bass and Paur published in 1985 (BP, 1985) are still officially recommended for such measurements. During the last decade it became obvious that BP (1985) cross-section data have deficits for use in advanced space-borne ozone measurements. At the same time, it was recognized that the origin of systematic differences in ground-based measurements of ozone required further investigation, in particular whether the BP (1985) cross-section data might contribute to these differences. In ACSO, different sets of laboratory ozone absorption cross-section data (including their dependence on temperature) of the group of Reims (France) (Brion et al., 1993, 1998, 1992, 1995, abbreviated as BDM, 1995) and those of Serdyuchenko et al. (2014), and Gorshelev et al. (2014), (abbreviated as SER, 2014) were examined for use in atmospheric ozone measurements in the Huggins band. In conclusion, ACSO recommends: (a) The spectroscopic data of BP (1985) should no longer be used for retrieval of atmospheric ozone measurements. (b) For retrieval of ground-based instruments of total ozone and ozone profile measurements by the Umkehr method performed by Brewer and Dobson instruments data of SER (2014) are recommended to be used. When SER (2014) is used, the difference between total ozone measurements of Brewer and Dobson instruments are very small and the difference between Dobson measurements at AD and CD wavelength pairs are diminished. (c) For ground-based Light Detection and Ranging (LIDAR) measurements the use of BDM (1995) or SER (2014) is recommended. (d) For satellite retrieval the presently widely used data of BDM (1995) should be used because SER (2014) seems less suitable for retrievals that use wavelengths close to 300 nm due to a deficiency in the signal-to-noise ratio in the SER (2014) dataset. The work of ACSO also showed: • The need to continue laboratory cross-section measurements of ozone of highest quality. The importance of careful characterization of the uncertainties of the laboratory measurements. • The need to extend the scope of such studies to other wavelength ranges (particularly to cover not only the Huggins band but also the comparison with the mid-infrared region). • The need for regular cooperation of experts in spectral laboratory measurements and specialists in atmospheric (ozone) measurements.

Stratospheric O3 profiles obtained by the satellite limb sounders Aura/MLS, ENVISAT/MIPAS, ENVISAT/GOMOS, SAGE-II, SAGE-III, UARS/HALOE are compared to coincident O3 profiles of the ground-based microwave radiometer SOMORA in Switzerland. Data from the various measurement techniques are within 10% at altitudes below 45 km. At altitudes 45–60 km, the relative O3 differences are within a range of 50%. Larger deviations at upper altitudes are attributed to larger relative measurement errors caused by lower O3 concentrations. The spatiotemporal characteristics of the O3 differences (satellite – ground station) are investigated by analyzing about 2300 coincident profile pairs of Aura/MLS (retrieval version 1.5) and SOMORA. The probability density function of the O3 differences is represented by a Gaussian normal distribution. The dependence of the O3 differences on the horizontal distance between the sounding volumes of Aura/MLS and SOMORA is derived. While the mean bias (Aura/MLS – SOMORA) is constant with increasing horizontal distance (up to 800 km), the standard deviation of the O3 differences increases from around 8 to 11% in the mid-stratosphere. Geographical maps yield azimuthal dependences and horizontal gradients of the O3 difference field around the SOMORA ground station. Coherent oscillations of O3 are present in the time series of Aura/MLS and SOMORA (e.g., due to traveling planetary waves). Ground- and space-based measurements often complement one another. We discuss the double differencing technique which allows both the cross-validation of two satellites by means of a ground station and the cross-validation of distant ground stations by means of one satellite. Temporal atmospheric noise in the geographical ozone map over Payerne is significantly reduced by combination of the data from SOMORA and Aura/MLS. These analyses illustrate the synergy of ground-based and space-based measurements.

Interplanetary Lyman alpha line profiles are derived from the SWAN H cell data measurements. The measurements cover a 6-year period from solar minimum (1996) to after the solar maximum of 2001. This allows us to study the variations of the line profiles with solar activity. These line profiles were used to derive line shifts and line widths in the interplanetary medium for various angles of the LOS with the interstellar flow direction. The SWAN data results were then compared to an interplanetary background upwind spectrum obtained by STIS/HST in March 2001. We find that the LOS upwind velocity associated with the mean line shift of the IP \lya line varies from 25.7 km/s to 21.4 km/s from solar minimum to solar maximum. Most of this change is linked with variations in the radiation pressure. LOS kinetic temperatures derived from IP line widths do not vary monotonically with the upwind angle of the LOS. This is not compatible with calculations of IP line profiles based on hot model distributions of interplanetary hydrogen. We also find that the line profiles get narrower during solar maximum. The results obtained on the line widths (LOS temperature) show that the IP line is composed of two components scattered by two hydrogen populations with different bulk velocities and temperature. This is a clear signature of the heliospheric interface on the line profiles seen at 1 AU from the sun., Comment: 9 pages, 9 figures

We present first results of the analysis of fine details present in GOMOS co-added transmittances. In particular, mesospheric sodium (around 589 nm) and the oxygen green line (at 557 nm) have been unambiguously identified and the Na concentration profile can be obtained by standard inversion techniques. Two other unusual spectral signatures have been observed, both exhibiting a strong altitude dependence, in absorption (511.7 nm) and in emission (601.2 nm), the first one perhaps being related to a transition involving an excited state of molecular oxygen. The general usefulness of averaging limb transmittances data is discussed.

With the successful launch of the European Space Agency’s Envisat satellite new possibilities for global night-time measurements of middle atmospheric ozone have emerged. The GOMOS and MIPAS instruments on board Envisat are able to measure ozone in both day and night conditions, which is especially important in the mesosphere where the diurnal variations of ozone are substantial. In this paper, we present a comparison of MIPAS and GOMOS night-time measurements. We show individual measurement profiles as well as statistical average profiles of stratospheric and mesospheric ozone from both instruments. Our conclusion is that the two instruments are generally in a good agreement throughout the middle atmosphere.

In this work we discuss inclusion of a priori information about the smoothness of atmospheric profiles in inversion algorithms. The smoothness requirement can be formulated in the form of Tikhonov-type regularization, where the smoothness of atmospheric profiles is considered as a constraint or in the form of Bayesian optimal estimation (maximum a posteriori method, MAP), where the smoothness of profiles can be included as a priori information. We develop further two recently proposed retrieval methods. One of them - Tikhonov-type regularization according to the target resolution - develops the classical Tikhonov regularization. The second method - maximum a posteriori method with smoothness a priori - effectively combines the ideas of the classical MAP method and Tikhonov-type regularization. We discuss a grid-independent formulation for the proposed inversion methods, thus isolating the choice of calculation grid from the question of how strong the smoothing should be. The discussed approaches are applied to the problem of ozone profile retrieval from stellar occultation measurements by the GOMOS instrument on board the Envisat satellite. Realistic simulations for the typical measurement conditions with smoothness a priori information created from 10-years analysis of ozone sounding at Sodankylä and analysis of the total retrieval error illustrate the advantages of the proposed methods. The proposed methods are equally applicable to other profile retrieval problems from remote sensing measurements.

This paper discusses the smoothness of vertical profiles of ozone concentrations. We describe the smoothness of ozone profiles via a characteristic scale of the profile fluctuations. The characteristic scale was computed for 11-years (1989-1999) ozone sonde data at Sodankylä. Mean values of the characteristic scale were determined. They are ~1km in the troposphere and ~1.4km in the lower stratosphere (up to 25km). Only slight seasonal variations of these parameters are observed. The information about smoothness of ozone profiles is needed both in the instrumental design for defining the vertical resolution requirements and in the development of inversion algorithms from remote sensing measurements, in order to obtain the best accuracy in retrieved ozone profiles and sufficient resolution.

GOMOS (Global Ozone Monitoring by Occultation of Stars) on board Envisat measures O 3 , NO 2 , NO 3 , neutral density, aerosols, H 2 O, and O 2 , in the stratosphere and mesosphere by detecting absorption of starlight in ultraviolet, visible and near-infrared wavelengths. During bright limb conditions GOMOS will also observe scattered solar radiation. GOMOS will deliver ozone concentration profiles at altitudes 15–100 km with a vertical sampling better than 1.7 km and with a global coverage. As a self-calibrating method stellar occultation measurements provide a basis for a long-term global monitoring of ozone profiles. We will present here the status of the GOMOS instrument and show samples of first results obtained in 2002.

Based on SWAN/SOHO observations carried out during 1996-2002, we analyze latitudinal profiles of the helio- spheric backscatter Lyman- radiation. We use these results to investigate the ionization field of neutral hydrogen in the inner heliosphere and the latitudinal distribution of the solar wind mass flux. The the depth and latitudinal range of the equatorial depression in the Lyman- backscatter glow (the so-called "groove") are correlated with the corresponding parameters of the ionization field. We show that the groove is entirely due to latitudinal anisotropy of the solar wind, since, as we are able to demonstrate, the photoionization rate remains spherically symmetric throughout the solar cycle. During the last solar minimum the groove was well developed and stable. During the ascending phase of solar activity, it expanded in latitude (first south, then north), and disappeared altogether during the solar maximum. Shortly after the maximum it reappeared, but its structure was more complex than during the ascending phase. The groove feature is correlated with the equatorial band occupied by the slow solar wind, while the polar maxima of the Lyman- intensity correspond to the fast solar wind from the polar holes. The groove observations (supported by appropriate modeling) show that during the last solar minimum the mass flux of the fast solar wind from the north and south polar holes were dierent from each other: a true north-south asymmetry between the polar regions was detected. During the solar minimum, the area occupied by the slow solar wind was quite stable and oset slightly to the south with respect to the solar equator: it extended to about 30 N and 35S from the beginning of observations in May 1996 till 1998. Then it expanded by about 10 north and south, and subsequently migrated towards southern latitudes, so that it engulfed the south pole in May/June 2000. The north region of the fast wind survived longer and disappeared as late as November/December 2001. To check for the persistence of the north-south asymmetry, we analyze as a proxy the net sunspot area in the north and south hemispheres of the Sun during the 12 past solar cycles. Small north-south asymmetries are found to be commonplace during the past cycles, but the polarity of the asymmetries changes, leaving no statistically significant remnant asymmetry. This suggests that the solar dynamo is solely responsible for the asymmetry, with no remnant magnetic field from the protosolar nebula.

Odin is a satellite with a combined astronomy and aeronomy mission. It is designed for observations of species dicult or impossible to observe from ground, especially water and oxygen. The main instrument is a radiometer, operating in the frequency range 486-581 GHz and at 118.75 GHz. Its double-reflector telescope has a 1.1 m primary and the front-end amplifiers are cooled for maximum sensitivity. A 3-axis-stabilisation system provides a pointing accuracy better than 10 00 .O din was developed on behalf of the space agencies in Sweden, Canada, France and Finland and was launched into a sun synchronous circular orbit in February 2001. The Odin Science Team, composed of astronomers and aeronomers from the partner countries, has established the observing programme and is responsible for all scientific matters regarding the Odin project. The spacecraft and instruments are performing well and operations are expected to continue well beyond the nominal two-year lifetime.

Stratospheric ozone profile measurements from the Stratospheric Aerosol and Gas Experiment~(SAGE) II satellite instrument (1984–2005) are combined with those from the Optical Spectrograph and InfraRed Imager System (OSIRIS) instrument on the Odin satellite (2001–Present) to quantify interannual variability and decadal trends in stratospheric ozone between 60° S and 60° N. These data are merged into a multi-instrument, long-term stratospheric ozone record (1984–present) by analyzing the measurements during the overlap period of 2002–2005 when both satellite instruments were operational. The variability in the deseasonalized time series is fit using multiple linear regression with predictor basis functions including the quasi-biennial oscillation, El Niño–Southern Oscillation index, solar activity proxy, and the pressure at the tropical tropopause, in addition to two linear trends (one before and one after 1997), from which the decadal trends in ozone are derived. From 1984 to 1997, there are statistically significant negative trends of 5–10% per decade throughout the stratosphere between approximately 30 and 50 km. From 1997 to present, a statistically significant recovery of 3–8% per decade has taken place throughout most of the stratosphere with the notable exception between 40° S and 40° N below approximately 22 km where the negative trend continues. The recovery is not significant between 25 and 35 km altitudes when accounting for a conservative estimate of instrument drift.

The water production rates of comets 2P/Encke and 81P/Wild 2 during their 1997 apparitions have been estimated from Lyman-α observations of the SWAN instrument and compared to previously published values. 2P/Encke was detected 28 times from few days preperihelion to 1.4 AU postperihelion with a perihelion water production rate QH2O of 2×1028 s−1. This is the first observation of perihelion QH2O of comet Encke. 81P/Wild 2 was detected 56 times from 1.64 AU preperihelion to 1.74 AU postperihelion with a perihelion QH2O of 1.3×1028 s−1.