Polar Ozone And Aerosol Measurement Research Articles

Updated merged SAGE-CCI-OMPS+ dataset for the evaluation of ozone trends in the stratosphere

Abstract. In this paper, we present the updated SAGE-CCI-OMPS+ climate data record of monthly zonal mean ozone profiles. This dataset covers the stratosphere and combines measurements by nine limb and occultation satellite instruments – SAGE II (Stratospheric Aerosol and Gases Experiment II), OSIRIS (Optical Spectrograph and InfraRed Imaging System), MIPAS (Michelson Interferometer for Passive Atmospheric Sounding), SCIAMACHY (SCanning Imaging Spectrometer for Atmospheric CHartographY), GOMOS (Global Ozone Monitoring by Occultation of Stars), ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer), OMPS-LP (Ozone Monitor Profiling Suite Limb Profiler), POAM (Polar Ozone and Aerosol Measurement) III, and SAGE III/ISS (Stratospheric Aerosol and Gases Experiment III on the International Space Station). Compared to the original version of the SAGE-CCI-OMPS dataset (Sofieva et al., 2017b), the update includes new versions of MIPAS, ACE-FTS, and OSIRIS datasets and introduces data from additional sensors (POAM III and SAGE III/ISS) and retrieval processors (OMPS-LP). In this paper, we show detailed intercomparisons of ozone profiles from different instruments and data versions, with a focus on the detection of possible drifts in the datasets. The SAGE-CCI-OMPS+ dataset has a better coverage of polar regions and of the upper troposphere and the lower stratosphere (UTLS) than the previous dataset. We also studied the influence of including new datasets on ozone trends, which are estimated using multiple linear regression. The changes in the merged dataset do not change the overall morphology of post-1997 ozone trends; statistically significant trends are observed in the upper stratosphere. The largest changes in ozone trends are observed in polar regions, especially in the Southern Hemisphere. The updated SAGE-CCI-OMPS+ dataset contains profiles of deseasonalized anomalies and ozone concentrations from 1984 to 2021, in 10∘ latitude bins from 90∘ S to 90∘ N and in the altitude range from 10 to 50 km. The dataset is open access and available at https://climate.esa.int/en/projects/ozone/data/ (last access: 9 March 2023) and at ftp://cci_web@ftp-ae.oma.be/esacci (ESA Climate Office; last access: 9 March 2023).

Ozone loss rates in the Arctic winter stratosphere during 1994-2000 derived from POAM II/III and ILAS observations: Implications for relationships among ozone loss, PSC occurrence, and temperature

[1] Quantitative chemical ozone loss rates at the 475 K isentropic surface inside the Arctic polar vortex are evaluated for six winters (January through March) using a satellite-based Match technique. Satellite observational data are taken from the Polar Ozone and Aerosol Measurement (POAM) II for 1994–1996, the Improved Limb Atmospheric Spectrometer (ILAS) for 1997, and the POAM III for 1999–2000. The largest ozone loss rates were observed in the end of January 1995 (∼50 ± 20 ppbv d−1), February 1996 (∼40–50 ± 15 ppbv d−1), February 1997 (∼40 ± 8 ppbv d−1), January 2000 (∼60 ± 30 ppbv d−1), and early March 2000 (∼40 ± 10 ppbv d−1). The probability of polar stratospheric cloud (PSC) existence is estimated using aerosol extinction coefficient data from POAM II/III and ILAS. Ozone loss and the PSC probability are strongly correlated and an absolute increase of 10% in the PSC probability is found to amplify the chemical ozone loss rate during Arctic winter by approximately 25 ± 6 ppbv per day or 3.2 ± 0.7 ppbv per sunlit hour. Relationships between average Arctic winter ozone loss rates and various PSC- and temperature-related indices are investigated, including the area of polar vortex that is colder than the threshold temperature for PSC existence (APSC), the PSC formation potential (PFP), and the potential for activation of chlorine (PACl). Of these three, PACl provides the best proxy representation of interannual variability in Arctic ozone loss at the 475 K level. Large ozone loss occurred primarily for air masses that experienced low temperatures between 187 K and 195 K within the previous 10 days and the ozone loss rates clearly increase with decreasing the minimum temperature. The particularly large ozone losses of ∼9 ± 3 ppbv per sunlit hour in February 1996 and January 2000 were associated with low minimum temperatures of 187–189 K, simultaneously with high PSC probabilities.

Ten years of Southern Hemisphere polar mesospheric cloud observations from the Polar Ozone and Aerosol Measurement instruments

Polar mesospheric clouds (PMCs) were observed in the Southern Hemisphere by both the Polar Ozone and Aerosol Measurement (POAM) II and III instruments. POAM II operated from 1993 to 1996 and its three seasons of Southern Hemisphere PMC observations were previously reported by Debrestian et al. (1997a, 1997b). POAM III operated from 1998 to 2005 and thus observed PMCs during seven Southern Hemisphere seasons. The two POAM instruments are in identical orbits and are very similar in design and measurement capability. These similarities allow for the application of a common PMC detection algorithm to generate a consistent long‐term data record by combining the two POAM data sets. In this paper we present an analysis of this combined data set, which consists of approximately 670 PMC observations. The seasonally averaged PMC occurrence frequency, when adjusted for differences in detection sensitivity of the instruments, is found to be strongly anticorrelated with the solar Lyman‐α flux. The POAM PMC profiles were analyzed using a geometrical cloud model to determine cloud height, vertical thickness, and wavelength‐dependent extinction. Seasonally averaged cloud altitudes range from 82.6 to 83.5 km and the thickness varies between approximately 2 and 3 km. The multiwavelength capability of the POAM III instrument has been used to derive information on PMC particle sizes using the spectral dependence of the measured slant path optical depth. The results of this analysis indicate a mean value of 52 nm for the PMC optically effective radius, which is consistent with a variety of other observations.

Ice polar stratospheric clouds detected from assimilation of Atmospheric Infrared Sounder data

A novel technique is presented for the detection and mapping of ice polar stratospheric clouds (PSCs), using brightness temperatures from the Atmospheric Infrared Sounder (AIRS) “moisture” channel near 6.79 μm. It is based on observed‐minus‐forecast residuals (O‐Fs) computed when using AIRS radiances in the Goddard Earth Observing System version 5 (GEOS‐5) data assimilation system. Brightness temperatures are computed from six‐hour GEOS‐5 forecasts using a radiation transfer module under clear‐sky conditions, meaning they will be too high when ice PSCs are present. We study whether the O‐Fs contain quantitative information about PSCs by comparison with sparse data from the Polar Ozone and Aerosol Measurement (POAM) III solar occultation instrument. AIRS O‐Fs lower than −2 K generally coincide with PSCs observed by POAM III. Synoptic maps of AIRS O‐Fs lower than −2 K are constructed as a proxy for ice PSCs. These are used to investigate spatio‐temporal variations of Antarctic PSCs in the year 2004.

The onboard imagers for the Canadian ACE SCISAT‐1 mission

The Atmospheric Chemistry Experiment (ACE) onboard the Canadian Space Agency’s SCISAT‐1 satellite has been in orbit since August of 2003. Its broad objective is to study the problem of stratospheric ozone depletion, particularly in the Arctic. The main instruments are two spectrometers, one an infrared Fourier Transform Spectrometer and the other a dual optical spectrophotometer sensitive in the UV and visible. Also included are two filtered imagers used to measure altitude profiles of atmospheric extinction and detect thin clouds. The nominal center wavelengths of the filters are 525 nm for the visible (VIS) imager and 1020 nm for the near‐infrared (NIR) imager. With the decommissioning of other satellite instruments used to monitor global aerosols [i.e., Stratospheric Aerosol and Gas Experiment II (SAGE II), SAGE III, Polar Ozone and Aerosol Measurement (POAM) III, Halogen Occultation Experiment (HALOE)], the imagers provide much needed continuity in this data record. The data product from the imagers is still, however, in a preliminary state. Funding restrictions in the prelaunch period were responsible for an incomplete characterization of the imagers’ optics and electronics and prevented corrections being made for the problems found during testing. Postlaunch data analysis to correct for image artifacts is ongoing. A comparison with coincidental measurements from SAGE II shows that systematic errors from the preliminary analysis are within 5 and 20% for the VIS and NIR imagers, respectively, for uninverted profiles of optical depth. Despite the preliminary nature of the imager results, a paper describing the imagers and the initial operational data processing code is timely because the data are already being used.

Validation of Odin/OSIRIS stratospheric NO2 profiles

This paper presents the validation study of stratospheric NO2 profiles retrieved from Odin/OSIRIS measurements of limb‐scattered sunlight (version 2.4). The Optical Spectrograph and Infrared Imager System (OSIRIS) NO2 data set is compared to coincident solar occultation measurements by the Halogen Occultation Experiment (HALOE), Stratospheric Aerosol and Gas Experiment (SAGE) II, SAGE III, and Polar Ozone and Aerosol Measurement (POAM) III during the 2002–2004 period. Comparisons with seven Systeme d'Analyse par Observation Zenithal (SAOZ) balloon measurements are also presented. All comparisons show good agreement, with differences, both random and systematic, of less than 20% between 25 km and 35 km. Inconsistencies with SAGE III below 25 km are found to be caused primarily by diurnal effects from varying NO2 concentrations along the SAGE III line‐of‐sight. On the basis of the differences, the OSIRIS random uncertainty is estimated to be 16% between 15 km and 25 km, 6% between 25 km and 35 km, and 9% between 35 km and 40 km. The estimated systematic uncertainty is about 22% between 15 and 25 km, 11–21% between 25 km and 35 km, and 11–31% between 35 km and 40 km. The uncertainties for AM (sunrise) profiles are generally largest and systematic deviations are found to be larger at equatorial latitudes. The results of this validation study show that the OSIRIS NO2 profiles are well behaved, with reasonable uncertainty estimates between 15 km and 40 km. This unique NO2 data set, with more than hemispheric coverage and high vertical resolution will be of particular interest for studies of nitrogen chemistry in the middle atmosphere, which is closely linked to ozone depletion.

Polar stratospheric clouds in the 1998–2003 Antarctic vortex: Microphysical modeling and Polar Ozone and Aerosol Measurement (POAM) III observations

The Integrated Microphysics and Aerosol Chemistry on Trajectories (IMPACT) model is used to study polar stratospheric cloud (PSC) formation and evolution in the Antarctic vortex. The model is applied to individual air parcel trajectories driven by UK Met Office (UKMO) wind and temperature fields. The IMPACT model calculates the parcel microphysics, including the formation and sedimentation of ice, nitric acid trihydrate (NAT), sulfuric acid tetrahydrate (SAT), and supercooled ternary solution (STS) aerosols. Model results are validated by comparison with data obtained by the Polar Ozone and Aerosol Measurement (POAM) III solar occultation instrument and are examined for 6 years of POAM data (1998–2003). Comparisons of POAM water vapor and aerosol extinction measurements to the model results help to constrain three microphysical parameters influencing the formation and growth of both type I and type II PSCs. Principally, measurements of aerosol extinction prove to be valuable in differentiating model runs; the relationship of aerosol extinction to temperature is determined by the various particle types as they form and grow. Comparison of IMPACT calculations of this relationship to POAM measurements suggests that the initial fraction of nuclei available for heterogeneous NAT freezing is approximately 0.02% of all aerosols. Constraints are also placed on the accommodation coefficient of ice and the NAT‐ice lattice compatibility. However, these two parameters have similar effects on the extinction‐temperature relationship, and thus a range of values are permissible for each.

Validation of Polar Ozone and Aerosol Measurement (POAM) III version 4 stratospheric water vapor

The Polar Ozone and Aerosol Measurement (POAM) III solar occultation instrument has been measuring water vapor at high latitudes since April 1998. Retrievals extend from 5 to 50 km, with 5–7% precision throughout the stratosphere and a vertical resolution of 1 (3) km in the lower (upper) stratosphere. Estimated systematic errors in the stratosphere are 10–15%. In this paper, we validate the POAM III version 4 stratospheric water vapor using correlative measurements from satellite, airborne, and balloon‐borne platforms. The resulting comparisons show that POAM water vapor is high compared to correlative measurements in the middle to lower stratosphere. The satellite (Halogen Occultation Experiment (HALOE) and Stratospheric Aerosol and Gas Experiment (SAGE) II) comparisons also indicate a sunrise/sunset bias in the POAM data, with sunset (Southern Hemisphere) retrievals larger than sunrise (Northern Hemisphere) retrievals by 5–10%. In the Northern Hemisphere, POAM is approximately 5–10% high compared to all validation data sets between 12 and 35 km. At higher altitudes this difference decreases, such that POAM agrees with HALOE at 40 km and is lower by 10% at 50 km. In the Southern Hemisphere, POAM is 15–25% higher than HALOE below 35 km, with differences decreasing to 10% by 50 km. Similar differences are seen with SAGE II. Despite these systematic differences the POAM water vapor data are self‐consistent and show no long‐term trends in accuracy or precision. Statistical comparisons of the water vapor variability measured by POAM, HALOE, and SAGE II show very good agreement. The POAM data are therefore valid for scientific studies, and the science community is encouraged to use this unique data set.

Microphysical modeling of southern polar dehydration during the 1998 winter and comparison with POAM III observations

Stratospheric dehydration and high aerosol extinctions are examined for the 1998 Antarctic winter using the Integrated Microphysics and Aerosol Chemistry on Trajectories (IMPACT) model and data obtained by the Polar Ozone and Aerosol Measurement (POAM) III instrument. The model is applied to individual air parcels which are advected along 3‐D trajectories using the United Kingdom Meteorological Office (UKMO) global wind and temperature fields. Model results are compared to water vapor and aerosol extinction measurements obtained with the POAM instrument. Results suggest that the water vapor mixing ratio at the end of the season is predicted with reasonable accuracy. However, dehydration occurs more rapidly in the simulation than is indicated by the POAM data. In addition to dehydration results, the frequency of high aerosol extinction measurements is examined for all model runs and compared to POAM data. The aerosol extinction comparisons are consistent with the assumption that heterogeneous nitric acid trihydrate (NAT) freezing occurs in approximately 1% of all particles. Various model parameters influencing ice cloud microphysics are altered to examine their effects on both the water vapor mixing ratio and high aerosol extinction events. While a reduction in the ice accommodation coefficient and an increase in the ice nucleation barrier both improve the agreement in the water vapor mixing ratio, the agreement in aerosol extinction is worsened. Extinction comparisons suggest that the model results are consistent with either high or low NAT‐ice lattice compatibility factors, although intermediate values agree poorly with POAM data. The extent of dehydration is highly dependent on temperature; therefore, an uncertainty as small as ±1 K in the UKMO temperature fields may significantly change the model results.

Fast Ozone Loss Around the Polar Vortex During 2002/2003 Arctic Winter Deep Minihole Event

A three-dimensional (3D) off-line chemical transport model (CTM) has been used to study an Arctic ozone minihole event in early December 2002, when the meteorological conditon were severely colder than in recent years. The minimum temperatures were below 188 K on 6 December 2002 and remained below 195 K for the entire month. Such temperatures are low enough for the formation of PSCs (polar stratospheric clouds) which were observed by a visible/near infrared solar occultation instrument by the Polar Ozone and Aerosol Measurement (POAM) III experiment. The SLIMCAT model compares well with the depth and evolution of the ozone distribution as observed by the second European Remote Sensing Satellite (ERS-2) Global Ozone Monitoring Experiment (GOME). The combined effect of a very strong and large intrusion of sub-tropical air, and uplifting of air masses of low ozone concentrations from the troposphere plays important role in the fomation of the ozone minihole. The modelled chemical ozone loss rate was relatively fast in the lower stratosphere in the region of frequent PSCs and higher levels of ClO and BrO. The observed PSCs in the vicinity of the minihole supports the model-predicted location of PSCs and chlorine activation. However, ozone miniholes have been attributed almost entirely to dynamical effects due to its short duration.

Retrieval of ozone column content from airborne Sun photometer measurements during SOLVE II: comparison with coincident satellite and aircraft measurements

Abstract. During the 2003 SAGE (Stratospheric Aerosol and Gas Experiment) III Ozone Loss and Validation Experiment (SOLVE) II, the fourteen-channel NASA Ames Airborne Tracking Sunphotometer (AATS-14) was mounted on the NASA DC-8 aircraft and measured spectra of total and aerosol optical depth (TOD and AOD) during the sunlit portions of eight science flights. Values of ozone column content above the aircraft have been derived from the AATS-14 measurements by using a linear least squares method that exploits the differential ozone absorption in the seven AATS-14 channels located within the Chappuis band. We compare AATS-14 columnar ozone retrievals with temporally and spatially near-coincident measurements acquired by the SAGE III and the Polar Ozone and Aerosol Measurement (POAM) III satellite sensors during four solar occultation events observed by each satellite. RMS differences are 19 DU (7% of the AATS value) for AATS-SAGE and 10 DU (3% of the AATS value) for AATS-POAM. In these checks of consistency between AATS-14 and SAGE III or POAM III ozone results, the AATS-14 analyses use airmass factors derived from the relative vertical profiles of ozone and aerosol extinction obtained by SAGE III or POAM III. We also compare AATS-14 ozone retrievals for measurements obtained during three DC-8 flights that included extended horizontal transects with total column ozone data acquired by the Total Ozone Mapping Spectrometer (TOMS) and the Global Ozone Monitoring Experiment (GOME) satellite sensors. To enable these comparisons, the amount of ozone in the column below the aircraft is estimated either by assuming a climatological model or by combining SAGE and/or POAM data with high resolution in-situ ozone measurements acquired by the NASA Langley Research Center chemiluminescent ozone sensor, FASTOZ, during the aircraft vertical profile at the start or end of each flight. Resultant total column ozone values agree with corresponding TOMS and GOME measurements to within 10-15 DU (~3%) for AATS data acquired during two flights - a longitudinal transect from Sweden to Greenland on 21 January, and a latitudinal transect from 47° N to 35° N on 6 February. For the round trip DC-8 latitudinal transect between 34° N and 22° N on 19-20 December 2002, resultant AATS-14 ozone retrievals plus below-aircraft ozone estimates yield a latitudinal gradient that is similar in shape to that observed by TOMS and GOME, but resultant AATS values exceed the corresponding satellite values by up to 30 DU at certain latitudes. These differences are unexplained, but they are attributed to spatial and temporal variability that was associated with the dynamics near the subtropical jet but was unresolved by the satellite sensors. For selected cases, we also compare AATS-14 ozone retrievals with values derived from coincident measurements by the other two DC-8 based solar occultation instruments: the National Center for Atmospheric Research Direct beam Irradiance Airborne Spectrometer (DIAS) and the NASA Langley Research Center Gas and Aerosol Monitoring System (GAMS). AATS and DIAS retrievals agree to within RMS differences of 1% of the AATS values for the 21 January and 19-20 December flights, and 2.3% for the 6 February flight. Corresponding AATS-GAMS RMS differences are ~1.5% for the 21 January flight; GAMS data were not compared for the 6 February flight and were not available for the 19-20 December flight. Line of sight ozone retrievals from coincident measurements obtained by the three DC-8 solar occultation instruments during the SAGE III solar occultation event on 24 January yield RMS differences of 2.1% for AATS-DIAS and 0.5% for AATS-GAMS.

2002-2003 Arctic ozone loss deduced from POAM III satellite observations and the SLIMCAT chemical transport model

Abstract. The SLIMCAT three-dimensional chemical transport model (CTM) is used to infer chemical ozone loss from Polar Ozone and Aerosol Measurement (POAM) III observations of stratospheric ozone during the Arctic winter of 2002-2003. Inferring chemical ozone loss from satellite data requires quantifying ozone variations due to dynamical processes. To accomplish this, the SLIMCAT model was run in a "passive" mode from early December until the middle of March. In these runs, ozone is treated as an inert, dynamical tracer. Chemical ozone loss is inferred by subtracting the model passive ozone, evaluated at the time and location of the POAM observations, from the POAM measurements themselves. This "CTM Passive Subtraction" technique relies on accurate initialization of the CTM and a realistic description of vertical/horizontal transport, both of which are explored in this work. The analysis suggests that chemical ozone loss during the 2002-2003 winter began in late December. This loss followed a prolonged period in which many polar stratospheric clouds were detected, and during which vortex air had been transported to sunlit latitudes. A series of stratospheric warming events starting in January hindered chemical ozone loss later in the winter of 2003. Nevertheless, by 15 March, the final date of the analysis, ozone loss maximized at 425K at a value of about 1.2ppmv, a moderate amount of loss compared to loss during the unusually cold winters in the late-1990s. SLIMCAT was also run with a detailed stratospheric chemistry scheme to obtain the model-predicted loss. The SLIMCAT model simulation also shows a maximum ozone loss of 1.2ppmv at 425K, and the morphology of the loss calculated by SLIMCAT was similar to that inferred from the POAM data. These results from the recently updated version of SLIMCAT therefore give a much better quantitative description of polar chemical ozone loss than older versions of the same model. Both the inferred and modeled loss calculations show the early destruction in late December and the region of maximum loss descending in altitude through the remainder of the winter and early spring.

The Climatology Of The Polar Aerosol From The Poam Instruments

We present a climatology of the high-latitude stratospheric aerosol derived from the multiwavelength extinction data of the POAM (Polar Ozone and Aerosol Measurement) II and III instruments from 1993 to 2003. Stratospheric aerosols north of 54°N and south of 63°S were continually monitored by POAM II between September 1993 and November 1996. These data clearly show the decay of the volcanic aerosol from the Pinatubo eruption which was still evident when the spacecraft ceased operation at the end of 1996. POAM III was launched into a similar orbit in March 1998 and has monitored the seasonal variation in the aerosol layer since its recovery to background levels. Extinction data from these two instruments at six wavelengths from the ultraviolet to near-infrared are combined through principal component analysis to yield total aerosol surface-area and volume densities. The temporal and spatial evolution of these physical parameters, which can be employed in chemistry and climate models, are presented and analyzed.

On the distribution of ozone in stratospheric anticyclones

Twelve years (1991–2003) of satellite occultation ozone data are combined with a climatology of stratospheric anticyclones and polar vortices to quantify the climatological ozone differences between air mass types. Ozone data from the Stratospheric Aerosol and Gas Experiment (SAGE) II, the Halogen Occultation Experiment (HALOE), the Polar Ozone and Aerosol Measurement (POAM) II and III missions, and the Improved Limb Atmospheric Spectrometer (ILAS) sensor are used in this study. Daily ozone measurements in the 400–1600 K altitude range are categorized as being either (1) in an anticyclone, (2) in a polar vortex, or (3) in neither (hereinafter referred to as “ambient”). Monthly mean ozone is then calculated in each air mass category from data combined over all years. This study focuses on ozone differences between anticyclones and the ambient environment. A composite annual cycle of ozone in ambient regions is compared to ozone in anticyclones as a function of altitude and latitude. Ozone differences result from both anomalous transport and photochemistry in the vicinity of stratospheric anticyclones. The relative importance of transport versus chemistry is inferred from the long‐term ozone anomalies observed here. In summer, ozone gradients between different air mass types are small. In other seasons, results indicate three distinct vertical regimes at high latitudes. Below ≈600 K, anticyclones coincide with regions where ozone is reduced by 10–50% during the winter. Between 600 and 900 K from fall to midwinter, anticyclones are associated with ≈10% more ozone than ambient air masses. Positive ozone anomalies are also observed in low‐latitude anticyclones within this vertical layer; however, they are half the size of their high‐latitude counterparts and peak several months later. Above 900 K the abundance of ozone in anticyclones is ≈10% less than in the surrounding air. This upper stratospheric regime results from the formation of “low‐ozone pockets” (LOPs) in stratospheric anticyclones. All LOPs that formed between November 1991 and November 2003 and were observed by a satellite used in this study (108 pockets) are documented here in the most comprehensive catalog of LOPs to date.

Retrieval of nitrogen dioxide stratospheric profiles from ground-based zenith-sky UV-visible observations: validation of the technique through correlative comparisons

Abstract. A retrieval algorithm based on the Optimal Estimation Method (OEM) has been developed in order to provide vertical distributions of NO2 in the stratosphere from ground-based (GB) zenith-sky UV-visible observations. It has been applied to observational data sets from the NDSC (Network for Detection of Stratospheric Change) stations of Harestua (60° N, 10° E) and Andøya (69° N, 16° E) in Norway. The information content and retrieval errors have been analyzed following a formalism used for characterizing ozone profiles retrieved from solar infrared absorption spectra. In order to validate the technique, the retrieved NO2 vertical profiles and columns have been compared to correlative balloon and satellite observations. Such extensive validation of the profile and column retrievals was not reported in previously published work on the profiling from GB UV-visible measurements. A good agreement - generally better than 25% - has been found with the SAOZ (Système d'Analyse par Observations Zénithales) and DOAS (Differential Optical Absorption Spectroscopy) balloons. A similar agreement has been reached with correlative satellite data from the HALogen Occultation Experiment (HALOE) and Polar Ozone and Aerosol Measurement (POAM) III instruments above 25km of altitude. Below 25km, a systematic underestimation - by up to 40% in some cases - of both HALOE and POAM III profiles by our GB profile retrievals has been observed, pointing out more likely a limitation of both satellite instruments at these altitudes. We have concluded that our study strengthens our confidence in the reliability of the retrieval of vertical distribution information from GB UV-visible observations and offers new perspectives in the use of GB UV-visible network data for validation purposes.

Antarctic stratospheric ozone from the assimilation of occultation data

Ozone data from the solar occultation Polar Ozone and Aerosol Measurement (POAM) III instrument are included in the ozone assimilation system at NASA's Global Modeling and Assimilation Office, which uses Solar Backscatter UltraViolet/2 (SBUV/2) instrument data. Even though POAM data are available at only one latitude in the southern hemisphere on each day, their assimilation leads to more realistic ozone distribution throughout the Antarctic region, especially inside the polar vortex. Impacts of POAM data were evaluated by individual and statistical comparisons of assimilated ozone profiles with independent ozone sondes. Major improvements in ozone representation are seen in the Antarctic lower stratosphere during austral winter and spring in 1998. Limitations of assimilation of sparse occultation data are illustrated by an example.

Interannual Changes of Stratospheric Water Vapor and Correlations with Tropical Tropopause Temperatures

Interannual variations of stratospheric water vapor over 1992‐2003 are studied using Halogen Occultation Experiment (HALOE) satellite measurements. Interannual anomalies in water vapor with an approximate 2-yr periodicity are evident near the tropical tropopause, and these propagate vertically and latitudinally with the mean stratospheric transport circulation (in a manner analogous to the seasonal ‘‘tape recorder’’). Unusually low water vapor anomalies are observed in the lower stratosphere for 2001‐03. These interannual anomalies are also observed in Arctic lower-stratospheric water vapor measurements by the Polar Ozone and Aerosol Measurement (POAM) satellite instrument during 1998‐2003. Comparisons of the HALOE data with balloon measurements of lower-stratospheric water vapor at Boulder, Colorado (408N), show partial agreement for seasonal and interannual changes during 1992‐2002, but decadal increases observed in the balloon measurements for this period are not observed in HALOE data. Interannual changes in HALOE water vapor are well correlated with anomalies in tropical tropopause temperatures. The approximate 2-yr periodicity is attributable to tropopause

High-Frequency Planetary Waves in the Polar Middle Atmosphere as Seen in a Data Assimilation System

This study examines the winter southern hemisphere vortex of 1998 using four times daily output from a data assimilation system to focus on the polar 2-day, wave number 2 component of the 4-day wave. The data assimilation system products are from a test version of the finite volume data assimilation system (fvDAS) being developed at Goddard Space Flight Center (GSFC) and include an ozone assimilation system. Results show that the polar 2-day wave dominates during July 1998 at 70 degrees. The period of the quasi 2-day wave is somewhat shorter than 2 days (about 1.7 days) during July 1998 with an average perturbation temperature amplitude for the month of over 2.5 K. The 2-day wave propagates more slowly than the zonal mean zonal wind, consistent with Rossby wave theory, and has EP flux divergence regions associated with regions of negative horizontal potential vorticity gradients, as expected from linear instability theory. Results for the assimilation-produced ozone mixing ratio show that the 2-day wave represents a major source of ozone variation in this region. The ozone wave in the assimilation system is in good agreement with the wave seen in the POAM (Polar Ozone and Aerosol Measurement) ozone observations for the same time period. Some differences with linear instability theory are noted as well as spectral peaks in the ozone field, not seen in the temperature field, that may be a consequence of advection.

Antarctic air over New Zealand following vortex breakdown in 1998

Abstract. An ozonesonde profile over the Network for Detection of Stratospheric Change (NDSC) site at Lauder (45.0° S, 169.7° E), New Zealand, for 24 December 1998 showed atypically low ozone centered around 24 km altitude (600 K potential temperature). The origin of the anomaly is explained using reverse domain filling (RDF) calculations combined with a PV/O3 fitting technique applied to ozone measurements from the Polar Ozone and Aerosol Measurement (POAM) III instrument. The RDF calculations for two isentropic surfaces, 550 and 600 K, show that ozone-poor air from the Antarctic polar vortex reached New Zealand on 24–26 December 1998. The vortex air on the 550 K isentrope originated in the ozone hole region, unlike the air on 600 K where low ozone values were caused by dynamical effects. High-resolution ozone maps were generated, and their examination shows that a vortex remnant situated above New Zealand was the cause of the altered ozone profile on 24 December. The maps also illustrate mixing of the vortex filaments into southern midlatitudes, whereby the overall mid-latitude ozone levels were decreased.Key words. Atmospheric composition and structure (middle atmosphere composition and chemistry) – Meteorology and atmospheric dynamics (middle atmosphere dynamics)

Validation of POAM III ozone: Comparisons with ozonesonde and satellite data

This paper describes the validation of ozone profiles from the Polar Ozone and Aerosol Measurement (POAM) III instrument. POAM III O3 is measured with 1‐km vertical resolution throughout most of the stratosphere and random errors of ∼5%. It is shown that sunspots do not significantly affect the POAM O3 retrievals, nor do polar stratospheric clouds, except under rarely encountered, extreme conditions of very low O3 and exceptionally high aerosol extinction. A statistical analysis is presented of comparisons between coincident measurements from POAM III and ozonesondes, the Halogen Occultation Experiment (HALOE) and the Stratospheric Aerosol and Gas Experiment (SAGE) II. On average, POAM III O3 profiles agree to within ±5% with these correlative data from 13 to 60 km. There is a suggestion that from 30 to 60 km POAM III sunrise data might be biased slightly low (<5%) relative to POAM sunset data. There is evidence that POAM III has a high bias of up to ∼0.1 ppmv from 10 to 12 km, and that this bias might stem, in part, from errors in the retrieval of aerosol extinction at 0.6 μm, the primary O3 absorption wavelength in the POAM retrievals. Below 10 km the POAM III data agree with coincident sonde measurements to better than 0.05 ppmv on average, which can correspond to large relative differences of more than +30% at 8–9 km and −100% at 5 km. We conclude that the POAM III profiles are highly accurate and adequate for quantitative scientific studies.