Ozone Profile Data Research Articles

The 10-day planetary wave examined by Odin/OSIRIS ozone profiles during late March 2002: comparison with UKMO and MF radar data

Ozone profile data have been retrieved from the Optical Spectrograph and InfraRed Imager System (OSIRIS) instrument onboard the Odin Satellite, which was launched on 20 February 2001. Considering the irregular sampling of the OSIRIS, a least-squares fit method is employed to provide the wavenumber and frequency spectra of the waves affecting the OSIRIS ozone profile distributions. Meanwhile, criteria are developed and applied for reducing spectral biases. Then spectral analysis of the global OSIRIS ozone profiles data is perfomred at altitudes of 38.5 km and 40.5 km within two latitude bins 35˚–45˚N and 45˚–55˚N during days 75–105 of the year 2002. Specifically, a westward-propagating 10-day planetary wave is detected and validated by medium frequency (MF) Radar (MFR) at Platteville (40˚N, 105˚W) and Saskatoon (52˚N, 107˚W), and UKMO global stratospheric data (UK Meteorological Office assimilated model). The spatial and temporal distributions of the global OSIRIS ozone profile data are shown to allow identification of major planetary wave features in the middle atmosphere.

A long‐term stratospheric ozone data set from assimilation of satellite observations: High‐latitude ozone anomalies

A 29 year data set of stratospheric ozone from sequential assimilation of solar backscatter UV (SBUV) satellite ozone profile observations into a chemical transport model is introduced and validated against independent observations (satellite instruments and sondes). Our assimilated data set shows excellent agreement with ozone profile data from sonde measurements from high‐latitude observation sites on both hemispheres and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite observations, including during polar night when no SBUV observations are available. Although we only assimilate ozone profiles, total column ozone in the assimilated data set is in good agreement with independent satellite observations from the Global Ozone Monitoring Experiment (GOME), the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY), and the Total Ozone Mapping Spectrometer (TOMS). The data set can thus be viewed as a consistent long‐term data set closing the gaps in satellite observations in order to investigate high‐latitude ozone variability. We then use the assimilated data set to analyze the development and persistence of both high and low ozone anomalies in the Arctic stratosphere. Ozone anomalies typically develop in the 1000 K potential temperature (∼35 km) region and slowly descend from there, remaining visible for around 7 months. Anomalies in the stratospheric circulation, expressed by the Northern Hemisphere annular mode (NAM) index, show a large influence on ozone anomalies. Extreme phases of the NAM index (strong and weak vortex events) lead to the creation of distinctively shaped ozone anomalies, which first appear in the uppermost stratosphere and then rapidly cover the upper and middle stratosphere, from where they then slowly descend into the lowermost stratosphere within 5 months.

Modulations of the 27 day solar rotation signal in stratospheric ozone from Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) (2003–2008)

Here we investigate the modulating nature of the 27 day solar rotation forcing on stratospheric ozone using a new ozone profile data set from Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY, 2003–2008). Continuous wavelet transform (CWT), fast Fourier transform (FFT), and cross correlations (CC) have been applied to SCIAMACHY ozone in the tropics (<20° latitude) between 20 and 60 km altitude. The maximum correlation between Mg II index and ozone is weaker during the maximum of solar cycle 23 (r = 0.38) than in the previous two solar cycles that have been investigated in earlier studies using different data sets. The magnitude of the ozone signal is highly time dependent and may vanish for several solar rotations even close to solar maximum conditions. The FFT analysis reveals, besides the 27 day signal, several frequencies close to 27 days. The ozone sensitivity (ozone change in percent per percent change in 205 nm solar flux) is on average about 0.2%/% above 30 km altitude and smaller by about a factor of 2 compared to earlier studies. For selected 3 month periods the sensitivity may rise beyond 0.6%/% in better agreement with earlier studies. The analysis of the 27 day solar forcing was also carried out with stratospheric temperatures from European Centre for Medium‐Range Weather Forecasts operational analysis. Although direct radiation effects on temperature are weak in the upper stratosphere, temperature signals with statistically significant periods in the 25–35 day range similar to ozone could be found with the applied methods.

Features of ozone mini-hole events over the Tibetan Plateau

Based on TOMS total ozone data and SCIAMACHY ozone profile data, climatology of the ozone mini-hole events over the Tibetan Plateau and ozone vertical structure variations during an ozone mini-hole event in December 2003 are analyzed. The analyses show that before 1990 ozone mini-hole events only occurred in November–December of 1987 but that the number of events increases after 1990. These events only occur from October through February, with maximum occurrence frequency in December. During the event in December 2003, the decrease in total ozone of over 20% is mainly caused by the ozone loss in the upper troposphere and lower stratosphere region due to the horizontal transport of low ozone from the lower latitude subtropics and the uplift of low ozone from the lower troposphere over the Tibetan Plateau.

Intercomparison of ozone profile measurements from ASUR, SCIAMACHY, MIPAS, OSIRIS, and SMR

The airborne submillimeter radiometer (ASUR) was deployed onboard the Falcon research aircraft during the scanning imaging absorption spectrometer for atmospheric cartography (SCIAMACHY) validation and utilization experiment (SCIAVALUE) and the European polar stratospheric cloud and lee wave experiment (EuPLEx) campaigns. A large number of ozone profile measurements were performed over a latitude band spanning from 5°S to 80°N in September 2002 and February/March 2003 during the SCIAVALUE and around the northern polar latitudes in January/February 2003 during the EuPLEx. Both missions amassed an ample microwave ozone profile data set that is used to make quantitative comparisons with satellite measurements in order to assess the quality of the satellite retrievals. In this paper, the ASUR ozone profile measurements are compared with measurements from SCIAMACHY and Michelson interferometer for passive atmospheric sounding (MIPAS) on Environmental Satellite and optical spectrograph and infrared imager system (OSIRIS) and submillimeter radiometer (SMR) on the Odin satellite. The cross comparisons with the criterion that the ASUR measurements are performed within ±1000 km and ±6 hrs of the satellite observations show a good agreement with all the four satellite sensors. The differences in data values are the following: −4 to +8% for ASUR‐SCIAMACHY (operational product, v2.1), within ±15% for ASUR‐SCIAMACHY (scientific product, v1.62), up to +6% for ASUR‐MIPAS (operational product v4.61) and ASUR‐MIPAS (scientific product v1‐O3‐1), up to 17% for ASUR‐OSIRIS (v012), and −6 to 17% for ASUR‐SMR (v222) between the 20‐ and 40‐km altitude range depending on latitude. Thus, the intercomparisons provide important quantitative information about the quality of the satellite ozone profiles, which has to be considered when using the data for scientific analyses.

A stratospheric ozone profile data set for 1979–2005: Variability, trends, and comparisons with column ozone data

A global stratospheric ozone data set for 1979–2005 is described. Interannual variations are derived from analysis of Stratospheric Aerosol and Gas Experiment (SAGE I and II) profile measurements, combined with polar ozonesonde data from Syowa (69°S) and Resolute (75°N). These interannual changes are combined with a seasonally varying ozone climatology from Fortuin and Kelder [1998] to provide a monthly global data set. These data are intended for use in global modeling studies and for analysis of global variability and trends. In order to generate continuous fields from the gappy SAGE data, we use a regression fit that includes decadal trends, solar cycle, and QBO terms, and the spatial structure of these variations is studied in detail. Decadal trends are modeled using an equivalent effective stratospheric chlorine proxy. Ozone variability from the vertically integrated SAGE/sonde data set is compared with results derived from a merged Total Ozone Mapping Spectrometer/solar backscatter ultraviolet column ozone data set, showing good overall agreement (in particular for trends in extratropics). We also compare the SAGE data with ozonesonde measurements over Northern Hemisphere midlatitudes and find excellent agreement for lower stratospheric variability and trends. In the tropics, the SAGE ozone data show relatively large percentage decreases in the lower stratosphere. However, the vertically integrated SAGE data do not agree with column ozone trends in the tropics, so there is less confidence in the SAGE results in this region.

Solar cycle variation of stratospheric ozone: Multiple regression analysis of long‐term satellite data sets and comparisons with models

Previous multiple regression analyses of the solar cycle variation of stratospheric ozone are improved by (1) analyzing three independent satellite ozone data sets with lengths extending up to 25 years and (2) comparing column ozone measurements with ozone profile data during the 1992–2003 period when no major volcanic eruptions occurred. Results show that the vertical structure of the tropical ozone solar cycle response has been consistently characterized by statistically significant positive responses in the upper and lower stratosphere and by statistically insignificant responses in the middle stratosphere (∼28–38 km altitude). This vertical structure differs from that predicted by most models. The similar vertical structure in the tropics obtained for separate time intervals (with minimum response invariably near 10 hPa) is difficult to explain by random interference from the QBO and volcanic eruptions in the statistical analysis. The observed increase in tropical total column ozone approaching the cycle 23 maximum during the late 1990s occurred primarily in the lower stratosphere below the 30 hPa level. A mainly dynamical origin for the solar cycle total ozone variation at low latitudes is therefore likely. The amplitude of the solar cycle ozone variation in the tropical upper stratosphere derived here is somewhat reduced in comparison to earlier results. Additional data are needed to determine whether this upper stratospheric response is or is not larger than model estimates.

Geophysical validation of SCIAMACHY Limb Ozone Profiles

Abstract. We discuss the quality of the two available SCIAMACHY limb ozone profile products. They were retrieved with the University of Bremen IFE's algorithm version 1.61 (hereafter IFE), and the official ESA offline algorithm (hereafter OL) versions 2.4 and 2.5. The ozone profiles were compared to a suite of correlative measurements from ground-based lidar and microwave, sondes, SAGE II and SAGE III (Stratospheric Aerosol and Gas Experiment). To correct for the expected Envisat pointing errors, which have not been corrected implicitly in either of the algorithms, we applied a constant altitude shift of -1.5 km to the SCIAMACHY ozone profiles. The IFE ozone profile data between 16 and 40 km are biased low by 3-6%. The average difference profiles have a typical standard deviation of 10% between 20 and 35 km. We show that more than 20% of the SCIAMACHY official ESA offline (OL) ozone profiles version 2.4 and 2.5 have unrealistic ozone values, most of these are north of 15° S. The remaining OL profiles compare well to correlative instruments above 24 km. Between 20 and 24 km, they underestimate ozone by 15±5%.

An Estimate of the Vertical Ozone Profile Discrepancy between the Australian Brewer–Mast and Electrochemical Concentration Cell Ozonesondes

Abstract An analysis is described that provides an additive correction for referencing the vertical ozone profiles of the Australian Brewer–Mast (BM; October 1984–December 1990) ozonesonde to those of the electrochemical concentration cell (ECC; January 1991–December 1999) using approximately coincident Stratospheric Aerosol and Gas Experiment (SAGE) II satellite ozone profile data. Because Australian BM ozonesondes may have been prepared differently from BM ozonesondes elsewhere, other results of intercomparisons between the two different ozonesonde types cannot be used. However, the present results are consistent with previously reported intercomparison studies between these two ozonesonde types, where the lowest altitude tropospheric ozone levels measured by the BM ozonesonde were approximately 25% lower than the values measured by the ECC ozonesonde. The magnitudes of the BM corrections were found to be generally less than about 0.5 mPa in partial pressure up to an altitude of approximately 28 km. Without direct intercomparison measurements, the corrections given here provide the only means of removing the discontinuity in the Melbourne ozonesonde dataset that occurred when ECC ozonesondes replaced the BM ozonesondes in 1991.

Equatorial Kelvin wave signatures in ozone profile measurements from Global Ozone Monitoring Experiment (GOME)

This study investigates the ability to derive height‐resolved information on equatorial Kelvin wave activity from three different Global Ozone Monitoring Experiment (GOME) ozone profile data sets. The ozone profiles derived using the Ozone Profile Retrieval Algorithm (OPERA) based on optimal estimation and the Neural Network Ozone Retrieval System (NNORSY) both show Kelvin wave signals in agreement with previously identified signals in the GOME total ozone columns. However, because of the inadequate vertical resolution, these two data sets are not able to resolve the vertical structure of the Kelvin wave activity. The third data set, consisting of assimilated OPERA ozone profiles, does provide height‐resolved information on Kelvin wave activity that is consistent with results from the analysis of GOME total ozone columns and ECMWF Re‐Analysis (ERA‐40) temperature data. Largest Kelvin‐wave‐induced perturbations of up to 0.69 DU/km coincide with the maximum vertical gradient in ozone around 35 hPa and show an in‐phase relationship with temperature perturbations in ERA‐40 as expected from theoretical considerations. These results indicate that the ozone perturbations in the lower stratosphere and in the total column of ozone are transport related. Between 10 and 1 hPa, large Kelvin‐wave‐induced fluctuations in ozone mixing ratio are present that, however, because of their small contribution to the total column, do not constitute a large contribution to the total ozone column perturbations. The ozone perturbations between 10 and 1 hPa show an out‐of‐phase relationship with temperature perturbations in ERA‐40, indicating that the perturbations can either be caused by transport effects or photochemical influences.

Aspects of ozone transport, mixing, and chemistry in the greater Maryland area

This study examined the role of ozone transported and the subsequent mixing of the transported ozone on the ozone concentration and chemistry in the surface layer at locations in central Maryland. Surface data from the United States Environmental Protection Agency's (EPA) Aerometric Information Retrieval System (AIRS) database, ozone profile data from the University of Maryland's aircraft measurements, trajectory analyses using the HYSPLIT model, and predictions using the Semi-Empirical Integrated Pollution Model (SIPM) for the periods 11–15 July 1995 and 12–16 July 1997 were used to meet the objectives of this study. It was found that on the day before the air mass reached the receptor in Maryland, the air mass passed over regions where the diurnal maximum ozone concentration was sufficiently large and the mixing sufficiently deep, in most cases, to have been the primary source of the ozone that was found over central Maryland the next morning. Mixing took place between the air mass above the nocturnal inversion and the surface layer when the nocturnal inversion broke down sometime after sunrise, and the ozone in the surface layer increased by about 13 ppb, on average, as a result of the mixing. The results also showed that when certain conditions were met, the chemistry in the surface layer produced up to about three times more ozone when mixing of ozone into the surface layer took place and when a non-zero value for the diurnal minimum zone concentrations were used to initialize the chemistry. There were, however, a number of situations when mixing of ozone into the surface layer and when a non-zero value for the diurnal minimum ozone concentrations were used to initialize the chemistry, had little effect on the surface ozone layer. The conditions, under which both situations occurred, are discussed.

Ozone column classified climatology of ozone and temperature profiles based on ozonesonde and satellite data

An updated and atmospheric dynamics oriented global climatology of ozone profiles has been derived from ozonesonde and satellite observations. The climatology, which uses total ozone to parameterize the profile shape, provides improved a priori information for ozone profile retrieval from satellite measurements using optimal estimation. It can be also used to correct the profile shape error in total ozone retrieval. Sonde data were selected from the 1990–2000 and 1988–1999 period for SAGE II excluding two years of SAGE II V6.1 data influenced by the Mount Pinatubo eruption in 1991. In addition, POAM III V3 data covering the polar region and SHADOZ ozonesonde data in the tropics were included. The ozone profile data were binned in steps of 30 DU of total ozone, 30° wide zonal bands, and into a six‐month season (winter/spring and summer/fall) in middle and high latitudes. No seasonal distinction is needed in the low‐latitude region (30°S to 30°N). Mean and standard deviation profiles for each ozone class were combined from satellites and sondes with a transition region in the range 20–26 km to merge both data sets. Temperature data from sonde, SAGE II collocated NMC, and POAM III collocated UKMO, where NMC and UKMO data are used in respective ozone retrieval, have been binned and averaged in the same manner as the ozone profiles so that for each mean ozone profile a matching temperature profile was derived. Corresponding ozone and temperature profiles help in accounting for the temperature dependence of the ozone absorption cross sections in the retrieval process. Key features of both ozone and temperature climatologies are discussed. As examples, ozone‐temperature correlation and the climatology of tropopause heights as derived from this climatology are presented, and they serve as diagnostic tools to show that the new climatology is a representative data set for global applications. Good agreement between collocated sonde profiles from Hohenpeissenberg (47.8°, 11.0°) and GOME ozone profiles, retrieved using optimal estimation method and using this climatology as constraints, was found. Also, comparison with GOME results, which were retrieved using a zonal monthly mean climatology, demonstrates the large improvements achieved by using this new climatology, particularly in the lowermost stratosphere and tropopause region.

SHADOZ—A TROPICAL OZONESONDE–RADIOSONDE NETWORK FOR THE ATMOSPHERIC COMMUNITY

This article describes the Southern Hemisphere Additional Ozonesondes (SHADOZ) network of ozonesonde-radiosonde stations in the southern Tropics and subtropics. SHADOZ was initiated in 1998 by NASA, NOAA, and a team of international meteorological services and space agencies to remedy a paucity of ozone profile data in a region of intense natural variability and anthropogenic change. SHADOZ augments launches at selected sites and provides a public archive of ozonesonde and radiosonde data (see additional information online at http://croc.gsfc.nasa.gov/shadoz). Ozone is important because of its role as an atmospheric UV shield, surface pollutant, oxidant, and greenhouse gas. Ozone profile data are essential for the detection of ozone trends and for verification of satellite ozone retrievals. Instrumentation, data, and a summary of the first scientific findings from SHADOZ are presented. A zonal view shows that troposphere ozone accumulates over the south tropical Atlantic and adjacent continents throughout...

Tropospheric ozone over the North Pacific from ozonesonde observations

As part of the Transport and Chemical Evolution over the Pacific (TRACE‐P) mission, ozonesondes were used to make ozone vertical profile measurements at nine locations in the North Pacific. At most of the sites there is a multiyear record of observations. From locations in the western Pacific (Hong Kong; Taipei; Jeju Island, Korea; and Naha, Kagoshima, Tsukuba, and Sapporo, Japan), a site in the central Pacific (Hilo, Hawaii), and a site on the west coast of the United States (Trinidad Head, California) both a seasonal and event specific picture of tropospheric ozone over the North Pacific emerges. Ozone profiles over the North Pacific generally show a prominent spring maximum throughout the troposphere. This maximum is tied to the location of the jet stream and its influence on stratosphere‐troposphere exchange and the increase in photochemical ozone production through the spring. Prominent layers of enhanced ozone in the middle and upper troposphere north of about 30°N seem to be more closely tied to stratospheric intrusions while biomass burning leads to layers of enhanced ozone in the lower and upper troposphere at Hong Kong (22°N) and Taipei (25°N). The lower free tropospheric layers at Hong Kong are associated with burning in SE Asia, but the upper layer may be associated with either equatorial Northern Hemisphere burning in Africa or SE Asian biomass burning. In the boundary layer at Taipei very high mixing ratios of ozone were observed that result from pollution transport from China in the spring and local urban pollution during the summer. At the ozonesonde site near Tokyo (Tsukuba, 36°N) very large enhancements of ozone are seen in the boundary layer in the summer that are characteristic of urban air pollution. At sites in the mid and eastern Pacific the signature of transport of polluted air from Asia is not readily identifiable from the ozonesonde profile. This is likely due to the more subtle signal and the fact that from the ozone profile and meteorological data by themselves it is difficult to identify such a signal. During the TRACE‐P intensive campaign period (February–April 2001), tropospheric ozone amounts were generally typical of those seen in the long‐term records of the stations with multiyear soundings. The exception was the upper troposphere over Hong Kong and Taipei where ozone amounts were lower in 2001.

Stratospheric ozone loss in the 1996/1997 Arctic winter: Evaluation based on multiple trajectory analysis for double‐sounded air parcels by ILAS

Quantitative chemical ozone loss rates and amounts in the Arctic polar vortex for the spring of 1997 are analyzed based on ozone profile data obtained by the Improved Limb Atmospheric Spectrometer (ILAS) using an extension of the Match technique. In this study, we calculated additional multiple trajectories and set very strict criteria to overcome the weakness of the satellite sensor data (lower vertical resolution and larger sampling air mass volume) and to identify more accurately a double‐sounded air mass. On the average inside the inner edge of the vortex boundary (north of about 70°N equivalent latitude), the local ozone loss rate was 50–80 ppbv/day at the maximum during late February between the levels of 450 and 500 K potential temperatures. The integrated ozone loss during February to March reached 2.0 ± 0.1 ppmv at 475–529 K levels, and the column ozone loss between 400 and 600 K during the 2 months was 96 ± 0.3 DU. Using a relative potential vorticity (rPV) scale, the vortex was divided into some rPV belts, and it was shown that the magnitude of the ozone loss increased gradually toward the vortex center from the edge. The maximum ozone loss rate of 6.0 ± 0.6 ppbv/sunlit hour near the vortex center was higher than near the vortex edge by a factor of 2–3. When we expanded the area of interest to include all the data obtained inside the vortex edge (north of about 65°N equivalent latitude), the local ozone loss rate was about 50 ppbv/day at the maximum. This value is slightly larger than that estimated by the Match analysis using ozonesondes for the same winter by ∼10 ppbv/day. Temperature histories of double‐sounded air parcels indicated that the extreme ozone loss in the innermost part of the vortex was observed when the air parcel experienced temperatures below TNAT during the two soundings and had experienced temperatures near Tice in the 10 days prior to the first sounding. These facts suggest that the high ozone loss rate deep inside the vortex in the 1997 Arctic early spring correlates with the presence of type Ia polar stratospheric clouds (PSCs).

On shifts in the long‐term Umkehr radiance records and their influence on retrieved ozone profiles

The Umkehr technique has been used routinely for more than 40 years to assess features in the vertical distribution of ozone. The measurements represent the longest ozone profile data record in existence. A careful examination of the long‐term Umkehr N‐value (radiance) measurement record, archived at the WMO World Ozone and UV Data Center in Toronto, Canada, revealed shifts in the data. These shifts appear to be mainly related to Dobson instrument calibrations and/or to instrument changes at the observing stations. In most cases, the detected shifts exhibit solar zenith angle dependence. The standard procedure of subtracting the Umkehr measurement at 60‐degree solar zenith angle (or the next smallest SZA available) from the measurement at the other angles to eliminate the instrumental and extraterrestrial constants from measurements does not necessarily remove the shifts. The shift errors would appear as shifts in the retrieved ozone profiles and could affect any ozone profile analysis (including ozone trends) as well as comparisons with other profiles derived from satellite and lidar measurements. A preliminary approach for detecting the shifts and allowing for corrections is developed and evaluated for its potential to improve the quality of the of the Umkehr records.

Ozone changes in the lower stratosphere from the Halogen Occultation Experiment for 1991 through 1999

The Upper Atmospheric Research Satellite (UARS) Halogen Occultation Experiment (HALOE) Version 19 ozone profile data set was analyzed for both periodic and nonseasonal polynomial changes in lower stratospheric ozone for 1991–1999. The profile data were screened for cloud contamination at the lowest levels and were then integrated within six half‐Umkehr (each ∼2.5 km thick) layers from 32 to 253 hPa. The column values were then binned and averaged into 10°‐wide latitude regions but separated into sunrise and sunset measurements, yielding an effective time series of zonal‐averaged ozone that spans 8 years. The results extend to near tropopause levels, 253 hPa in the extratropics and 127 hPa in the tropics. Multiple linear regression techniques were applied to the data of each latitude zone and half‐Umkehr layer. We developed models that included annual, semiannual, and interannual periodic terms plus polynomial terms at 50°N, 30°N, equator, 30°S, and 50°S. The amplitudes of the three periodic terms vary with latitude and pressure altitude and do not maintain their same order of importance in all cases, emphasizing the changes and hemispheric asymmetry of the transport mechanisms in the lower stratosphere. We find no clear evidence for long‐term change at most latitudes and layers. Steady declines in ozone of 0.5% yr−1 were found in the 32–45 hPa layer at 50°S, most likely due to transport of ozone‐depleted air from higher latitudes. Our lowest tropical layer (90–127 hPa) shows an ozone decline in the early 1990s but an increase in the last half of the decade. Steady increases of ozone of 3–4% yr−1 were found at 50°N from 127 to 253 hPa and at 30°N from 179 to 253 hPa, probably in response to a changing net circulation for the Northern Hemisphere lower stratosphere. However, there is no highly significant trend at 50°N for the column ozone over the deeper layer from 8 to 253 hPa. For Northern Hemisphere middle latitudes it is concluded that the previously reported declines of zonal‐average ozone in the lower stratosphere for the 1980s and early 1990s have not continued over the decade of the 1990s.

ILAS observations of chemical ozone loss in the Arctic vortex during early spring 1997

Chemical ozone loss rates were estimated for the Arctic stratospheric vortex by using ozone profile data (Version 3.10) obtained with the Improved Limb Atmospheric Spectrometer (ILAS) for the spring of 1997. The analysis method is similar to the Match technique, in which an air parcel that the ILAS sounded twice at different locations and at different times was searched from the ILAS data set, and an ozone change rate was calculated from the two profiles. A statistical analysis indicates that the maximum ozone loss rate was found on the 450 K potential temperature surface in February, amounting to 84 ppbv/day. The integrated ozone loss for two months from February to March 1997 showed its maximum of 1.5±0.1 ppmv at the surface that followed the diabatic descent of the air parcels and reached the 425 K level on March 31. This is about 50% of the initial (February 1) ozone concentration. The present study demonstrated that data from a solar occultation sensor with a moderate altitude resolution can be used for the Match analysis.

Update of Umkehr ozone profile data trend analysis through 1997

An extended update of both nonseasonal and seasonal trend analysis for northern hemisphere Umkehr ozone profile data from 1977 through 1997 is presented. The nonseasonal or year‐round trend analysis reaffirms the previous results of significant negative ozone trend in the upper stratospheric Umkehr layers 7, 8, and 8–10 (33–48 km) of about −0.5% per year, with little trend in the middle stratospheric layer 5 (24–28 km). In addition, the Umkehr data show a substantial negative trend in the lower stratospheric Umkehr layer 2–3 (10–19 km) of about −0.4% per year. Two procedures for the correction of the Umkehr measurements for errors due to volcanic aerosols are considered, and trend results are quite similar using both aerosol‐correction procedures. With respect to the seasonal trend aspects, the analysis indicates relatively small trend differences over seasons in the upper layers, where trends in the winter and spring seasons are only slightly more negative than those in the summer and fall seasons, by about −0.1% per year. In the lower stratospheric layer 2–3, however, a strong seasonal pattern in trends is observed in the midlatitude Umkehr data, with the most extreme negative trends, of about −0.6% per year, occurring in the spring and winter, the least negative trends, of about −0.2% per year, occurring in the fall, and the summer trends of about −0.4% per year are intermediate. Also, the trends in layer 2–3 are substantially more negative for the higher latitude range of 40–52°N than for the lower latitude range of 26–39°N, by about −0.3% per year during all seasons, with even larger differences in the spring.

Tropospheric ozone above the southwestern Indian Ocean is strongly linked to dynamical conditions prevailing in the tropics

A large ozone profile data set obtained at Réunion Island (21°S, 55°E) since 1992 is presented and linked to observed dynamical conditions in the region. The average seasonal variation of column integrated tropospheric ozone reaches 25 Dobson Units and peaks at 55 Dobson Units during the month of October. Two thermal inversions and high values of ozone mixing ratio during biomass burning activity in southeastern Africa are observed. The marine boundary layer (MBL) is characterized by high relative humidity values and low ozone mixing ratios. The decrease in the water vapor content above 2 km is strongly linked to seasonally evolving dynamical conditions. The first inversion largely hinders vertical exchanges, and low water vapor values in the free troposphere favor the photochemical production of ozone. The second thermal inversion is linked to the zonal wind inversion. Above this second inversion a large ozone enhancement is observed that occurs in parallel the biomass‐burning season in southeastern Africa and Madagascar. The season extents from August to December and peaks in October. The ozone maximum concomitantly results from the transport of ozone and its precursors westward from the biomass‐burning zones. High ozone values recorded in the upper troposphere during austral winter are likely to originate from additional stratosphere‐troposphere exchanges. Winter anticyclonic conditions further favor the photochemical production of ozone. The low tropospheric ozone mixing ratios observed across the entire troposphere during austral summer could result from the heterogeneous destruction of ozone and from less favorable conditions for its photochemical production, because of the development of deep convection.