Umkehr Measurements Research Articles

Optimized Umkehr profile algorithm for ozone trend analyses

Abstract. The long-term record of Umkehr measurements from four NOAA Dobson spectrophotometers was reprocessed after updates to the instrument calibration procedures. In addition, a new data quality-control tool was developed for the Dobson automation software (WinDobson). This paper presents a comparison of Dobson Umkehr ozone profiles from NOAA ozone network stations – Boulder, the Haute-Provence Observatory (OHP), the Mauna Loa Observatory (MLO), Lauder – against several satellite records, including Aura Microwave Limb Sounder (MLS; ver. 4.2), and combined solar backscatter ultraviolet (SBUV) and Ozone Mapping and Profiler Suite (OMPS) records (NASA aggregated and NOAA cohesive datasets). A subset of satellite data is selected to match Dobson Umkehr observations at each station spatially (distance less than 200 km) and temporally (within 24 h). Umkehr Averaging kernels (AKs) are applied to vertically smooth all overpass satellite profiles prior to comparisons. The station Umkehr record consists of several instrumental records, which have different optical characterizations, and thus instrument-specific stray light contributes to the data processing errors and creates step changes in the record. This work evaluates the overall quality of Umkehr long-term measurements at NOAA ground-based stations and assesses the impact of the instrumental changes on the stability of the Umkehr ozone profile record. This paper describes a method designed to correct biases and discontinuities in the retrieved Umkehr profile that originate from the Dobson calibration process, repair, or optical realignment of the instrument. The Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) Global Modeling Initiative (M2GMI) and NASA Global Modeling Initiative chemistry transport model (GMI CTM) ozone profile model output matched to station location and date of observation is used to evaluate instrumental step changes in the Umkehr record. Homogenization of the Umkehr record and discussion of the apparent stray light error in retrieved ozone profiles are the focus of this paper. Homogenization of ground-based records is of great importance for studies of long-term ozone trends and climate change.

A fully automated Dobson sun spectrophotometer for total column ozone and Umkehr measurements

Abstract. The longest ozone column measurement series are based on the Dobson sun spectrophotometers developed in the 1920s by Prof. G. B. W. Dobson​​​​​​​. These ingenious and robustly designed instruments still constitute an important part of the global network presently. However, the Dobson sun spectrophotometer requires manual operation, which has led to the discontinuation of its use at many stations, thus disrupting long-term records of observation. To overcome this problem, MeteoSwiss developed a fully automated version of the Dobson spectrophotometer. The description of the data acquisition and automated control of the instrument is presented here with some technical details. The results of different tests performed regularly to assess the instrument's good working conditions are illustrated and discussed. Compared to manual operation, automation results in a higher number of daily measurements with lower random error and additional housekeeping information to characterize the measuring conditions. The automated Dobson instrument allows for continuous observation of the ozone column with a resolution of ∼ 1 DU under clear-sky conditions.

A new Dobson Umkehr ozone profile retrieval method optimising information content and resolution

Abstract. The standard Dobson Umkehr methodology to retrieve coarse-resolution ozone profiles used by the National Oceanographic and Atmospheric Administration uses designated solar zenith angles (SZAs). However, some information may be lost if measurements lie outside the designated SZA range (between 60° and 90°), or do not conform to the fitting technique. Also, while Umkehr measurements can be taken using multiple wavelength pairs (A, C and D), past retrieval methods have focused on a single pair (C). Here we present an Umkehr inversion method that uses measurements at all SZAs (termed operational) and all wavelength pairs. (Although, we caution direct comparison to other algorithms.) Information content for a Melbourne, Australia (38° S, 145° E) Umkehr measurement case study from 28 January 1994, with SZA range similar to that designated in previous algorithms is shown. When comparing the typical single wavelength pair with designated SZAs to the operational measurements, the total degrees of freedom (independent pieces of information) increases from 3.1 to 3.4, with the majority of the information gain originating from Umkehr layers 2 + 3 and 4 (10–20 km and 25–30 km respectively). In addition to this, using all available wavelength pairs increases the total degrees of freedom to 5.2, with the most significant increases in Umkehr layers 2 + 3 to 7 and 9+ (10–40 and 45–80 km). Investigating a case from 13 April 1970 where the measurements extend beyond the 90° SZA range gives further information gain, with total degrees of freedom extending to 6.5. Similar increases are seen in the information content. Comparing the retrieved Melbourne Umkehr time series with ozonesondes shows excellent agreement in layers 2 + 3 and 4 (10–20 and 25–30 km) for both C and A + C + D-pairs. Retrievals in layers 5 and 6 (25–30 and 30–35 km) consistently show lower ozone partial column compared to ozonesondes. This is likely due to stray light effects that are not accounted for in the forward model, and under represented stratospheric aerosol.

Validation of MIPAS IMK/IAA V5R_O3_224 ozone profiles

Abstract. We present the results of an extensive validation program of the most recent version of ozone vertical profiles retrieved with the IMK/IAA (Institute for Meteorology and Climate Research/Instituto de Astrofísica de Andalucía) MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) research level 2 processor from version 5 spectral level 1 data. The time period covered corresponds to the reduced spectral resolution period of the MIPAS instrument, i.e., January 2005–April 2012. The comparison with satellite instruments includes all post-2005 satellite limb and occultation sensors that have measured the vertical profiles of tropospheric and stratospheric ozone: ACE-FTS, GOMOS, HALOE, HIRDLS, MLS, OSIRIS, POAM, SAGE II, SCIAMACHY, SMILES, and SMR. In addition, balloon-borne MkIV solar occultation measurements and ground-based Umkehr measurements have been included, as well as two nadir sensors: IASI and SBUV. For each reference data set, bias determination and precision assessment are performed. Better agreement with reference instruments than for the previous data version, V5R_O3_220 (Laeng et al., 2014), is found: the known high bias around the ozone vmr (volume mixing ratio) peak is significantly reduced and the vertical resolution at 35 km has been improved. The agreement with limb and solar occultation reference instruments that have a known small bias vs. ozonesondes is within 7% in the lower and middle stratosphere and 5% in the upper troposphere. Around the ozone vmr peak, the agreement with most of the satellite reference instruments is within 5%; this bias is as low as 3% for ACE-FTS, MLS, OSIRIS, POAM and SBUV.

Long-term changes in the upper stratospheric ozone at Syowa, Antarctica

Abstract. Analyses of stratospheric ozone data determined from Dobson–Umkehr measurements since 1977 at the Syowa (69.0° S, 39.6° E), Antarctica, station show a significant decrease in ozone at altitudes higher than that of the 4 hPa pressure level during the 1980s and 1990s. Ozone values over Syowa have remained low since 2001. The time series of upper stratospheric ozone from the homogenized NOAA SBUV (Solar Backscatter Ultraviolet Instrument)(/2) 8.6 overpass data (±4°, 24 h) are in qualitative agreement with those from the Syowa station data. Ozone recovery during the austral spring over the Syowa station appears to be slower than predicted by the equivalent effective stratospheric chlorine (EESC) curve. The long-term changes in the station's equivalent latitude (indicative of vortex size/position in winter and spring) are derived from MERRA (Modern Era Retrospective-analysis for Research and Applications) reanalyses at ~ 2 and ~ 50 hPa. These data are used to attribute some of the upper and middle stratospheric ozone changes to the changes in vortex position relative to the station's location. In addition, high correlation of the Southern Hemisphere annular mode (SAM) with polar upper stratospheric ozone during years of maximum solar activity points toward a strong relationship between the strength of the Brewer–Dobson circulation and the polar stratospheric ozone recovery. In the lower stratosphere, ozone recovery attributable to CFCs (chlorofluorocarbons) is still not definitive, whereas the recovery of the upper stratosphere is slower than predicted. Further research indicates that dynamical and other chemical changes in the atmosphere are delaying detection of recovery over this station.

Improvement of the Umkehr ozone profile by the neural network method: analysis of the Belsk (51.80°N, 20.80°E) Umkehr data

Vertical profiles of atmospheric ozone by the neural network (NN) method are compared with those obtained by the standard Umkehr inversion algorithm – UMK92. Both methods used the same input, the so-called N values, derived from Umkehr measurements at Belsk (51.80°N, 20.80°E), Poland, by the Dobson spectrophotometer No 84. The vertical profiles of ozone from satellite observations, Microwave Limb Sounder (MLS) overpasses for the period 2004–2009, and from ozonesoundings performed at the nearby aerological station, Legionowo (52.4° N, 21.0° E), for the period 2000–2009 provide a reference data set for the NN model building. The NN methodology appears to be a promising tool for extracting information about the vertical ozone profile from ground-based Umkehr measurements, despite some limitations of the NN method itself, such as the results being limited to the analysed station, sensitivity to errors in the reference data sets, and lack of possibility to determine the actual retrieval errors. Accuracy of the NN ozone profiles is better for all Umkehr layers than that by the standard Umkehr inversion algorithm when NN and UMK92 profiles are compared with the reference profiles. It is especially pronounced for comparisons with the ozonesonde profiles for layers 4 and 1, where the absolute error changes from 10.6 Dobson units (DU) (UMK92) to 4.4 DU (NN) and from 6.6 DU (UMK92) to 3.5 DU (NN), respectively (1 Dobson unit is equal to 2.69 × 1020 molecules/m2). The mean (over all Umkehr layers) correlation coefficient between NN-MLS, and NN-ozonesonde profiles is 0.75 and 0.85, respectively. The corresponding correlation coefficients for the comparison with UMK92 profiles are lower, i.e. 0.61 and 0.64, respectively.

Sensitivity of Dobson and Brewer Umkehr ozone profile retrievals to ozone cross-sections and stray light effects

Abstract. Remote sounding methods are used to derive ozone profile and column information from various ground-based and satellite measurements. Vertical ozone profiles measured in Dobson units (DU) are currently retrieved based on laboratory measurements of the ozone absorption cross-section spectrum between 270 and 400 nm published in 1985 by Bass and Paur (BP). Recently, the US National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) proposed using the set of ozone cross-section measurements made at the Daumont laboratory in 1992 (BDM) for revising the Aura Ozone Monitoring Instrument (OMI) and Global Ozone Monitoring Experiment (GOME) satellite ozone profiles and total ozone column retrievals. Dobson Umkehr zenith sky data have been collected by NOAA ground-based stations at Boulder, CO (BDR) and Mauna Loa Observatory, HI (MLO) since the 1980s. The UMK04 algorithm is based on the BP ozone cross-section data. It is currently used for all Dobson Umkehr data processing submitted to the World Ozone and Ultraviolet radiation Data Centre (WOUDC) under the Global Atmosphere Watch (GAW) program of the World Meteorological Organization (WMO). Ozone profiles are also retrieved from measurements by the Mark IV Brewers operated by the NOAA-EPA Brewer Spectrophotometer UV and Ozone Network (NEUBrew) using a modified UMK04 algorithm (O3BUmkehr v.2.6, Martin Stanek). This paper describes the sensitivity of the Umkehr retrievals with respect to the proposed ozone cross-section changes. It is found that the ozone cross-section choice only minimally (within the retrieval accuracy) affects the Dobson and the Brewer Umkehr retrievals. On the other hand, significantly larger errors were found in the MLO and Boulder Umkehr ozone data (−8 and +5% bias in stratosphere and troposphere respectively) when the out-of-band (OOB) stray light contribution to the Umkehr measurement is not taken into account (correction is currently not included in the UMK04). The vertical distribution of OOB effect in the retrieved profile can be related to the local ozone climatology, instrument degradation, and optical characteristics of the instrument. Nonetheless, recurring OOB errors do not contribute to the long-term ozone trends.

Coherence of long-term stratospheric ozone vertical distribution time series used for the study of ozone recovery at a northern mid-latitude station

Abstract. The coherence of stratospheric ozone time series retrieved from various observational records is investigated at Haute-Provence Observatory (OHP–43.93° N, 5.71° E). The analysis is accomplished through the intercomparison of collocated ozone measurements of Light Detection and Ranging (lidar) with Solar Backscatter UltraViolet(/2) (SBUV(/2)), Stratospheric Aerosol and Gas Experiment II (SAGE~II), Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS) on Upper Atmosphere Research Satellite (UARS) and Aura and Global Ozone Monitoring by Occultation of Stars (GOMOS) satellite observations as well as with in situ ozonesondes and ground-based Umkehr measurements performed at OHP. A detailed statistical study of the relative differences of ozone observations over the whole stratosphere is performed to detect any specific drift in the data. On average, all instruments show their best agreement with lidar at 20–40 km, where deviations are within ±5 %. Discrepancies are somewhat higher below 20 and above 40 km. The agreement with SAGE II data is remarkable since average differences are within ±1 % at 17–41 km. In contrast, Umkehr data underestimate systematically the lidar measurements in the whole stratosphere with a near zero bias at 16–8 hPa (~30 km). Drifts are estimated using simple linear regression for the data sets analysed in this study, from the monthly averaged difference time series. The derived values are less than ±0.5 % yr−1 in the 20–40 km altitude range and most drifts are not significant at the 2σ level. We also discuss the possibilities of extending the SAGE II and HALOE data with the GOMOS and Aura MLS data in consideration with relative offsets and drifts since the combination of such data sets are likely to be used for the study of stratospheric ozone recovery in the future.

Vertical ozone profile by Umkehr measurements at Syowa Station

Dobson Umkehr measurement for derivation of the vertical ozone profile has been conducted at Syowa station (69.0°S, 39.6°E) in Antarctica since 1977. Introduction of a highly automated measuring system in 1994 at Syowa has brought about many opportunities and high quality data acquisition for Umkehr measurements. Short Umkehr measurement (A, C and D pairs) has been routinely conducted at Syowa, where solar zenith angle is generally high, except for the polar summer when the solar zenith angle is too low. In this study, recently re-evaluated N-value records acquired at Syowa and the new algorithm UMK04 are used to deduce ozone profiles. The ozone hole in 2006 was developed to the largest size ever observed, and at Syowa the lowest total ozone of 114 DU since the beginning of observation was recorded. Umkehr measurements also show extremely low ozone amount in each layer above Syowa. This is the minimum record in Umkehr data at Syowa since the beginning of observation in 1977. The ozone profiles for recent years show decreasing tendency in spring in the upper (about 40 km) and lower stratosphere.

Comparison of ozone profiles by the Umkehr measurements taken at Belsk (52°N, 21°E) with the Aura Microwave Limb Sounder overpasses: 2004–2006

A comparison of ozone profile measurements by the Umkehr observations taken at Belsk (52°N, 21°E) by the Dobson spectrophotometer and collocated Earth Observing System (EOS) Microwave Limb Sounder (MLS) aboard the Aura platform during 2004–2006 site overpasses is presented. The MLS ozone vertical profiles from 1.5 and 2.2 retrieval algorithms and various Umkehr retrievals are considered. There is a good agreement between the ozone content in Umkehr layers. The mean difference ∼ ±5%, standard deviation of the relative differences < 10%, and the correlation coefficient > 0.5 are found in the midstratosphere (Umkehr layers 5–7) and in the upper stratosphere (combined layers 8, 9, and 10). In the lower stratosphere (combined layers 2 and 3 and layer 4) the mean difference and/or standard deviation are larger but the correlation coefficient is still high (∼0.8). Ozone content in Umkehr layers by integration of MLS version 1.5 and 2.2 ozone mixing ratio profiles behaves very similarly in the comparisons with the ground‐based data.

The 11‐year solar cycle in stratospheric ozone: Comparison between Umkehr and SBUVv8 and effects on surface erythemal irradiance

Ozone profiles derived from ground‐based Umkehr measurements at five stations and from the merged data set of Solar Backscattered Ultra Violet (SBUVv8) satellite observations are used to estimate the seasonal influence of the 11‐year solar signal in the vertical distribution of stratospheric ozone. Both data sets show a strong response (2–3% of the annual mean) in the upper stratosphere, a very small response in the middle tropical stratosphere and a secondary maximum (∼2%) in the tropical lower stratosphere, in accordance to earlier reports. Thus a sequence of high‐low‐high response is seen in the vertical pattern of the solar cycle effect on ozone in the tropics, with its position sensitive to season, as it appears to move across the equator in direction opposite to the location of the maximum solar insolation. Results from Umkehr and satellite observations are in good agreement at levels up to 35 km, while discrepancies (of up to 2%) found at higher levels (around 40 km) are largest in summer. Finally, the estimated erythemal irradiance response to the 11‐year solar cycle, calculated for the observed ozone change during a solar cycle (minimum to maximum), showed an overall decrease in the irradiance at the surface which is maximum (−2% of annual mean) over the tropics.

Preliminary comparison of the ozone vertical profiles from Umkehr and ozonesonde measurements over Poland with EOS‐MLS Aura spacecraft overpasses, 2004–2005

Ozone vertical profiles derived from Umkehr observations by the Dobson spectrophotometer at Belsk (52.50° N, 20.47° E) and from ozone soundings carried out at the nearest aerological station, Legionowo (52.24° N, 20.58° E), have been compared with those measured by the MLS instrument on board the Aura spacecraft during the sites' overpasses for the period 2004–2005. It is assumed that the satellite station distance should be less than 2° and less than 4° for the latitudinal and longitudinal difference, respectively. The bias, RMS error, and the correlation coefficients between the ozone content in the Umkehr layers have been calculated using Dobson/sonde/MLS data. The ozone mixing ratio at selected levels in the lower and mid‐stratosphere (from 215 hPa up to 6.8 hPa) have been compared using the sonde/MLS data. The number of analysed daily values was ∼40 (Dobson/MLS), 60 (sonde/MLS), and 60 (Dobson/sonde) since August 2004. The comparisons show a good correspondence (bias ∼±5%, RMS <10%, correlation coefficient >0.5) between the ozone content in Umkehr layers 4–8 and ozone mixing ratio at pressures <50 hPa. At lower stratosphere (Umkehr layer 3) and upper stratosphere (Umkehr layer 9), there is also statistically significant relationship between the data, but the biases and RMS are ∼2 times larger, while the correlation coefficients are still high (>0.7).

Estimating ozone variability and instrument uncertainties from SBUV(/2), ozonesonde, Umkehr, and SAGE II measurements: Short‐term variations

Coincident ozone measurements by the Solar Backscattered Ultra Violet (SBUV) and Stratospheric Aerosol and Gas Experiment (SAGE) II instruments and by ozonesondes and the Umkehr method are used to estimate stratospheric ozone variability and standard uncertainties of these different measurements. Below 20 km over northern midlatitudes, estimated measurement uncertainties for SBUV(/2), sondes, and Umkehr are similar (∼8% for 0 to 20 km integrated ozone), although only sondes have a high vertical resolution there. From 20 to 28 km., the estimated uncertainties (4–6%) for all four measurement sources are substantially smaller than the ozone variability in winter (10–15%), but they are comparable in summer (∼5%). Above 28 km, sonde uncertainties are larger than or comparable to the ozone variability, and much larger than uncertainties of SBUV(/2), Umkehr, or SAGE II data. Umkehr measurement uncertainties at 24–32 km are about 5% and are lower than sonde uncertainties (7–13%) at these levels. SBUV(/2) data are used to evaluate differences between different types of ozonesondes, and to show that correction by total ozone measurements noticeably reduces ozonesonde uncertainties. The latitudinal dependence of ozone variability and instrument uncertainties is studied using pairs of collocated SBUV(/2) and SAGE II measurements. There is good correlation between these measurements over middle and high latitudes. Over the tropical region, the correlation coefficients are modest (about 0.5) but significant in all layers except at 28–31 km. It is noted that where ozone variability is comparable to instrument uncertainties, comparison with a climatology based on a large number of observations may provide better insight into instrument performance than intercomparison of a small number of quasi‐coincident measurements.

Vertical ozone distribution characteristics deduced from ∼ 44,000 re-evaluated Umkehr profiles (1957-2000)

Umkehr observations taken during the 1957–2000 period at 15 stations located between 19 and 52° N have been reanalyzed using a significantly improved algorithm-99, developed by DeLuisi and Petropavlovskikh et al. (2000a,b). The alg-99 utilizes new latitudinal and seasonally dependent first guess ozone and temperature profiles, new vector radiative transfer code, complete aerosol corrections, gravimetric corrections, and others. Before reprocessing, all total ozone values as well as the N-values (radiance) readings were thoroughly re-evaluated. For the first time, shifts in the N-values were detected and provisionally corrected. The re-evaluated Umkehr data set was validated against satellite and ground based measurements. The retrievals with alg-99 show much closer agreement with the lidar and SAGE than with the alg-92. Although the latitudinal coverage is limited, this Umkehr data set contains ∼ 44,000 profiles and represent the longest (∼ 40 years) coherent information on the ozone behavior in the stratosphere of the Northern Hemisphere. The 14-months periods following the El-Chichon and the Mt. Pinatubo eruptions were excluded from the analysis. Then the basic climatological characteristics of the vertical ozone distribution in the 44–52° N and more southern locations are described. Some of these characteristics are not well known or impossible to be determined from satellites or single stations. The absolute and relative variability reach their maximum during winter–spring at altitudes below 24 km; the lower stratospheric layers in the middle latitudes contain ∼ 62% of the total ozone and contribute ∼ 57% to its total variability. The layer-5 (between ∼ 24 and 29 km) although containing 20% of the total ozone shows the least fluctuations, no trend and contributes only ∼ 11% to the total ozone variability. Meridional cross-sections from 19 to 52° N of the vertical ozone distribution and its variability illustrate the changes, and show poleward-decreasing altitude of the ozone maximum. The deduced trends above 33 km confirm a strong ozone decline since the mid-1970s of over 5% per decade without significant seasonal differences. In the mid-latitude stations, the decline in the 15–24 km layer is nearly twice as strong in the winter-spring season but much smaller in the summer and fall. The effect of including 1998 and 1999 years with relatively high total ozone data reduces the overall-declining trend. The trends estimated from alg-99 retrievals are statistically not significantly different from those in WMO 1998a; however, they are stronger by about 1% per decade in the lower stratosphere and thus closer to the estimates by sondes. Comparisons of the integrated ozone loss from the Umkehr measurements with the total ozone changes for the same periods at stations with good records show complete concurrence. The altitude and latitude appearances of the long-term geophysical signals like solar (1–2%) and QBO (2–7%) are investigated.

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.

A comparison of UV intensities calculated by spherical‐atmosphere radiation transfer codes: Application to the aerosol corrections

Various spherical radiative transfer (SRT) computer codes that model ultraviolet (UV) sky intensities incident at the Earth's surface are compared for clear‐sky (Rayleigh scattering and ozone absorption) and hazy‐sky (stratospheric volcanic aerosol, Rayleigh scattering, and ozone absorption) atmospheric conditions. Calculated sky intensities using Dave vector (pseudospherical), Dave scalar (pseudospherical), Herman's vector (full spherical), and Herman's scalar (full spherical) codes are compared for various parameters including solar zenith angle, direction of view, and wavelength. The differences in the calculated downward UV intensities are believed to arise from the differences in the code geometries and the neglect of polarization effects. The difference between downward UV intensities is within ±15% for clear‐sky conditions and between −30 and 18% for hazy‐sky conditions. The results of comparisons suggest that an experiment should be conducted to measure UV sky intensities for clear‐sky conditions, with minimal aerosol, to test the quality of the radiative transfer codes with actual observations. The Dave scalar radiative transfer code has been used in the past to calculate aerosol error corrections to Umkehr measurements. To evaluate the accuracy of these calculations, we performed a set of comparisons with results of various spherical radiative transfer codes. Ground level sky intensities were calculated for various solar zenith angle directions, for a vertically inhomogeneous Rayleigh atmosphere with ozone absorption, including and excluding stratospheric aerosols. For 0.11 stratospheric aerosol optical thickness, the method for calculating stratospheric aerosol errors to retrieved Umkehr ozone profile predicts either −22% or −32% error in layer 8 depending on whether vector or a scalar radiative transfer code had been used. The calculations were also used to study the effect of full spherical and pseudospherical forward model differences on Umkehr ozone profile retrievals. The difference in retrieved ozone profiles was found to be within ±4% for clear‐sky conditions and up to 13% in layer 8 for hazy‐sky conditions. The results of these comparisons suggest that further improvements to the profile retrieval and stratospheric aerosol error calculations could be made using a fully spherical RT code that accounts for polarization.

ミリ波地上分光観測による成層圏・中間圏オゾンの変動

Comparison of strato-mesospheric O 3 derived from ground-based microwave radiometry at Nagoya University with Umkehr measurements at Tsukuba by JMA (Japan Meteorological Agency) has been carried out for evaluation of microwave measurements. Good agreements between radio and Umkehr measurements have been found from Umkehr layer 6-9, which correspond to the pressure of 15.8-0.99 hPa. Layer ozone amounts in layer 10 from microwave measurements show short term enrichment in winter with time scale of about a week, which are not observed by Umkehr measurements. The difference is due to the saturation effect inherent in Umkehr measurements. Fourier coefficients, up to the 2nd harmonic of the seasonal variations of nighttime and daytime mixing ratios, are given in tables for the pressure P = 0.013,... 10 hPa (log P = -1.875,., 1.000). QBO type variations of O 3 in 1-0.1 hPa range described in our earlier paper are due to the superposition of the short term enrichment. The short term enrichment was especially remarkable in 1992-1993 and 1994-1995. The short term enrichment does not correlate with temperature. A plausible cause of the enrichment will be vertical circulation anomalies as is they case of QBO variations in O 3 at the lower-stratosphere, and in NO 2 at the middle-stratosphere proposed by Randel and Wu (1996).

Results from the 1995 Stratospheric Ozone Profile Intercomparison at Mauna Loa

In August 1995, multiple instruments that measure the stratospheric ozone vertical distribution were intercompared at the Mauna Loa Observatory, Hawaii, under the auspices of the Network for the Detection of Stratospheric Change. The instruments included two UV lidar systems, one from the Jet Propulsion Laboratory and the other from Goddard Space Flight Center, electrochemical concentration cell balloon sondes, a ground‐based microwave instrument, Dobson‐based Umkehr measurements, and a new ground‐based Fourier transform infrared instrument. The Microwave Limb Sounder instrument on the Upper Atmosphere Research Satellite provided correlative profiles of ozone, and there was one close overpass of the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument. The results show that much better consistency among instruments is being achieved than even a few years ago, usually to within the instrument uncertainties. The different measurement techniques in this comparison agree to within ±10% at almost all altitudes, and in the 20–45 km region most agreed within ±5%. The results show that the current generation of lidars is capable of accurate measurement of the ozone profile to a maximum altitude of 50 km. SAGE II agreed well with both lidar and balloon sonde down to at least 17 km. The ground‐based microwave measurement agreed with other measurements from 22 km to above 50 km. One minor source of disagreement continues to be the pressure‐altitude conversion needed to compare a measurement of ozone density versus altitude with a measurement of ozone mixing ratio versus pressure.

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.

Rocket soundings of ozone profiles in the stratosphere over the Korean Peninsula

Two stratospheric ozone profiles have been obtained using rocket‐based solar absorption UV radiometry over Anheung, Korea on June 4 and September 1, 1993. The ozone sensor consists of four radiometers, measuring the attenuation of solar ultraviolet radiation as a function of altitude during ascent. The retrieved ozone density profiles cover altitudes of 15 to 35 km from the first sounding Korean Sounding Rocket‐1 (KSR‐1 ) and 15 to 45 km from the second sounding (KSR‐2). Retrieved profiles have random errors (1σ) of approximately 7% for altitudes between 20 and 30 km for KSR‐1 and between 20 and 40 km for KSR‐2 and ∼15–20% for other regions. Both profiles compare reasonably well with near‐coincident ground‐based lidar and Umkehr measurements as well as with satellite measurements of the Halogen Occultation Experiment on board UARS. The KSR‐1 and KSR‐2 soundings provided the first near in situ measurements of ozone concentrations over the Korean Peninsula. The significance of these measurements at this geographical location will be discussed.