Deliverables Total ozone and raw Umkehr re-evaluation. Ozone data processing In order to achieve a coherent and homogeneous Umkehr data set, several controls were performed on the data deposited at the WOUDC (World Ozone and UV Data Centre) archive in Toronto: In the Umkehr method, the measurement correspond to the variation of the ratio of two zenith-sky UV intensities at selected wavelengths with solar zenith angle (SZA) changing from 60 degrees to 90 degrees. A thorough review of the individual readings from the Dobson instruments for all the SZA was performed, with in parallel, the re- examination of the calibration records of all Dobson stations made during past inter-comparisons and total ozone re-evaluations. A number of "shifts" in the individual SZA data were identified and suggestions for homogenisation of the original raw data accounting for the various "shifts" were made. In addition, the total ozone records were re-evaluated and a rigid quality control of the Umkehr ozone profiles was applied: from over 60,000 Umkehr profiles deposited initially in the WOUDC archive, 40,000 were finally selected for the REVUE statistical and long-term analysis. Validation of the Umkehr data against ancillary measurements The new Umkehr data set was validated against long-term measurements such as the SAGE II satellite measurements taken at the vicinity of each station and in the case of the Haute-Provence Observatory, the ozone sondes and stratospheric ozone lidar measurements. In most stations, the new algorithm shows a better agreement with SAGE in layer 3. In layer 4, the new Umkehr retrieval provide lower ozone amounts which result in a small negative bias of the Umkehr data with respect to SAGE II. The best agreement is found in layer 5 to 7, the optimal range of the Umkehr algorithm in terms of information content. In stations with less reliable Umkehr records, the new algorithm improves the agreement with the SAGE II data. In Tenerife, the local Brewer Umkehr measurements were compared to ozone sondes measurements. Several version of the Brewer Umkehr were analysed. The comparisons showed that the early Wave5 version (1991) provides the best results. Wave5 (1994) and Wave6 do not improve Umkehr profiles and introduce some uncertainties. A new ozone first-guess obtained from the ECC climatology was incorporated to the Wave5 (1991) code, improving significantly the results. An analysis of possible Umkehr quality control indexes including cloud monitoring was also performed. Improved Dobson Umkher retrieval algorithm The Umkehr ozone profile retrieval algorithm uses a first-guess ozone profile and radiation measurements. The retrieval then seeks to effect a change to the first-guess profile from the information contained in the radiation measurement, with the covariance information telling the algorithm the most probable changes to the ozone profile. In the course of the REVUE project, a new first-guess data set based on updated ozone sondes and SAGE II climatology was produced. A study of the importance of a priori information on the Umkehr retrieval algorithm was also performed. Latitudinal dependant temperature climatology is now used in the Umkehr algorithm instead of one global temperature profile. The effect of this improvement on the retrieved ozone profiles was evaluated. In the new algorithm, the procedure has been changed to adopt the more accurate radiation transfer vector code of Dave, instead of the scalar code from the same author, for the theoretical calculations of Umkehr raw data (N-values). The Dave's scalar RT code used in the past lacked the necessary accuracy that enables the algorithm to calculate accurate multiple-scattering corrections for retrieved ozone profile. Statistical analysis of the ozone Umkher time series and ozone trend re-evaluation The statistical calculations and trends that have been produced from the revised Umkehr data set cover two periods: 1978-97 and 1964-99. The statistical analysis of the ozone variability shows that the absolute and relative variability reach their maximum during winter-spring in the altitudes below 24 km. Two-thirds of the total ozone variability is contributed by these layers. Layer 5 (24-29 km) although containing about 20% of the total ozone shows the least fluctuations, no trend and contributes only approximately 7% to the total ozone variability. The deduced trends above 30 km confirm strong ozone decline since mid-1970s of over 6% per decade without significant seasonal differences. In the northern mid-latitude stations in the 15-24 km layer, the decline is nearly twice as strong in the winter-spring season but much smaller in the summer and fall. Adding two more years of data in 1998 and 1999, characterised by a relatively high total ozone reduced by nearly one half the negative trend rates in the lower stratosphere but did not change significantly the rates in the upper stratosphere. Stratospheric aerosol climatology The aerosol correction is of prime importance in the Umkehr retrieval, since the long-term records are perturbed in the lowermost and uppermost layers, by the volcanic aerosols originated in the stratosphere from the eruptions of several volcanoes such as El Chichon in 1982 and Mount Pinatubo in 1991. These eruptions injected high amounts of sulphur that ended up in the formation of intense volcanic clouds lasting about 3 years in the lower stratosphere. A large set of aerosol profiles from the SAGE satellite climatology, backscatter lidar and sun-photometry measurements .was put together in order to calculate aerosol error corrections as a function of stratospheric aerosol optical depth. A significant part of this study involved examination of the relationships between aerosol size distribution and extinction as well as other optical properties as a function of wavelength, in order to estimate the aerosol extinction at the UV wavelengths used in the Umkehr measurements. Searching for OpenAIRE data... There was an error trying to search data from OpenAIRE No results available
