Abstract
Abstract. Within the European project UFTIR (Time series of Upper Free Troposphere observations from an European ground-based FTIR network), six ground-based stations in Western Europe, from 79° N to 28° N, all equipped with Fourier Transform infrared (FTIR) instruments and part of the Network for the Detection of Atmospheric Composition Change (NDACC), have joined their efforts to evaluate the trends of several direct and indirect greenhouse gases over the period 1995–2004. The retrievals of CO, CH4, C2H6, N2O, CHClF2, and O3 have been optimized. Using the optimal estimation method, some vertical information can be obtained in addition to total column amounts. A bootstrap resampling method has been implemented to determine annual partial and total column trends for the target gases. The present work focuses on the ozone results. The retrieved time series of partial and total ozone columns are validated with ground-based correlative data (Brewer, Dobson, UV-Vis, ozonesondes, and Lidar). The observed total column ozone trends are in agreement with previous studies: 1) no total column ozone trend is seen at the lowest latitude station Izaña (28° N); 2) slightly positive total column trends are seen at the two mid-latitude stations Zugspitze and Jungfraujoch (47° N), only one of them being significant; 3) the highest latitude stations Harestua (60° N), Kiruna (68° N) and Ny-Ålesund (79° N) show significant positive total column trends. Following the vertical information contained in the ozone FTIR retrievals, we provide partial columns trends for the layers: ground-10 km, 10–18 km, 18–27 km, and 27–42 km, which helps to distinguish the contributions from dynamical and chemical changes on the total column ozone trends. We obtain no statistically significant trends in the ground-10 km layer for five out of the six ground-based stations. We find significant positive trends for the lowermost stratosphere at the two mid-latitude stations, and at Ny-Ålesund. We find smaller, but significant trends for the 18–27 km layer at Kiruna, Harestua, Jungfraujoch, and Izaña. The results for the upper layer are quite contrasted: we find significant positive trends at Kiruna, Harestua, and Jungfraujoch, and significant negative trends at Zugspitze and Izaña. These ozone partial columns trends are discussed and compared with previous studies.
Highlights
The increase of radiatively active gases in the atmosphere and their impact on climate changes are among the most important environmental problems of today
Within the framework of the European project UFTIR2 (Time series of Upper Free Troposphere observations from a European ground-based FTIR network), presented in De Maziere et al (2005), six g-b FTIR stations have joined their efforts to evaluate the trends over the period 1995–2004 of several direct and indirect greenhouse gases
We demonstrate that time series of g-b FTIR measurements are very suitable for studying the vertical distribution of stratospheric ozone trends since they can provide independent ozone partial columns amounts in three different altitude layers in the stratosphere
Summary
The increase of radiatively active gases in the atmosphere and their impact on climate changes are among the most important environmental problems of today. A bootstrap resampling method has been applied to the time series of these abundances in order to obtain tropospheric, stratospheric and total column trends. This method is described in Gardiner et al (2008). We demonstrate that time series of g-b FTIR measurements are very suitable for studying the vertical distribution of stratospheric ozone trends since they can provide independent ozone partial columns amounts in three different altitude layers in the stratosphere. Since the observed trends seem to vary depending on the studies, even in close locations at NH mid-latitudes, our UFTIR data set from six FTIR stations in Europe provides an important contribution to the study of ozone trends in the troposphere.
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