Investigating the long-term evolution of subtropical ozone profiles applying ground-based FTIR spectrometry

[摘要] This study investigates the long-term evolution of subtropical ozone profiletime series (1999–2010) obtained from ground-based FTIR (Fourier TransformInfraRed) spectrometry at the Izaña Observatory ozone super-site.Different ozone retrieval strategies are examined, analysing the influence ofan additional temperature retrieval and different constraints. Thetheoretical assessment reveals that the FTIR system is able to resolve fourindependent ozone layers with a precision of better than 6% in thetroposphere and of better than 3% in the lower, middle and upperstratosphere. This total error includes the smoothing error, which dominatesthe random error budget. Furthermore, we estimate that the measurement noiseas well as uncertainties in the applied atmospheric temperature profiles andinstrumental line shape are leading error sources. We show that asimultaneous temperature retrieval can significantly reduce the total randomerrors and that a regular determination of the instrumental line shape isimportant for producing a consistent long-term dataset. These theoreticalprecision estimates are empirically confirmed by daily intercomparisons withElectro Chemical Cell (ECC) sonde profiles. In order to empirically documentthe long-term stability of the FTIR ozone profile data we compare the lineartrends and seasonal cycles as obtained from the FTIR and ECC time series.Concerning seasonality, in winter both techniques observe stratospheric ozoneprofiles that are typical middle latitude profiles (low tropopause, low ozonemaximum concentrations) and in summer/autumn profiles that are typicaltropical profiles (high tropopause, high maximum concentrations). The lineartrends estimated from the FTIR and the ECC datasets agree within their errorbars. For the FTIR time series, we observe a significantnegativetrend in the upper troposphere/lower stratosphere of about−0.2% yr⁻¹ and a significant positive trend in the middle andupper stratosphere of about +0.3% yr⁻¹ and +0.4% yr⁻¹,respectively. Identifying such small trends is a difficult task for anymeasurement technique. In this context, super-sites applying differenttechniques are very important for the detection of reliable ozone trends.

[学科分类] 几何与拓扑