Heidelberg 2015 – wissenschaftliches Programm
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UP: Fachverband Umweltphysik
UP 2: Atmosphäre
UP 2.12: Vortrag
Mittwoch, 25. März 2015, 12:30–12:45, G/gHS
Retrieval of atmospheric methane from mid-infrared FTIR spectrometry optimized for profile information content and minimal cross-sensitivity to water vapor — •Petra Hausmann and Ralf Sussmann — Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany
Mid-infrared ground-based solar FTIR measurements performed within the Network for the Detection of Atmospheric Composition Change (NDACC) contain information on total columns which can be used for source-sink inversions or satellite validation. Additionally, mid-infrared FTIR is one of the few ground-based techniques containing information on the CH4 vertical profile. Previous retrievals were optimized for high-accuracy columns and eliminating water vapor interference (Sussmann et al., 2011), or for separating the tropospheric partial column (Sepulveda et al., 2014). The goal of our present study is to combine the benefits of these approaches in order to attain maximum profile information and simultaneously minimize cross-sensitivity to water vapor. We apply a 3-block first-order Tikhonov regularization to make best possible use of the profile information contained in the spectra and separate a tropospheric and stratospheric column. We analyze almost 20 years of FTIR measurements at Zugspitze (47∘ N, 2964 m a.s.l.) with our new retrieval and provide time series of CH4 partial columns, profiles, and multi-annual seasonal cycles. Our results may be used to quantify trends of stratospheric methane oxidation and corresponding production of water vapor in the highly climate-sensitive region of the lower stratosphere.