MIPAS IMK/IAA Carbon Tetrachloride (CCl4) Retrieval

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Eckert, Ellen ; Clarmann, Thomas ; Laeng, Alexandra ; Stiller, Gabriele P. ; Funke, Bernd ; Glatthor, Norbert ; Grabowski, Udo ; Kellmann, Sylvia ; Kiefer, Michael ; Linden, Andrea ; Wetzel, Gerald ; Boone, Christopher ; Engel, Andreas ; Harrison, Jeremy J. ; Sheese, Patrick E. ; Walker, Kaley A. ; Bernath, Peter F. (2017)

MIPAS thermal limb emission measurements were used to derive vertically resolved profiles of carbon tetrachloride (CCl<sub>4</sub>). Level-1b data versions MIPAS/5.02 to MIPAS/5.06 were converted into profiles using the level-2 processor developed at Karlsruhe Institute of Technology (KIT) Institute of Meteorology and Climate Research (IMK) and Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Astrofísica de Andalucía (IAA). Consideration of peroxyacetyl nitrate (PAN) as interfering species, which is jointly retrieved and CO<sub>2</sub> line mixing, was found to be crucial for reliable retrievals. Parts of the CO<sub>2</sub> Q-branch region that overlap with the CCl<sub>4</sub> signature were omitted, since large residuals were still found even though line mixing was considered in the forward model. However, the omitted spectral region could be narrowed considerably when line mixing was a<sub>4</sub>4 volume mixing ratios. In general, latitude-altitude cross-section show the expected CCl<sub>4</sub> features with highest values of around 90&thinsp;pptv at altitudes at and below the tropical tropopause and values decreasing with altitude and latitude due to stratospheric decomposition. Other patterns, such as subsidence in the polar vortex during winter and early spring, are also visible in the distributions. The decline in CCl<sub>4</sub> abundance during the MIPAS Envisat measurement period (July 2002 to April 2012) is clearly reflected in the retrieved distributions.
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