MIPAS IMK/IAA CFC-11 (CCl₃F) and CFC-12 (CCl₂F₂) measurements: accuracy, precision and long-term stability

Abstract

) and were used to validate MIPAS CFC-11 and CFC-12 products during that time, as well as profiles from the Improved Limb Atmospheric Spectrometer, ILAS-II. In general, we find that MIPAS shows slightly higher values for CFC-11 at the lower end of the profiles (below ∼ 15 km) and in a comparison of HATS ground-based data and MIPAS measurements at 3 km below the tropopause. Differences range from approximately 10 to 50 pptv (∼ 5-20 %) during the RR period. In general, differences are slightly smaller for the FR period. An indication of a slight high bias at the lower end of the profile exists for CFC-12 as well, but this bias is far less pronounced than for CFC-11 and is not as obvious in the relative differences between MIPAS and any of the comparison instruments. Differences at the lower end of the profile (below ∼ 15 km) and in the comparison of HATS and MIPAS measurements taken at 3 km below the tropopause mainly stay within 10-50 pptv (corresponding to ∼ 2-10 % for CFCPublished by Copernicus Publications on behalf of the European Geosciences Union. 3356 E. Eckert et al.: MIPAS IMK/IAA CFC-11 and CFC-12: accuracy, precision and long-term stability 12) for the RR and the FR period. Between ∼ 15 and 30 km, most comparisons agree within 10-20 pptv (10-20 %), apart from ILAS-II, which shows large differences above ∼ 17 km. Overall, relative differences are usually smaller for CFC-12 than for CFC-11. For both species -CFC-11 and CFC-12 -we find that differences at the lower end of the profile tend to be larger at higher latitudes than in tropical and subtropical regions. In addition, MIPAS profiles have a maximum in their mixing ratio around the tropopause, which is most obvious in tropical mean profiles. Comparisons of the standard deviation in a quiescent atmosphere (polar summer) show that only the CFC-12 FR error budget can fully explain the observed variability, while for the other products (CFC-11 FR and RR and CFC-12 RR) only two-thirds to three-quarters can be explained. Investigations regarding the temporal stability show very small negative drifts in MIPAS CFC-11 measurements. These instrument drifts vary between ∼ 1 and 3 % decade −1 . For CFC-12, the drifts are also negative and close to zero up to ∼ 30 km. Above that altitude, larger drifts of up to ∼ 50 % decade −1 appear which are negative up to ∼ 35 km and positive, but of a similar magnitude, above.

MIPAS IMK/IAA Carbon Tetrachloride (CCl4) Retrieval

“…It is clearly visible that 310 the closest MIPAS profile produced with the new spectroscopic data comes closer to the Cryosampler measurements, even though these still show slightly lower volume mixing ratios of CCl 4 . A similar pattern of two outliers (second and forth lowest Cryosampler measurements) were also seen in a comparison of Cryosampler and MIPAS measurements of CFC-11 and CFC-12 (Eckert et al, 2016), even though the second lowest outlier is not as obvious for the CFCs. However, this might 315 be an indication that Cryosampler captured fine structures (like laminae) produced by the unique 15 Atmos.…”

CCl<sub>4</sub> distribution derived from MIPAS ESA v7 data: intercomparisons, trend, and lifetime estimation

“…MIPAS Level 1b radiances version 5 were used in the past to extract information on trends of different gases, either ignoring this effect (see, e.g., CFC-11/CFC-12 in Kellmann et al, 2012, or HCFC-22 in Chirkov et al, 2016 or correcting the drift via intercomparison with other instruments assumed to be drift-free (Eckert et al, 2014). Recently it has been shown (Eckert et al, 2016) that ignoring this effect introduces a significant error on the trend estimation. The MIPAS Level 1b calibrated radiances version 7 employed here are considered to be a significant improvement from the point of view of the correction of this drift.…”

MIPAS IMK/IAA carbon tetrachloride (CCl4) retrieval and first comparison with other instruments

“…It is clearly visible that the closest MIPAS profile produced with the new spectroscopic data comes closer to the cryosampler measurements, even though these still show slightly lower volume mixing ratios of CCl 4 . A similar pattern of two outliers (second and forth lowest cryosampler measurements) was also seen in a comparison of cryosampler and MIPAS measurements of CFC-11 and CFC-12 (Eckert et al, 2016), even though the second lowest outlier is not as obvious for the CFCs. However, this might be an indication that cryosampler captured fine structures (like laminae) produced by the unique atmospheric situation in spring 2011 (Manney et al, 2011;Sinnhuber et al, 2011), which MIPAS Envisat cannot resolve due to its coarser vertical resolution.…”