Technical Note: Intercomparison of ILAS-II version 2 and 1.4 trace species with MIPAS-B measurements

Abstract

(Sweden, 68 • N) at virtually the same location that has been sounded by ILAS-II about 5.5 h prior to the sampling of MIPAS-B. The intercomparison of the new ILAS-II version 2 (Northern Hemispheric sunrise) data to MIPAS-B vertical trace gas profiles shows a good to excellent agreement within the combined error limits for the species O 3 , N 2 O, CH 4 , H 2 O (above 21 km), HNO 3 , ClONO 2 , and CFC-11 (CCl 3 F) in the compared altitude range between 16 and 31 km such that these data appear to be very useful for scientific analysis. With regard to the previous version 1.4 ILAS-II data, significant improvements in the consistency with MIPAS-B are obvious especially for the species CH 4 and H 2 O, but also for O 3 , HNO 3 , ClONO 2 , NO 2 , and N 2 O 5 . However, comparing gases like NO 2 , N 2 O 5 , and CFC-12 (CCl 2 F 2 ) exhibits only poor agreement with MIPAS-B such that these species cannot be assumed to be validated at the present time.

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

“…This is the first comparison with the newest version of the ILAS-II CFC-11 and CFC-12 data (version 3). However, a similar feature has already been seen in comparisons of ILAS-II CFC-11 version 1.4 and version 2 measurements with MIPAS-B (Wetzel et al, 2008). The differences of MIPAS and ILAS-II exceed those of other comparisons by far.…”

“…15 demonstrates that the combined error of the two instruments (purple line) is far larger than the standard deviation of the differences (brown line), we suspect that the ILAS-II errors are largely overestimated. Above 20 km, Wetzel et al (2008) also found higher mixing ratios. All in all, the agreement of MI-PAS CFC-11 measurements taken during the FR period with those of ILAS-II is not good as it shows far larger differences at the bottom end of the profile than comparisons with, e.g., ACE-FTS or HATS, that are as big as 50 % and also large deviations at the upper end of the profiles that exceed 100 % above 25 km.…”

“…These differences stay mainly within 50 pptv, corresponding to 25 % at the largest. Larger differences appear in the comparison with ILAS-II, but we suggest treating these results with care since Wetzel et al (2008) found similarly large differences when comparing MIPAS-B results to a former version of ILAS-II measurements. Differences in CFC-11 tend to be smaller than 30 pptv above 15 km in most cases for the RR period, which corresponds to approximately 20 % at the largest.…”

“…Another conspicuous feature of this comparison is the very large error bars estimated from the ILAS-II retrieval (left panel: horizontal black and blue lines). However, Wetzel et al (2008) show similarly large error bars in their comparison of the former version of ILAS-II with MIPAS-B data. Since the right panel of Fig.…”

“…From 17 km upwards however, deviations can be as large as close to 150 pptv around 25 km, resulting in relative differences of over 100 %. Wetzel et al (2008) While MIPAS oscillates around a constant mixing ratio of approximately 550 pptv at 3 km below the tropopause, the HATS ground-based measurements show mixing ratios well within the range of 540 to 545 pptv. Thus, the difference between MIPAS and HATS is very small, of an order of ∼ 10 pptv at the largest, which corresponds to relative differences of less than 2 %.…”