Abstract
Abstract. We evaluate the quality of ClO profiles derived from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station (ISS). Version 2.1.5 of the level-2 product generated by the National Institute of Information and Communications Technology (NICT) is the subject of this study. Based on sensitivity studies, the systematic error was estimated as 5–10 pptv at the pressure range of 80–20 hPa, 35 pptv at the ClO peak altitude (~ 4 hPa), and 5–10 pptv at pressures ≤ 0.5 hPa for daytime mid-latitude conditions. For nighttime measurements, a systematic error of 8 pptv was estimated for the ClO peak altitude (~ 2 hPa). The SMILES NICT v2.1.5 ClO profiles agree with those derived from another level-2 processor developed by the Japan Aerospace Exploration Agency (JAXA) within the bias uncertainties, except for the nighttime measurements in the low and middle latitude regions where the SMILES NICT v2.1.5 profiles have a negative bias of ~ 30 pptv in the lower stratosphere. This bias is considered to be due to the use of a limited spectral bandwidth in the retrieval process of SMILES NICT v2.1.5, which makes it difficult to distinguish between the weak ClO signal and wing contributions of spectral features outside the bandwidth. In the middle and upper stratosphere outside the polar regions, no significant systematic bias was found for the SMILES NICT ClO profile with respect to data sets from other instruments such as the Aura Microwave Limb Sounder (MLS), the Odin Sub-Millimetre Radiometer (SMR), the Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), and the ground-based radiometer at Mauna Kea, which demonstrates the scientific usability of the SMILES ClO data including the diurnal variations. Inside the chlorine-activated polar vortex, the SMILES NICT v2.1.5 ClO profiles show larger volume mixing ratios by 0.4 ppbv (30%) at 50 hPa compared to those of the JAXA processed profiles. This discrepancy is also considered to be an effect of the limited spectral bandwidth in the retrieval processing. We also compared the SMILES NICT ClO profiles of chlorine-activated polar vortex conditions with those measured by the balloon-borne instruments: Terahertz and submillimeter Limb Sounder (TELIS) and the MIPAS-balloon instrument (MIPAS-B). In conclusion, the SMILES NICT v2.1.5 ClO data can be used at pressures ≤ ~30 hPa for scientific analysis.
Highlights
Chlorine monoxide (ClO) is one of the key species for the ozone depletion mechanism in the stratosphere, participating in the reaction cycle as the primary element of the reactive chlorine family (e.g., Molina and Rowland, 1974)
We evaluate the quality of ClO profiles derived from the Superconducting Submillimeter-Wave LimbEmission Sounder (SMILES) on the International Space Station (ISS)
The SMILES National Institute of Information and Communications Technology (NICT) v2.1.5 ClO profiles agree with those derived from another level-2 processor developed by the Japan Aerospace Exploration Agency (JAXA) within the bias uncertainties, except for the nighttime measurements in the low and middle latitude regions where the SMILES NICT v2.1.5 profiles have a negative bias of ∼ 30 pptv in the lower stratosphere
Summary
Chlorine monoxide (ClO) is one of the key species for the ozone depletion mechanism in the stratosphere, participating in the reaction cycle as the primary element of the reactive chlorine family (e.g., Molina and Rowland, 1974). Its scientific findings are outside the scope of this paper, the SMILES ClO measurements provided several interesting insights into the stratospheric and mesospheric researches such as the global distribution of ClO in the middle atmosphere and its diurnal variations. In association with the error analysis by Sato et al (2012), we intend in this paper to evaluate the quality of the SMILES ClO data generated by the NICT level-2 processing by comparing it with those obtained by the following instruments: Aura MLS, Odin SMR, Envisat MIPAS, TELIS, the balloonborne MIPAS (MIPAS-B) and the ground-based radiometer at the Mauna Kea observatory.
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