Comparison of SMILES ClO profiles with satellite, balloon-borne and ground-based measurements

We evaluate the quality of ClO profiles de- rived from the Superconducting Submillimeter-Wave Limb- Emission Sounder (SMILES) on the International Space Sta- tion (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 measure- ments, a systematic error of 8 pptv was estimated for the ClO peak altitude ( 2 hPa). The SMILES NICT v2.1.5 ClO pro- files agree with those derived from another level-2 proces- sor developed by the Japan Aerospace Exploration Agency (JAXA) within the bias uncertainties, except for the night- time 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 re- trieval process of SMILES NICT v2.1.5, which makes it dif- ficult 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 instru- ments 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 pro- files show larger volume mixing ratios by 0.4 ppbv (30 %) at 50 hPa compared to those of the JAXA processed pro- files. 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 analy- sis.