Comparison of SMILES ClO profiles with other satellite and balloon-based measurements

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 error analysis simulations 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 JAXA within of the bias uncertainties, except for the nighttime measurements in the low and middle latitude region 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, which makes it difficult to distinguish between the 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 datasets from other instruments such as the Aura Microwave Limb Sounder (MLS), the Odin Sub-Millimetre Radiometer (SMR), and the Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), 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 0.3 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 (MIPAS-B).