Diurnal variation of stratospheric and lower mesospheric HOCl, ClO and HO 2 at the equator: comparison of 1-D model calculations with measurements by satellite instruments

The diurnal variation of HOCl and the related species ClO, HO2 and HCl measured by satellites has been compared with the results of a one-dimensional photochem- ical model. The study compares the data from various limb- viewing instruments with model simulations from the middle stratosphere to the lower mesosphere. Data from three sub- millimetre instruments and two infrared spectrometers are used, namely from the Sub-Millimetre Radiometer (SMR) on board Odin, the Microwave Limb Sounder (MLS) on board Aura, the Superconducting Submillimeter-wave Limb- Emission Sounder (SMILES) on the International Space Sta- tion, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT, and the Atmo- spheric Chemistry Experiment Fourier Transform Spectrom- eter (ACE-FTS) on board SCISAT. Inter-comparison of the measurements from instruments on sun-synchronous satel- lites (SMR, MLS, MIPAS) and measurements from solar occultation instruments (ACE-FTS) is challenging since the measurements correspond to different solar zenith angles (or local times). However, using a model which covers all solar zenith angles and data from the SMILES instrument which