1Department of Earth and Space Sciences, Chalmers University of Technology, Gothenburg, Sweden
2National Institute of Information and Communications Technology, Tokyo, Japan
3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
4Department of Physics, University of Toronto, Toronto, Ontario, Canada
5Tokyo Institute of Technology, Yokohama, Kanagawa, Japan
6Fujitsu FIP Corporation, Tokyo, Japan
7Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto, Japan
8Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, Japan
9Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Karlsruhe, Germany
Received: 10 May 2012 – Discussion started: 20 Aug 2012
Abstract. 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 photochemical 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 Station, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT, and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on board SCISAT. Inter-comparison of the measurements from instruments on sun-synchronous satellites (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 measured at all local times over a period of several months provides the possibility to verify the model and to indirectly compare the diurnally variable species. The satellite data were averaged for latitudes of 20° S to 20° N for the SMILES observation period from November 2009 to April 2010 and were compared at three altitudes: 35, 45 and 55 km. Besides presenting the SMILES data, the study also shows a first comparison of the latest MLS data (version 3.3) of HOCl, ClO, and HO2 with other satellite observations, as well as a first evaluation of HO2 observations made by Odin/SMR. The MISU-1D model has been carefully initialised and run for conditions and locations of the observations. The diurnal cycle features for the species investigated here are generally well reproduced by the model. The satellite observations and the model agree well in terms of absolute mixing ratios. The differences between the day and night values of the model are in good agreement with the observations although the amplitude of the HO2 diurnal variation is 10–20% lower in the model than in the observations. In particular, the data offered the opportunity to study the reaction ClO+HO2 → HOCl+O2 in the lower mesosphere at 55 km. At this altitude the HOCl night-time variation depends only on this reaction. The result of this analysis points towards a value of the rate constant within the range of the JPL 2006 recommendation and the upper uncertainty limit of the JPL 2011 recommendation at 55 km.
Revised: 29 May 2013 – Accepted: 18 Jun 2013 – Published: 06 Aug 2013
Khosravi, M., Baron, P., Urban, J., Froidevaux, L., Jonsson, A. I., Kasai, Y., Kuribayashi, K., Mitsuda, C., Murtagh, D. P., Sagawa, H., Santee, M. L., Sato, T. O., Shiotani, M., Suzuki, M., von Clarmann, T., Walker, K. A., and Wang, S.: Diurnal variation of stratospheric and lower mesospheric HOCl, ClO and HO2 at the equator: comparison of 1-D model calculations with measurements by satellite instruments, Atmos. Chem. Phys., 13, 7587-7606, doi:10.5194/acp-13-7587-2013, 2013.