Brice Barret

Retrieval and characterization of ozone vertical profiles from a thermal infrared nadir sounder

Received 27 February 2005; revised 15 September 2005; accepted 13 October 2005; published 17 December 2005. [1] This paper presents the first retrievals and validations of ozone vertical distributions from a set of high-resolution nadir thermal infrared measurements. These were obtained by the Interferometric Monitor for Greenhouse gases (IMG) instrument, which has operated on board the Japanese ADEOS platform between 1996 and 1997. The Optimal Estimation Method is used for the retrievals, along with a priori profile and covariance matrix built from model climatologies. We compare the retrieved IMG profiles with high-vertical-resolution ozone sonde measurements. Therefore we selected a set of IMG spectra collocated to within 3� of longitude and latitude with a representative distribution of ground-based stations. We demonstrate that thanks to the two to four independent pieces of vertical information contained in the spectroscopic measurements with a maximum sensitivity in the upper troposphere–middle stratosphere, the thermal infrared nadir sounders are able to capture most of the ozone spatial and temporal variations. In particular, the latitudinal variations of the stratospheric ozone maximum are well represented in the retrievals, as are the high ozone concentrations observed in the upper troposphere–lower stratosphere at northern midlatitudes during springtime. Ozone depletion events in the Arctic vortex are also well reproduced. The measurements provide an accurate view of the tropospheric ozone content, except when the latter is very low. A detailed error budget reveals that the major part of the error in the IMG retrieved ozone profile is due to the smoothing of the true profile by the averaging kernel matrix, with additional contributions associated with the measurement noise and the inaccurate knowledge of the temperature profile and of the Instrument Line Shape (ILS).

Carbon monoxide distribution from the ACE-FTS solar occultation measurements

This paper presents a comprehensive analysis of the CO observations acquired during the first eight months (January to September 2004) of the ACE mission. We show that the ACE high-resolution Fourier transform spectrometer (ACE-FTS), which operates in the solar occultation geometry and covers a wide spectral interval in the infrared, provides useful measurements in both the CO 1-0 and 2-0 vibrational bands. Vertically-resolved CO concentration profiles are retrieved, extending from the mid-troposphere to the thermosphere (from about 5 to 110 km). We have analyzed the latitudinal variability of the measurements, from which various physical and chemical atmospheric processes are highlighted for further study.

Global Chemistry Simulations in the AMMA Multimodel Intercomparison Project

The authors present results obtained during the chemistry-transport modeling (CTM) component of the African Monsoon Multi-disciplinary Analysis Multimodel Intercomparison Project (AMMA-MIP) using the recently developed L3JRCv2 emission dataset for Af-rica, where emphasis is placed on the summer of 2006. With the use of passive tracers, the authors show that the application of different parameterizations to describe advection, vertical diffusion, and convective mixing in a suite of state-of-the-art global CTMs results in significantly different transport mechanisms westward of the African continent. Moreover, the authors identify that the atmospheric composition over the southern Atlantic is governed by air masses originating from southern Africa for this period, resulting in maximal concentrations around 5°S. Comparisons with ozonesonde measurements at Cotonou (6.2°N, 2.2°E) indicate that the models generally overpredict surface ozone and underpredict ozone in the upper troposphere. Moreover, using recent aircraft measurements, the authors show that the high ozone concentrations that occur around 700 hPa around 5°N are not captured by any of the models, indicating shortcomings in the description of transport, the magnitude and/or location of emissions, or the in situ chemical ozone production by the various chemical mechanisms employed.

Ground-based solar absorption FTIR spectroscopy at the Reunion Island

This paper gives preliminary results of FTS atmospheric measurements at the Reunion Island. A special emphasis is given to the retrievals of CH4, CO, O3, N2O, HCl, HF and HNO3