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Abstract:

The HIRDLS instrument is a limb viewing infra-red radiometer on the NASA Aura spacecraft in a sun synchronous low earth orbit and obtains measurements of the composition of the atmosphere covering the whole Earth each day. The MIPAS instrument is a limb viewing infra-red interferometer on board the European Envisat satellite in a very similar orbit to Aura except that the local solar time is different. The complement of geophysical data products of both instruments is very similar, and because of similar observation strategies their two data sets can be usefully compared. The comparison provides the means to 91̽»¨ validation in order to obtain statistics such as systematic differences and variance. This is performed over the full latitude range of HIRDLS and height range of MIPAS and thereby helps to identify sources of errors. The identification of known atmospheric features is a useful diagnostic, and includes such things as regions of upwelling of tracer gases, or the propagation of coherent structures as with mid-latitude waves and we can test whether these structures are consistently represented in both data sets. HIRDLS version 2.04.19 (v004) temperature, ozone and nitric acid show very low systematic 'errors' compared to MIPAS over most of the spatial range. Currently pre-released water vapour, nitrous oxide and F-11 are reasonably similar, CH4 somewhat more restricted, and nitrogen dioxide, N2O5, chlorine nitrate and F-12 as yet susceptible to complications from the obstructed telescope. Further details are discussed in the paper.

Abstract:

MIPAS, the Michelson Interferometer for Passive Atmospheric Sounding, is a mid-infrared emission spectrometer which is part of the core payload of ENVISAT. It is a limb sounder, i.e. it scans across the horizon detecting atmospheric spectral radiances which are inverted to vertical temperature, trace species and cloud distributions. These data can be used for scientific investigations in various research fields including dynamics and chemistry in the altitude region between upper troposphere and lower thermosphere. The instrument is a well calibrated and characterized Fourier transform spectrometer which is able to detect many trace constituents simultaneously. The different concepts of retrieval methods are described including multi-target and two-dimensional retrievals. Operationally generated data sets consist of temperature, H2O, O3, CH4, N2O, HNO3, and NO2 profiles. Measurement errors are investigated in detail and random and systematic errors are specified. The results are validated by independent instrumentation which has been operated at ground stations or aboard balloon gondolas and aircraft. Intercomparisons of MIPAS measurements with other satellite data have been carried out, too. As a result, it has been proven that the MIPAS data are of good quality. MIPAS can be operated in different measurement modes in order to optimize the scientific output. Due to the wealth of information in the MIPAS spectra, many scientific results have already been published. They include intercomparisons of temperature distributions with ECMWF data, the derivation of the whole NOy family, the study of atmospheric processes during the Antarctic vortex split in September∼2002, the determination of properties of Polar Stratospheric Clouds, the downward transport of NOx in the middle atmosphere, the stratosphere- troposphere exchange, the influence of solar variability on the middle atmosphere, and the observation of Non-LTE effects in the mesosphere.

Abstract:

Clouds are a source of major uncertainty in climate models - it is thus important to accurately model clouds in order to determine their properties. In this work, three cloud parameters (cloud top height, cloud top temperature and cloud extinction coefficient) are used to model the radiance measured in the MIPAS field-of-view as they represent the most obvious physical, thermodynamic and optical properties, respectively, of a cloud. Finally, this model is implemented in an optimal estimations-type retrieval of cloud top height, temperature and extinction co-efficient from real MIPAS spectra.

Abstract:

The main advantage in combining limb and nadir geometries is that it allows the stratospheric and tropospheric ozone concentrations to be separated which makes it possible to improve the tropospheric ozone retrieval. This paper presents the retrieval method which will be used to combine TES nadir measurements with MIPAS limb measurements and shows some preliminary results. The Tropospheric Emission Spectrometer (TES) is a high-spectral-resolution infrared imaging Fourier transform spectrometer operated by NASA's Jet Propulsion Laboratory(JPL). It has a spectral range from 3.2/μm to 15.4/μm and at present is mostly operating in the nadir mode. TES routinely measures temperature and concentrations of O3,H2O, CH4, CO, HNO3, and N2O. A local optimal estimation retrieval code (the MIPAS Orbital Retrieval using Sequential Estimation (MORSE)) was used to retrieve Volume Mixing Ratios (VMR's) from the low resolution ESA level IB MIPAS data and level IB TES data. A joint retrieval was achieved by using the MIPAS retrieved VMR profiles as the a priori for the TES retrieval. A similar method could be used in the future to combine MIPAS and IASI.

Abstract:

Ozone isotope data for 50O3 and 49O 3 are retrieved from MIPAS limb emission spectra. Enrichments for 50O3 range 7 to 12% in the middle stratosphere. For 49O3 most enrichments are between 7 and 10%. In stratosphere (25-40 km) these measurements are in agreement with previous measurements (e.g. FIRS) and with expectations based on laboratory measurements. Above 40 km and below 25 km, the enrichments of both 50O3 and 49O3 get larger, from 30 to 50%. MIPAS enrichments show latitude and altitude structure.