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With the launch of ENVISAT in 2001, the high-resolution mid-IR FTS MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) limb emission sounder will be brought into a close-to polar orbit at 800 km altitude. In the scientific data analyses vertical profiles of the temperature and of the volume mixing ratio (vmr) of some 20 species are retrieved. To accelerate the calculations, and hence to maximize the throughput, it is desirable to have initial guess profiles available which are as close as possible to the true profiles. To asses the retrived profiles, and for retrievals with the method of optimal estimation, a-priori knowledge together with related error estimates is furthermore needed. We present a system to generate suitable initial guess profiles, which consists of a data base and corresponding tools to support the scientific data processing. The data base contains individual vmr-profiles for various conditions, meteorological data for the temperature (ECMWF), and climatologies for temperature (MSISE90) and vmr (CIRA, URAP), and corresponding error estimates. [Copyright &y& Elsevier]

The MIPAS spectrometer onboard the Envisat platform observed infrared emission from the Earth's limb between 2002 and 2012. It recorded high-resolution spectra during day and night, from pole to pole and between 6 and 70 km altitude in the nominal measurement mode or up to 170 km in special measurement modes, producing daily more than 1000 vertical profiles of various trace gases. The operational Level-2 data are processed by ESA/DLR but there exist three other, independent research Level-2 processors that are hosted by ISAC-CNR/University of Bologna, Oxford University, and KIT IMK/IAA. All four Level-2 processors rely on the same Level-1b data provided by ESA but their retrieval schemes differ. As part of ESA's Ozone Climate Change Initiative project, an intercomparison of the four MIPAS processors took place, in which vertical ozone profiles retrieved by these four processors from MIPAS nominal mode measurements were compared for 2007 and 2008. We present the results of this comparison exercise, which consisted of five parts: an information content study of the vertical averaging kernels, an intercomparison of zonal seasonal means and spreads, a determination of biases through comparison to ozonesonde and lidar measurements, a comparison to other satellite records (bias estimation and precision assessment with respect to ACE-FTS and Aura-MLS data), and a geophysical validation of the provided error bars using MIPAS–MIPAS collocations. The four processors demonstrate similar performance. All processors use the same Level-1b data from ESA, apply global fits, and use microwindows instead of the full spectrum. The main differences in the processing schemes include the choice of microwindows, the regularization approach, the treatment of negative retrieved values, and the cloud detection threshold. The different regularization schemes lead to a different trade-off between noise and resolution, but without a clear average advantage for any particular data set. The vertical resolution is typically 3–5 km and the single profile precision is about 2–3%. In the middle and upper stratosphere, at 25–45 km, all four MIPAS processors clearly show a high bias of 2 to 5% relative to all reference instruments. The similarity of the structure and magnitude of the bias among the MIPAS data sets indicates that the bias is most likely linked to the use of microwindows of the MIPAS AB band. The satellite intercomparisons show furthermore that for the KIT dataset, the onset of the high bias starts at a somewhat higher altitude (only above 35 km) than for the other three datasets. This is likely due to the more restrictive use of the AB band by the KIT processor, which comes at the cost of a coarser vertical resolution near the ozone volume mixing ratio (vmr) peak. In the troposphere, the Level-2 algorithms that suppress negative ozone values in the iterative retrieval process produce a larger positive bias than the algorithm that does not follow such a strategy. Our main conclusion is that the four MIPAS processors are more similar to each other than to any other reference instrument. This indicates that the observed biases are very likely instrument-related. [ABSTRACT FROM AUTHOR]

Abstract: Daytime mesospheric limb emission spectra of ozone in the regime are analyzed with respect to vibrational excitation and relaxation processes. The data, which was obtained by the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) instrument on board ESA''s Environmental Satellite, is simulated by means of a non-local thermodynamic equilibrium (non-LTE) model utilizing -abundance, temperature, and pressure data from simultaneous retrievals in other spectral regions. The vibrational states of ozone depart from LTE due to the absorption of radiation from the lower atmosphere and due to the production of excited states in the recombination reaction. The energy flow into the ozone molecule as well as the collisional relaxation are highly uncertain. Model calculations that assume ozone formation at energies larger than underestimate the measured radiances by a factor of 2–3 in the 50–75km altitude regime, if the nominal relaxation scheme is assumed. Agreement between measured and modeled radiances is achieved, if the collisional rates for the transformation of hot band stretching to bending quanta are reduced by about a factor of three, or if the quasi-nascent distribution of ozone favors vibrational states in the region. [Copyright &y& Elsevier]

Abstract: With the successful launch of the European Space Agency’s Envisat satellite new possibilities for global night-time measurements of middle atmospheric ozone have emerged. The GOMOS and MIPAS instruments on board Envisat are able to measure ozone in both day and night conditions, which is especially important in the mesosphere where the diurnal variations of ozone are substantial. In this paper, we present a comparison of MIPAS and GOMOS night-time measurements. We show individual measurement profiles as well as statistical average profiles of stratospheric and mesospheric ozone from both instruments. Our conclusion is that the two instruments are generally in a good agreement throughout the middle atmosphere. [Copyright &y& Elsevier]

Abstract: In this work, we deal with the retrieval of O3 from the upper atmosphere data from 20 to 100 km using the high spectral resolution measurements of MIPAS in the regions of 14 and 10 μm. Non-LTE modelling of the O3 levels is included. Quality parameters of the retrievals and sensitivity tests for tuning the retrieval processor are presented. Day and nighttime O3 profiles and zonal O3 distribution for solstice conditions are shown to demonstrate the robustness and quality of the method. Finally a preliminary error assessment on the random and systematic errors, including non-LTE sources, is presented. [Copyright &y& Elsevier]

Abstract: Ozone volume mixing ratio (VMR) profiles are measured by the Michelson Interferometer for passive atmospheric sounding (MIPAS) on ENVISAT. The data sets produced by the science data processor at Institut für Meteorologie und Klimaforschung (IMK), Germany are compared with those obtained by halogen occultation experiment (HALOE) on UARS and by sub-millimetre radiometer (SMR) on ODIN. For the stratospheric measurements taken during September/October 2002, the three instruments show reasonable agreement, with global mean differences within 0.1–0.3ppmv. The typical zonal mean differences are of 0.4ppmv for HALOE and 0.6 ppmv for SMR (4–6%) in the ozone VMR peak region at 25–30km near the equator, though larger differences of 0.8–1 ppmv (8–10%) are also observed in a small latitude–altitude region in the tropic. A positive bias of about 0.2–0.4ppmv in the MIPAS data in the 35–40km region has also been found. Further studies are under way to explain these differences. [Copyright &y& Elsevier]

Abstract: Vertical profiles of O3 and NO2 abundances from the atmospheric instruments GOMOS (Global Ozone Monitoring by the Occultation of Stars), MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) and SCIAMACHY (Scanning Imaging Spectrometer for Atmospheric Chartography) all on-board the recently launched European Space Agency (ESA) Environmental Satellite (ENVISAT) are intercompared. These comparisons contribute to the validation of these data products by detecting systematic deviations, for example, wrong tangent height determinations, spectroscopic errors, and others. The cross comparison includes GOMOS data products retrieved by the GOMOS prototype processor from ACRI (Sophia Antipolis, France), the scientific SCIAMACHY data products from the Institute of Environmental Physics at University of Bremen (IUP) and the scientific MIPAS data products from the Institute for Meteorology and Climate Research in Karlsruhe (IMK) and Institute of Astrophysics in Andalusia (IAA). Coincident measurements were identified by limiting the time difference to 100min (duration of one orbit) and less than 500km between two observation points. When lower stratospheric ozone is strongly depleted during polar spring, a homogeneity condition was further imposed on the satellite measurements by requiring an upper limit on the potential vorticity difference at the 475K isentrope between both observations. Since geographically coincident NO2 measurements of the three instruments are performed during different times of the day and NO2 has a rather strong diurnal variability, matches of NO2 profiles were compared only where the solar zenith angle difference was below 5°. First results of the cross comparison show an agreement within 15% between 21 and 40km altitude for O3 profiles and an agreement within 20% between 27 and 40km altitude for NO2 profiles among the GOMOS, MIPAS and SCIAMACHY measurements. [Copyright &y& Elsevier]

On 1 March 2002, the European research satellite Envisat has been successfully launched. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board is a limb viewing mid-infrared high-resolution spectrometer. Among numerous atmospheric parameters, water vapor and temperature profiles will be retrieved from spectral data in an altitude range from 5 km up to the mesosphere. In this paper, we analyze MIPAS'' potential for spatially resolved water vapor measurements in the tropical tropopause region. A detailed pre-launch retrieval study, which includes error sources like random noise, smoothing error and error contributions due to interfering species, has shown that significant results can be obtained down to 10 km. The achievable accuracy is between 10% and 20% depending on the altitude range. By making use of a finer sampling grid in the tangent altitude domain a vertical resolution as good as 1.5–2 km can be reached. The impact of thin cirrus clouds on the infrared spectra measured by MIPAS has been simulated. [Copyright &y& Elsevier]