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, H 2 O, O 3 , CH 4 , N 2 O, HNO 3 , and NO 2 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, itCorrespondence to: H. Fischer (herbert.fischer@imk.fzk.de) 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 NO y 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 NO x 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.

[1] The global distribution and budget of atmospheric molecular hydrogen (H 2 ) is simulated with a global Chemistry-Transport Model (CTM). Surface emissions include technological sources (industry, transportation and other fossil fuel combustion processes), biomass burning, nitrogen fixation in soils, and oceanic activity and totals 39 Tg/yr. The photochemical production (31 Tg/yr) from formaldehyde photolysis accounts for about 45% of the total source of H 2 . Soil uptake (55 Tg/yr) represents a major loss process for H 2 and contributes for 80% to the total destruction. H 2 oxidation by OH in the troposphere contributes the remainder. The global burden of H 2 in the atmosphere is 136 Tg. Its overall lifetime in the atmosphere is 1.9 years. H 2 is rather well-mixed in the free troposphere. However, its distribution shows a significant seasonal variation in the lower troposphere where soil uptake dominates. This loss process shows a strong temporal variability and is maximum over the northern hemisphere landmass during summer. Strong vertical gradients result from this surface uptake. In these regions, H 2 varies by more than 30% between the maximum mixing ratio in winter and the summer minimum. Our results stress the important role played by the tropics in the budget of H 2 . In these regions a strong seasonal cycle is also predicted due to the annual variation in biomass burning emissions, soil uptake, and rapid transport by convection of H 2 depleted air masses from the boundary layer to the upper troposphere. A comparison with the observed H 2 distribution allows to test some of the model predictions. Good agreement is found for the global burden and the annually averaged latitudinal gradient in the southern hemisphere and the tropics. A detailed comparison of the seasonal cycles of H 2 in surface air indicates that the use of the net primary productivity to prescribe the seasonal and geographical pattern of soil uptake in the model leads to an underestimate of the deposition velocity during winter and spring over the continents in the northern hemisphere.

No abstract

Abstract.OH and the major parameters determining its concentration were measured during a field campaign in August 1394 at Mankmoos, a rural, relatively unpolluted site in northeastern Germany. The measured OH concentrations were previously shown to depend mainly on the intensity of solar UV and on the mixing ratio of NO2. In this paper we develop a simple parameterization of the dependence on solar UV and on NO2. The photolysis of O3 to O•D, of NO2 to NO, and of HCHO to HCO and H, all contribute significantly to the total dependence of OH on solar UV. We demonstrate that the photolysis frequency of O3, Jots, is a suitable measure for that dependence which is slightly less than linear. The highly nonlinear dependence of OH on NOx is approximated by a Pad• function. The parameterization provides a tool for a future quantitative intercomparison of the measured and modeled dependences of OH on UV and NO2. It also allows the removal of the variation in the measured OH induced by the dependences on the variables, UV and NO2, and thus enables a search for dependences on other, less influential parameters.

A B S T R A C TThe literature on the distribution, budget and isotope content of molecular hydrogen (H 2 ) in the troposphere is critically reviewed. The global distribution of H 2 is reasonably well established and is relatively uniform. The surface measurements exhibit a weak latitudinal gradient with 3% higher concentrations in the Southern Hemisphere and seasonal variations that maximize in arctic latitudes and the interior of continents with peak-to-peak amplitudes up to 10%. There is no evidence for a continuous long-term trend, but older data suggest a reversal of the interhemispheric gradient in the late 1970s, and an increase in the deuterium content of H 2 in the Northern Hemisphere from 80 standard mean ocean water (SMOW) in the 1970s to 130 today. The current budget analyses can be divided in two classes: bottom up, in which the source and sink terms are estimated separately based on emission factors and turnovers of precursors and on global integration of regional loss rates, respectively. That category includes the analyses by 3-D models and furnishes tropospheric turnovers around 75 Tg H 2 yr −1 . The other approach, referred to as top down, relies on inverse modelling or analysis of the deuterium budget of tropospheric H 2 . These provide a global turnover of about 105 Tg H 2 yr −1 . The difference is due to a much larger sink strength by soil uptake and a much larger H 2 production from the photochemical oxidation of volatile organic compounds (VOC) in the case of the top down approaches. The balance of evidence seems to favour the lower estimates-mainly due to the constraint placed by the global CO budget on the H 2 production from VOC. An update of the major source and sink terms yields: fossil fuel use 11 ± 4 Tg H 2 yr −1 ; biomass burning (including bio-fuel) 15 ± 6 Tg H 2 yr −1 ; nitrogen fixation (ocean) 6 ± 3 Tg H 2 yr −1 ; nitrogen fixation (land) 3 ± 2 Tg H 2 yr −1 ; photochemical production from CH 4 23 ± 8 Tg H 2 yr −1 and photochemical production from other VOC 18 ± 7 Tg H 2 yr −1 . The loss through reaction of H 2 with OH is 19 ± 5 Tg H 2 yr −1 , and soil uptake 60Tg H 2 yr −1 . All these rates are well within the ranges of the corresponding bottom up estimates in the literature. The total loss of 79 Tg H 2 yr −1 combined with a tropospheric burden of 155 Tg H 2 yields a tropospheric H 2 lifetime of 2 yr. Besides these major sources of H 2 , there are a number of minor ones with source strengths <1 Tg H 2 yr −1 . Rough estimates for these are also given.