Abstract. This paper discusses the global analyses of stratospheric ozone (O 3 -VISAT). This corresponds to the entire period during which MIPAS was operating at its nominal resolution.Our analyses are evaluated against assimilated MIPAS data and independent HALOE (HALogen Occultation Experiment) and POAM-III (Polar Ozone and Aerosol Measurement) satellite data. A good agreement is generally found between the analyses and these datasets, in both cases within the estimated error bars of the observations. The benefit of data assimilation is also evaluated by comparing a BASCOE free model run with MIPAS observations. For O 3 , the gain from the assimilation is significant during ozone hole conditions, and in the lower stratosphere. Elsewhere, the assimilation does not provide significant improvement. For NO 2 , the gain from the assimilation is realized through most of the stratosphere. Using the BASCOE analyses, we estimate the differences between MIPAS data and independent data from HALOE and POAM-III, and find results close to those obtained by classical validation methods involving only direct measurement-to-measurement comparisons. Our results extend and reinforce previous MIPAS data validation Correspondence to: Q. Errera (quentin.errera@aeronomie.be) efforts by taking into account a much larger variety of atmospheric states and measurement conditions. This study discusses possible further developments of the BASCOE data assimilation system; these concern the horizontal resolution, a better filtering of NO 2 observations, and the photolysis calculation near the lid of the model. The ozone analyses are part of the PROMOTE project and are publicly available via the BASCOE website (www.bascoe. oma.be/promote).
Abstract.A new climatology of stratospheric BrO profiles based on a parameterization using dynamical and chemical indicators has been developed, with the aim to apply it to the retrieval of tropospheric BrO columns from space nadir measurements. The adopted parameterization is based on three years of output data from the 3-D chemistry transport model BASCOE. The impact of the atmospheric dynamics on the stratospheric BrO distribution is treated by means of Br y /ozone correlations built from 3-D-CTM model results, while photochemical effects are taken into account using stratospheric NO 2 columns as an indicator of the BrO/Br y ratio. The model simulations have been optimized for bromine chemistry and budget, and validated through comparisons using an extensive data set of ground-based, balloon-borne and satellite limb (SCIAMACHY) stratospheric BrO observations.
[1] In this paper the first time-dependent model of ion chemistry in the mesosphere/lower thermosphere (MLT) region acting within a global, time-dependent, two-dimensional neutral atmosphere model is described. Selected diurnal results are presented for undisturbed solar minimum conditions. The University of Bern Atmospheric Ion Model (UBAIM) is a time-dependent, pseudo-two-dimensional model of the ion chemistry in the Earth atmosphere. It covers latitudes from 85°S to 85°N and (log-pressure) altitudes from 20 to 120 km. On this grid a system of differential equations describing the ion chemistry is integrated numerically until a periodical solution, governed by the diurnal changes in the incident radiation, is reached; this solution constitutes a model for quiet or undisturbed conditions. The basic ion chemistry of the UBAIM contains 311 reactions for 71 charged species. Ionization sources are solar X-ray and EUV radiation, resonantly scattered Lyman a and b photons, and galactic cosmic rays. Densities of main and trace neutral atmospheric constituents are taken from a new version of the bidimensional NCAR model SOCRATES, which has been specifically optimized for mesospheric and lower thermospheric processes with upper boundary conditions set using the empirical MSIS thermosphere model. Direct solar flux inputs are computed by the SOLAR2000 model; scattered Lyman a and b fluxes are calculated using geocoronal hydrogen density profiles consistent with the adopted MSIS density distributions.
[1] Modelling the energy budget in the mesosphere and lower thermosphere requires a precise evaluation of CO 2 distribution in this region. This distribution is primarily determined by competition between vertical eddy diffusion and molecular diffusion. A simple algorithm is proposed to take into account both processes, at all altitudes. Using the SOCRATES bi-dimensional model of the middle atmosphere, we show that molecular diffusion has a direct impact on CO 2 vertical distribution down to approximately 80 km altitude, i.e. well into the mesosphere and below the turbopause altitude. A sensitivity study with regard to different aeronomical processes shows that molecular diffusion has the deepest influence in the mesospheric polar night region. Our model shows that molecular diffusion of CO 2 is responsible for a polar night mesopause 12 K warmer than if this process was neglected. Hence, dynamical models should take this process in account across the whole mesospheric altitude range.
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