[1] In this paper we investigate daily variations in middle atmospheric water vapor and ozone based on data from two ground-based microwave radiometers located in the Alpine region of Europe. Temperature data are obtained from a lidar located near the two stations and from the SABER experiment on the TIMED satellite. This unique set of observations is complemented by three different three-dimensional (3-D) chemistry-climate models (Monitoring of Stratospheric Depletion of the Ozone Layer (MSDOL), Laboratoire de Météorologie Dynamique Reactive Processes Ruling the Ozone Budget in the Stratosphere (LMDz-REPROBUS), and Solar Climate Ozone Links (SOCOL)) and the 2-D atmospheric global-scale wave model (GSWM). The first part of the paper is focused on the first Climate and Weather of the Sun-Earth System (CAWSES) tidal campaign that consisted of a period of intensive measurements during September 2005. Variations in stratospheric water vapor are found to be in the order of 1% depending on altitude. Meridional advection of tidal nature is likely to be the dominant driving factor throughout the whole stratosphere, while vertical advection becomes more important in the mesosphere. Observed ozone variations in the upper stratosphere and lower mesosphere show amplitudes of several percent in accordance with photochemical models. Variations in lower stratospheric ozone are not solely governed by photochemistry but also by dynamics, with the temperature dependence of the photochemistry becoming more important. The second part presents an investigation of the seasonal dependence of daily variations. Models tend to underestimate the H 2 O diurnal amplitudes, especially during summer in the upper stratosphere. Good agreement between models and observations is found for ozone in the upper stratosphere, which reflects the fact that the O 3 daily variations are driven by the photochemistry that is well modeled.

We have compared composition changes of NO, NO₂, H₂O₂, O₃, N₂O, HNO₃, N₂O₅, HNO₄, ClO, HOCl, and ClONO₂ as observed by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat in the aftermath of the "Halloween" solar proton event (SPE) in October/November 2003 at 25–0.01 hPa in the Northern Hemisphere (40–90&deg; N) and simulations performed by the following atmospheric models: the Bremen 2d Model (B2dM) and Bremen 3d Chemical Transport Model (B3dCTM), the Central Aerological Observatory (CAO) model, FinROSE, the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA), the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model, the modeling tool for SOlar Climate Ozone Links studies (SOCOL and SOCOLi), and the Whole Atmosphere Community Climate Model (WACCM4). The large number of participating models allowed for an evaluation of the overall ability of atmospheric models to reproduce observed atmospheric perturbations generated by SPEs, particularly with respect to NO_y and ozone changes. We have further assessed the meteorological conditions and their implications on the chemical response to the SPE in both the models and observations by comparing temperature and tracer (CH₄ and CO) fields. <br><br> Simulated SPE-induced ozone losses agree on average within 5% with the observations. Simulated oy enhancements around 1 hPa, however, are typically 30% higher than indicated by the observations which can be partly attributed to an overestimation of simulated electron-induced ionization. The analysis of the observed and modeled NO_y partitioning in the aftermath of the SPE has demonstrated the need to implement additional ion chemistry (HNO₃ formation via ion-ion recombination and water cluster ions) into the chemical schemes. An overestimation of observed H₂O enhancements by all models hints at an underestimation of the OH/HO₂ ratio in the upper polar stratosphere during the SPE. The analysis of chlorine species perturbations has shown that the encountered differences between models and observations, particularly the underestimation of observed ClONO₂ enhancements, are related to a smaller availability of ClO in the polar night region already before the SPE. In general, the intercomparison has demonstrated that differences in the meteorology and/or initial state of the atmosphere in the simulations causes a relevant variability of the model results, even on a short timescale of only a few days

Abstract. The mesospheric hydroxyl radical (OH) is mainly produced by the water vapor (H 2 O) photolysis and could be considered as a proxy for the influence of the solar irradiance variability on the mesosphere. We analyze the tropical mean response of the mesospheric OH and H 2 O data as observed by the Aura Microwave Limb Sounder (MLS) to 27-day solar variability. The analysis is performed for two time periods corresponding to the different phases of the 11-yr cycle: from December 2004 to December 2005 (the period of "high activity" with a pronounced 27-day solar cycle) and from August 2008 to August 2009 ("solar minimum" period with a vague 27-day solar cycle). We demonstrate, for the first time, that in the mesosphere the daily time series of OH concentrations correlate well with the solar irradiance (correlation coefficients up to 0.79) at zero time-lag. At the same time H 2 O anticorrelates (correlation coefficients up to −0.74) with the solar irradiance at non-zero time-lag. We found that the response of OH and H 2 O to the 27-day variability of the solar irradiance is strong for the period of the high solar activity and negligible for the solar minimum conditions. It allows us to suggest that the 27-day cycle in the solar irradiance and in OH and H 2 O are physically connected.

Ozone depletion is caused by the anthropogenic increase of halogen-containing species in the atmosphere, which results in the enhancement of the concentration of reactive chlorine and bromine in the stratosphere. To reduce the influence of anthropogenic ozone-depleting substances (ODS), the Montreal Protocol was agreed by Governments in 1987, with several Amendments and Adjustments adopted later. In order to assess the benefits of the Montreal Protocol and its Amendments and Adjustments (MPA) on ozone and UV radiation, two different runs of the chemistry-climate model (CCM) SOCOL have been carried out. The first run was driven by the emission of ozone depleting substances (ODS) prescribed according to the restrictions of the MPA. For the second run we allow the ODS to grow by 3% annually. We find that the MPA would have saved up to 80% of the global annual total ozone by the end of the 21st century. Our calculations also show substantial changes of the stratospheric circulation pattern as well as in surface temperature and precipitations that could occur in the world without MPA implementations. To illustrate the changes in UV radiation at the surface and to emphasise certain features, which can only be seen for some particular regions if the influence of the cloud cover changes is accounted for, we calculate geographical distribution of the erythemally weighted irradiance (E_ery). For the no Montreal Protocol simulation E_ery increases by factor of 4 to 16 between the 1970s and 2100. For the scenario including the Montreal Protocol it is found that UV radiation starts to decrease in 2000, with continuous decline of 5% to 10% at middle latitudes in the both Northern and Southern Hemispheres

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