Abstract. For the purpose of qualifying and quantifying the climate impact of cities and urban surfaces in general on climate of central Europe, the surface parameterization in regional climate model RegCM4 has been extended with the Single-layer Urban Canopy Model (SLUCM). A set of experiments was performed over the period of 2005-2009 for central Europe, either without considering urban surfaces or with the SLUCM treatment. Results show a statistically significant impact of urbanized surfaces on temperature (up to 1.5 K increase in summer) as well as on the boundary layer height (increases up to 50 m). Urbanization further influences surface wind with a winter decrease up to −0.6 m s −1 , though both increases and decreases were detected in summer depending on the location relative to the cities and daytime (changes up to 0.3 m s −1 ). Urban surfaces significantly reduce the humidity over the surface. This impacts the simulated summer precipitation rate, showing a decrease over cities of up to −2 mm day −1 . Significant temperature increases are simulated over higher altitudes as well, not only within the urban canopy layer. With the urban parameterization, the climate model better describes the diurnal temperature variation, reducing the cold afternoon and evening bias of RegCM4.Sensitivity experiments were carried out to quantify the response of the meteorological conditions to changes in the parameters specific to the urban environment, such as street width, building height, albedo of the roofs and anthropogenic heat release. The results proved to be rather robust and the choice of the key SLUCM parameters impacts them only slightly (mainly temperature, boundary layer height and wind velocity).Statistically significant impacts are modelled not only over large urbanized areas, but the influence of the cities is also evident over rural areas without major urban surfaces. It is shown that this is the result of the combined effect of the distant influence of the cities and the influence of the minor local urban surface coverage.

Abstract. In general, regional and global chemistry transport models apply instantaneous mixing of emissions into the model's finest resolved scale. In case of a concentrated source, this could result in erroneous calculation of the evolution of both primary and secondary chemical species. Several studies discussed this issue in connection with emissions from ships and aircraft. In this study, we present an approach to deal with the non-linear effects during dispersion of NO x emissions from ships. It represents an adaptation of the original approach developed for aircraft NO x emissions, which uses an exhaust tracer to trace the amount of the emitted species in the plume and applies an effective reaction rate for the ozone production/destruction during the plume's dilution into the background air. In accordance with previous studies examining the impact of international shipping on the composition of the troposphere, we found that the contribution of ship induced surface NO x to the total reaches 90% over remote ocean and makes 10-30% near coastal regions. Due to ship emissions, surface ozone increases by up to 4-6 ppbv making 10% contribution to the surface ozone budget. When applying the ship plume parameterization, we show that the large scale NO x decreases and the ship NO x contribution is reduced by up to 20-25%. A similar decrease was found in the case of O 3 . The plume parameterization suppressed the ship induced ozone production by 15-30% over large areas of the studied region. To evaluate the preCorrespondence to: P. Huszar (huszarpet@gmail.com) sented parameterization, nitrogen monoxide measurements over the English Channel were compared with modeled values and it was found that after activating the parameterization the model accuracy increases.

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This study presents an interactive coupling system of the regional climate model RegCM3 and the chemistry transport model CAMx, called RegCMCAMx. This system provides an advancement from offline coupling methods already in use. In RegCMCAMx, the radiative effects of tropospheric ozone, sulfates and black and organic carbon were considered. A series of annual sensitivity simulations were carried out for the year 2005 over a European domain, where ozone and/or aerosols were interactively coupled (taking their radiative feedbacks into account). The simulated concentrations of ozone, nitrogen dioxide, sulfur dioxide, sulfate and carbonaceous aerosol were validated against surface measurements. The coupling was evaluated by simulating 2 m temperature as well. The model satisfactorily reproduced near-surface ozone, especially in summer, and made reasonable predictions for monthly sulfate aerosol concentrations. Deficiencies were identified in simulating nitrogen (underprediction), sulfur oxides (overprediction) and carbonaceous aerosols (underprediction). The performance of the coupling system compared to non-coupled data was analyzed, and significant improvement of the model was found in terms of reproducing 2 m temperature, mainly for interactively coupled ozone. The short-term climate response of interactively coupled chemistry/aerosol was analyzed for the first time by this coupling model as well. The seasonally averaged temperature perturbation caused by coupled ozone/aerosols ranged from −1.5 to +1.5°C, not only near the surface but also at higher altitudes. Despite expectations, the surface radiative forcing due to aerosols did not correlate with the induced temperature changes, reflecting the complexity of the processes when ozone and/or aerosols perturb the overall dynamics of the atmosphere. The limitations of the newly established coupling system and the potential for future development are discussed.