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REMO-HAM is a new regional aerosol-climate model. It is based on the REMO regional climate model and includes most of the major aerosol processes. The structure for aerosol is similar to the global aerosol-climate model ECHAM5-HAM, for example the aerosol module HAM is coupled with a two-moment stratiform cloud scheme. On the other hand, REMO-HAM does not include an online coupled aerosol-radiation nor a secondary organic aerosol module. In this work, we evaluate the model and compare the results against ECHAM5-HAM and measurements. Four different measurement sites were chosen for the comparison of total number concentrations, size distributions and gas phase sulfur dioxide concentrations: Hyytiälä in Finland, Melpitz in Germany, Mace Head in Ireland and Jungfraujoch in Switzerland. REMO-HAM is run with two different resolutions: 50 × 50 km2 and 10 × 10 km2. Based on our simulations, REMO-HAM is in reasonable agreement with the measured values. The differences in the total number concentrations between REMO-HAM and ECHAM5-HAM can be mainly explained by the difference in the nucleation mode. Since we did not use activation nor kinetic nucleation for the boundary layer, the total number concentrations are somewhat underestimated. From the meteorological point of view, REMO-HAM represents the precipitation fields and 2 m temperature profile very well compared to measurement. Overall, we show that REMO-HAM is a functional aerosol-climate model, which will be used in further studies.

While Antarctica is often described as a pristine environment, there is an increasing awareness of the potential threats from local pollution sources including tourist ships and emissions associated with scientific activities. However, to date there has been no systematic attempt to model the impacts of such pollutants at the continental scale. Indeed, until very recently there was not even a sulphur emission budget available for Antarctica. Here we present the first comprehensive study of atmospheric pollution in Antarctica using a limited area chemistry climate model, and a monthly emissions inventory for sulphur from maintenance of research stations, ground and air traffic, shipping and the active Erebus volcano. We find that ship emissions, both sulphurous and black carbon, dominate anthropogenic pollution near the ground. Their prevalence is likely to rise dramatically if recent trends in tourism continue.

A glacier parameterization scheme has been developed and implemented into the regional climate model REMO. The new scheme interactively simulates the mass balance as well as changes of the areal extent of glaciers on a subgrid scale. The temporal evolution and the general magnitude of the simulated glacier mass balance in the European Alps are in good accordance with observations for the period 1958–1980, but the strong mass loss towards the end of the twentieth century is systematically underestimated. The simulated decrease of glacier area in the Alps between 1958 and 2003 ranges from -17.1 to -23.6%. The results indicate that observed glacier mass balances can be approximately reproduced within a regional climate model based on simplified concepts of glacier-climate interaction. However, realistic results can only be achieved by explicitly accounting for the subgrid variability of atmospheric parameters within a climate model grid box.

The Arctic plays a major role in the global circulation, and its water and energy budget is not as well explored as that in other regions of the world. The aim of this study is to calculate the climatological mean water and energy fluxes depending on the season and on the North Atlantic Oscillation (NAO) through the lower, lateral, and upper boundaries of the Arctic atmosphere north of 70°N. The relevant fluxes are derived from results of the regional climate model (REMO 5.1), which is applied to the Arctic region for the time period 1979–2000. Model forcing data are a combination of 15-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-15) data and analysis data. The annual and seasonal total water and energy fluxes derived from REMO 5.1 results are very similar to the fluxes calculated from observational and reanalysis data, although there are some differences in the components. The agreement between simulated and observed total fluxes shows that these fluxes are reliable. Even if differences between high and low NAO situations occur in our simulation consistent with previous studies, these differences are mostly smaller than the large uncertainties due to a small sample size of the NAO high and low composites.

The influence of two simple descriptions for the sea ice distribution on boundary layer values is investigated by comparing model results from the regional climate model REMO with measured data in the Fram Strait in April 1999. One method for determining the sea ice distribution in REMO is to diagnose the sea ice cover from the prescribed surface temperature and allow each grid cell to be either completely free of ice or completely covered by ice (REMO-original). The other one is to employ a partial sea ice concentration in each REMO grid cell with the input data derived from satellite data (REMO-partial). Surface fluxes are average values of the ice and water partial fluxes. There is a clearly better agreement between measured and simulated surface and boundary layer temperatures and humidities when using REMO-partial compared to REMO-original. The closed ice cover in REMO-original leads to downward sensible heat fluxes over ice, whereas the ice cover with leads and polynyas in REMO-partial leads to smaller downward or even upward sensible heat fluxes. The introduction of the partial sea ice concentration smoothes unrealistically sharp gradients between ice-covered and ice-free regions. which can influence cloud cover and precipitation. An additional result of the study is that the simulation of the albedo could be improved in allowing a larger range of sea ice albedos and introducing a water albedo dependent on sun zenith angle.

The REMO regional climate model was applied for a simulation experiment on the European climate of the Younger C Dryas, a distinct cooling event at the end of the last glacial. This regional simulation-with a 0.5 X 0.5 degrees latitude-longitude resolution-was 'nested' in an experiment carried out with the ECHAM4/T42 atmospheric general circulation model. The objective is to evaluate the advantages of a regional climate model (compared to a global model) for palaeoclimate research. Therefore, we compared our regional and global Younger Dryas experiments with climate reconstructions based on palaeodata. The comparison reveals that both models simulate a similar Younger Dryas climate, In some instances, REMO simulates a YD climate that is in better agreement with palaeodata than ECHAM4, most notably for precipitation and winter temperatures. Moreover, the higher spatial resolution of REMO, giving a more realistic presentation of the topography, provides regional climatic information, such as precipitation and temperature gradients, that is valuable for palaeoclimate data studies. Consequently, our results illustrate the perspective of regional climate models for palaeoclimate studies. (C) 2001 Elsevier Science B.V. All rights reserved.