Hendrik Feldmann

The use of nested models for air pollution studies: an application of the EURAD model to a SANA episode

Abstract A multiple-nesting version of the European Acid Deposition Model (EURAD) has been developed in order to increase the horizontal resolution in a region of enhanced pollution, namely the former German Democratic Republic. This new technique allows the ability to simulate large-scale features together with the development of smaller-scale structures in the nested regions. This multiple-nesting approach was applied to a case that occurred in October 1990, the so-called SANA 1 episode. SANA is a German acronym that stands for “scientific program for the assessment of the air pollution situation in the former German Democratic Republic.” The SANA program was established to observe the rapid change in composition of air pollutants and their concentration levels over the eastern part of Germany due to political and economical changes. Thus, within the SANA program there is a unique chance to observe and control the effect of air quality strategies. Two nested areas are embedded in a coarse domain that co...

Evaluation studies with a regional chemical transport model (EURAD) using air quality data from the EMEP monitoring network

Abstract The EURAD model has been applied to simulate the transport and chemical transformations of atmospheric constituents over central Europe for a 3 week late winter episode in February/March 1982. The TADAP model (the European version of ADOM) carried out simulations for the same episode with the same emission data set but with different meteorological input. The episode is characterized by two typical European meteorological conditions: a relatively quiet blocking situation at the beginning of the episode is followed by rather disturbed conditions with frontal systems passing through central European. The evolution of the pollutant fields is markedly different during these two conditions. Evaluation studies with the focus on the sulfur species were performed using air quality data from the EMEP monitoring network for the comparison of model predictions with observations. The first simulation with predicted meteorology and the PHOXA emission data set revealed an underprediction of airborne sulfate and wet deposition, while SO 2 was overpredicted. A simulation with meteorological data created by a so-called nudging technique corrected the transport of SO 2 to remote regions and drastically improved the predictions of rainfall and subsequently the amount of wet deposition. However, the ambient sulfate aerosol concentrations were still underpredicted. As the same bias in sulfate was also observed for TADAP simulations of the same episode a hypothesis for the underprediction is a very low primary sulfate emission inherent in the emission database. By artificially increasing the primary sulfate emission to an obviously too high value, the underprediction of sulfate was changed into a strong overprediction for the major source regions and into a reasonable range as observed for the remote regions. An analysis of the precipitation amounts, the aqueous concentrations and the resulting wet deposition showed that during this episode the aqueous were precipitation limited.

Evaluation of the precipitation for South-western Germany from high resolution simulations with regional climate models

Precipitation data from long-term high-resolution simulations with two regional climate models (CLM and REMO) are evaluated using a climatology based on observations for south-western Germany. Both models are driven by a present day climate forcing scenario from the global climate model ECHAM5. The climatological evaluation shows a strong seasonal dependence of the model deficiencies. In spring and summer there are relatively small differences between simulation results and observations. But during winter both the regional models and ECHAM5 strongly overestimate the precipitation. The frequency distributions of the model results agree well with observed data. An overestimation of the precipitation at the upwind sides of mountainous areas occurs in the regional simulations. We found that the coupling of the regional models to the driving model is stronger in winter than in summer. Therefore, in winter the large scale model have a larger impact on the performance of the regional simulations. During summer the benefit of regional climate simulations is higher.

Long-term simulations of particulate matter in Europe on different scales using sequential nesting of a regional model

A regional model system for the simulation of air quality in Europe (EURAD) has been employed for long-term calculations of atmospheric pollutants on different scales. The model allows sequential nesting. Starting with a domain covering most of Europe, the nesting procedure was used to scale down the simulations to a highly populated and industrialized area, namely NorthRhine-Westphalia (NRW). The analysis of results is focusing on the simulation of particulate matter (PM10) for the year 1997. This parameter is of special interest in the framework of air pollution control as demanded by the European Union. The model takes account of various components of the atmospheric aerosol, including secondary organic aerosols (SOA). Their role in the budget of particulate matter is briefly shown. The model data are compared with measurements of the monitoring network of NRW. Hit rates for a given range of accuracy are discussed for PM10 and NO2. It is found that a large part of deviating results may be ascribed to shortcomings in the applied aerosol emission inventories, in particular, and that it is worthwhile to improve them for the application to future air quality assessments based on numerical simulations.

South foehn and ozone in the Eastern Alps – case study and climatological aspects

Abstract The ozone situation in the Eastern Alps was investigated during the south foehn period from 4–6 May 1997. The event was studied in detail using surface measurements, soundings and aircraft measurements of meteorological and chemical parameters. A numerical simulation with a prognostic meteorological model (MM5) and a chemistry-transport model with 6 km resolution provided additional insight. The case study was supplemented by a climatological evaluation of a three-year data set. The foehn period was preceeded by an ozone episode in the Po Basin south of the Alps. Advection of residual-layer air masses from that area caused a maximum of the ozone concentration in the beginning. Later on, the ozone concentration in the foehn area was determined by a mixture of regional-scale advection from the lower free troposphere and boundary-layer air from the south. The contribution of boundary-layer air was especially strong in the lee of the deep gap formed by the Brenner Pass and visible in many parameters. The climatological evaluation showed that during south foehn, ozone concentrations are elevated in the foehn area, especially in the valleys and during nighttime where the usual nocturnal minimum is suppressed.

High-resolution sensitivity studies with the regional climate model COSMO-CLM

This paper presents sensitivity studies with the regional climate model COSMO-CLM for southwest Germany and the period from 1991 to 2000. The influence of horizontal resolution (7 km and 14 km) and driving data (ERA-40 and NCEP reanalysis data) on simulation results are assessed and a suitable simulation setup for high-resolution simulations is derived by using varying domain sizes, soil moisture initialization, physical parameterizations and numerical schemes. The use of ERA-40 reanalyses as driving data yields better overall results for temperature and precipitation than the use of NCEP reanalysis data. Increase in the horizontal resolution leads to better simulation results compared to observations. The choice of driving data has a larger impact on simulation results than changing resolutions, physical parameterizations, numerical schemes or initial soil water contents for simulations of this area.

High-Resolution Climate Change Impact Analysis on Medium-Sized River Catchments in Germany: An Ensemble Assessment

AbstractThe impact of climate change on three small- to medium-sized river catchments (Ammer, Mulde, and Ruhr) in Germany is investigated for the near future (2021–50) following the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario. A 10-member ensemble of hydrological model (HM) simulations, based on two high-resolution regional climate models (RCMs) driven by two global climate models (GCMs), with three realizations of ECHAM5 (E5) and one realization of the Canadian Centre for Climate Modelling and Analysis version 3 (CCCma3; C3) is established. All GCM simulations are downscaled by the RCM Community Land Model (CLM), and one realization of E5 is downscaled also with the RCM Weather Research and Forecasting Model (WRF). This concerted 7-km, high-resolution RCM ensemble provides a sound basis for runoff simulations of small catchments and is currently unique for Germany. The hydrology for each catchment is simulated in an overlapping scheme, with t...

Determination of precipitation return values in complex terrain and their evaluation.

To determine return values at various return periods for extreme daily precipitation events over complex orography, an appropriate threshold value and distribution function are required. The return values are calculated using the peak-over-threshold approach in which only a reduced sample of precipitation events exceeding a predefined threshold is analyzed. To fit the distribution function to the sample, the L-moment method is used. It is found that the deviation between the fitted return values and the plotting positions of the ranked precipitation events is smaller for the kappa distribution than for the generalized Pareto distribution. As a second focus, the ability of regional climate models to realistically simulate extreme daily precipitation events is assessed. For this purpose the return values are derived using precipitation events exceeding the 90th percentile of the precipitation time series and a fit of a kappa distribution. The results of climate simulations with two different regional climate models are analyzed for the 30-yr period 1971–2000: the so-called consortium runs performed with the climate version of the Lokal Modell (referred to as the CLM-CR) at 18-km resolution and the Regional Model (REMO)–Umweltbundesamt (UBA) simulations at 10-km resolution. It was found that generally the return values are overestimated by both models. Averaged across the region the overestimation is higher for REMO–UBA compared to CLM-CR.

MiKlip - a National Research Project on Decadal Climate Prediction

AbstractMittelfristige Klimaprognose (MiKlip), an 8-yr German national research project on decadal climate prediction, is organized around a global prediction system comprising the Max Planck Institute Earth System Model (MPI-ESM) together with an initialization procedure and a model evaluation system. This paper summarizes the lessons learned from MiKlip so far; some are purely scientific, others concern strategies and structures of research that target future operational use.Three prediction system generations have been constructed, characterized by alternative initialization strategies; the later generations show a marked improvement in hindcast skill for surface temperature. Hindcast skill is also identified for multiyear-mean European summer surface temperatures, extratropical cyclone tracks, the quasi-biennial oscillation, and ocean carbon uptake, among others. Regionalization maintains or slightly enhances the skill in European surface temperature inherited from the global model and also displays h...

Evaluation Of A Regional Scale Model For The Alpine Region With Data From The VOTALP Project

One of the VOTALP key questions is dedicated to the influence of stratospheric intrusions on the ozone concentrations at the Alpine peak level. Measurements of ozone, beryllium-7 and other components are made at a number of mountain peak sites. In addition LIDAR measurements are used A tropopause folding event in May/June 1996 has been selected to study the relevant processes in more detail (Feldmann et a/., 1998). Model calculations are performed to estimate the fluxes of ozone into the Alps during the episode.